Making Digital Camera Microscope Adapters

May, 2008.

This page describes the custom adapters I make to fit a variety of cameras, microscopes, and medical instruments, For most of these simpler mechanical adapters, I charge $85 to $175 (USD), depending on the complexity. Adapters incorporating optical elements are more complex and typically cost $400. Complete kits for medical and scientific instruments range from $400 to $2400. Old and new optical instruments are thereby fitted into the modern age of digital imaging. Besides the mechanical attachment, these adapters apply one of several optical principles to couple the camera to the microscope, including:

• Afocal (through the normal eyepiece to inexpensive small-format digital cameras)
• Focal (from a photoport to lensless digital SLR cameras)
• Focal (from a photoport to small-format digital cameras via a relay lens)
• Afocal (through a custom photo-eyepiece for large-lensed digital cameras)

As an example, you can inspect a 3D solid model for a typical adapter [Autodesk DWF file, 26 KB]. (This requires the free Autodesk DWF Viewer). The viewer allows you to rotate ("orbit"), pan and zoom the 3D model so you can see exactly what we are discussing. You can also view the mechanical drawing [PDF file, 30KB].

Here is another 3D model that shows a typical adapter and eyepiece nesting [Autodesk DWF file, 28 KB]. Rotate the model (using the "orbit" tool in the viewer) so you can see how the custom adapter closely fits the supplied microscope eyepiece.

And here is one more 3D model that shows the camera, adapter and eyepiece arrangement. [Autodesk DWF file, 58 KB].

The metalworking process may be illustrated by the first such adapter I made was some years back. This was for a Sony DSC-S30 digital camera, mounting to a Bausch and Lomb microscope. This creates a system for high-quality, wide-field photomicrography.

The lens of the Sony DSC-S30 camera provides a 37 mm inside diameter x 0.75 mm inside threads, and the microscope eyepiece provides a smooth 1.138 inch outer diameter cylinder. Thus the adapter will consist of a turret with outside threads to mate to the camera lens, and an inside bore to slip snugly over the microscope eyepiece.

The first dimensional step is to turn down the cylinder, leaving a raised ridge of 37 mm diameter, ready to take on the outside threads. I chose to thread a length of 5 mm, which was about twice the length of the inside threads on the camera turret. Using the threading bit to turn the smooth diameter makes it easy to leave 60 degree bevels on all the stepped edges. I was happy to find that the 0.75 mm metric thread pitch is available on the minilathe using the standard set of change gears (see the Yahoo 7x10minilathe group files area for tables of using change gears for metric threading). The photos show the work progressing on an aluminum billet I made as a casting experiment, and the casting flaws show up as dark spots or flecks. For later versions, I have been using aerospace grade aluminum stock.

Next I mounted the tailpiece onto the lathe with a drill chuck and 1/2-inch drill bit, and bored a hole into the center of the piece.

With that 0.500 inch starter hole drilled, I was ready to start boring out the 1.138 inch inside diameter that would receive the microscope eyepiece. For this I used carbide boring bar bits that reached the 1" depth of the finished part. (Making the boring bar tool holder is the subject of another of my project descriptions.) After boring the hole a few thousandths oversize, I had a close fit of the adapter to the eyepiece. I finished the part by cutting it from the cylinder using a parting tool. I cut a length that maximized the fitted depth, but still let the camera lens come to rest on the eyepiece. The photo shows the finished adapter.

Below is a view of the Sony DSC-S30 camera, with and without the adapter mounted.

This is an old Bausch and Lomb inspection microscope. This US-manufactured item isn't made any more, but when new they sold for about $2000. The optics are superb, providing a wide, flat field at a variety of zoom magnifications from 7x to 30x. Today, you can find them used on eBay for perhaps $500 or less, or you can buy a similar imported item for about that price new. The turrets of the binocular eyepieces have the virtue of being smooth, even aluminum cylinders. This allows a simple cylindrical adapter to nest on top of the eyepiece.

This is the camera mounted on the microscope eyepiece. The adapter aligns and rigidly fixes the camera to the microscope. The camera lens protrudes in such a way as to touch the eyepiece, so I should apply a bit of vinyl tape as a cushion, or perhaps machine a spacer ring to insert as a standoff. I may add winged setscrews in the future to lock the camera on the eyepiece.

This shows the camera turned on, with the camera display imaging the the microscope's magnified view of a coin. The optical system of this camera is well-matched to the exit pupil of this microscope. By adjusting the camera zoom one can either get a vignetted photo of the full field of the microscope, or a full-framed photo of the center region of the microscope view. Both modes are desirable for various purposes. The photo below shows the full-frame mode.

This is a portion, at full resolution, of a photo taken by the Sony camera in the above setup. The object shown is a Lincoln penny, of which you are seeing part of Lincoln's face. I measured the features shown with calipers, giving a true height of the representation as 0.070 in. The digital image is 526 pixels high. Thus the system resolves about 7500 pixels/inch, which is 7.5 pixels/thousandth-inch, 130 microinches/pixel, or 3.4 microns/pixel. If we assume your display renders 96 pixels/inch, then the effective magnification is about 78x (= 526 pixels / 96 pixels/in / 0.070 in). The camera resolves 1472 x 1104 pixels (not much by today's standards), so the camera and microscope can photograph a physical area of about 0.2 by 0.15 true inches at this level of detail; the full field to the eye view in the microscope is about a 0.25 inch diameter circle. The microscope field zooms from about 1 inch at 7x magnification, to 1/4 inch at 30x. This is an amazing quality of result given that this camera sells for under $200, and the microscope sells used for about $500. Such a system would have cost many $1000s, and required costly film processing, not many years ago. I don't know the resolution limits of the microscope optics, but they're probably better than what the Sony DSC-S30 camera is resolving in this setup. If that is true, then a higher-resolution camera would resolve more detail. I have a much better digital camera now, but it uses a large-aperture lens that isn't as well-matched to the microscope aperture, resulting in a severe vignette in the image. As a general optical design principle, one would want a small camera lens for this kind of behind-the-eyepiece microscopy. With camera lenses, bigger is usually better, since you can gather more light. But digital cameras can (and typically do) have very small, but nevertheless high-quality, lens systems, because the CCD electronic imaging devices are so much smaller than film formats. The light available is determined by the microscope optics, not the camera. Many digital cameras today (2004) seem to be using imaging chips and lenses that are very close to the human eye in physical scale. This is a wonderful thing for those wanting to adapt the cameras to microscopes, because no optical adapters (such as a negative "relay lens") are needed, just mechanical arrangements. The pupil of the human eye may be assume to be about 4 to 5 mm in diameter when viewing microscope images. A good microscope will provide an exit pupil of similar diameter, and the camera lens should match this as well. Not so wonderful for the would-be photomicrographer is the trend away from putting filter mount threads on the lens turrets, even on the more expensive consumer models; later versions of my Sony DSC-S30 have a telescoping lens contraption that regrettably features no thread mount. If you're looking to buy a digital camera with hopes of photomicrography, look for one with a fixed, threaded turret, with the inside thread diameter significantly larger than the microscope eyepiece you hope to use. Even if your camera has an extending/retracting lens turret, you may find an optional adapter tube (see Nikon, Canon, and Olympus examples below) that provides both room for the turret and filter threads for a further adapter. As a last resort, one can fit a sleeve machined just larger than the turret, with one or more screws for clamping to the turret itself.

The original microscopy experiments above were done in 2002. In 2004, I repeated them with the same microscope, but using a higher-resolution camera (Sony DSC-F707, 2560 x 1920 resolution = 5 megapixels) and an Edmund Scientific Co. resolution test target (gratings from 5 lines/mm to 200 lines/mm). This apparatus proved a resolution of 160 lines/mm (4000 lines/inch), or equivalently to 8000 pixels/inch (3 microns/pixel). The photograph shows a contrast enhancement of the 160 lines/mm grating. This is about the same resolution achieved directly viewing into the microscope eyepiece with the naked eye, and is the essential resolution limit imposed by the inspection microscope. Thus a higher-resolution camera does not necessarily translate into higher resolution photomicroscopy images, because the microscope itself introduces the resolution-limiting optical elements. This is a proper approach to the task, where the camera should be chosen to capture an image of some specified area, consistent with the resolution limits and field size of the microscope.

The advantage of a better camera is chiefly the larger field size it can capture at the resolution limits. To the left is a thumbnail of another Lincoln penny image taken with the higher-resolution camera at something less than the maximum magnification. See the full 1600x1600 resolution image here [155 KB JPG file], which makes a 20X image on a typical 96 dpi monitor. We can see a field of up to 0.9 inches diameter at this resolution (2000 pixels/inch), with the whole item imaged at once instead of just the nose. Using combinations of the camera and microscope zoom lenses, the magnification can be increased by another factor of about four to 80X or so, but vignetting will start to reduce the size of the object area.

The Sony DSC-S85 camera with the Sony VAD-S70 adapter (45mm to 52mm lens adapter) provides a 52mm filter thread.

Here are some more digital camera microscope adapters I made for a customer. These slide over a slightly smaller 1.135" eyepiece on a Bausch and Lomb microscope. The smaller item on the left provides an M41x0.5 thread for an Olympus C-3020 digital camera. The larger item on the right provides an M62x0.75 thread for an Olympus E-10 or E-20 digital camera. I used commercial 6061 aluminum round stock for these. The threads on the left look uneven because of an interference pattern (moire effect) on the digital photo. Note the optical illusion which makes the bore look larger on the left adapter compared to the right; they are in fact equal.

The photos below show the attachment of the M41x0.5 adapter (above on left) to an Olympus C-3020 digital camera, and to the microscope eyepiece.

This adapter I made for a customer with a Nikon Coolpix 5700 digital camera (reviewed here and here) and a Nikon Labophot microscope. That Nikon camera is unusual because although it is a rather advanced model, the zoom depends on the lens turret extending various distances in and out of the camera body, like many snapshot cameras. While the lens hood provides a threaded ring, because of the turret extension, you cannot mount a filter or adapter directly to those threads; instead you must use a Nikon UR-E8 adapter (shown in the photos), which is essentially a 34mm long step-down tube from male M53.5-0.75 (mates to lens hood) to female M50x0.75 (for further accessories). This tube has an ID=51mm and OD=55.75mm, with a stop ridge of 47mm ID at 5.5mm inside of the female threads. This is the black item in the photos. The aluminum microscope adapter I made mated to the M50x0.75 thread on the UR-E8 adapter and received a 23mm (OD) Nikon Labophot microscope eyepiece via a slip fit, overall length of 1 inch. After taking these specimen photos, I enlarged the 23mm bore to 29.2mm to slip over the external diameter of the Labophot eyepiece.

Another unusual feature of this adapter is that it can be screwed inside the UR-E8 adapter, or reversibly outside, depending on the camera lens turret extension. This allows the microscope eyepiece a 1.75-inch vertex range relative to the camera, to accomodate various zoom settings while minimizing vignetting. The photos to the left show the reversible mounting.

I made a similar large adapter, with nylon thumbscrew, to adapt a Nikon D70 digital camera with a 70-300mm zoom lens and 62mm lens thread (M62x0.75), to a Celestron 4060 microscope eyepiece with a 1.100" outside diameter.

This step-down ring adapter (shown in the center of the photo) I made for a customer who already had a Canon LA-DC52C step-up adapter (left of photo) for a Canon A60, A70, A75, or A85 digital camera (similar to the LA-DC52D for the A80 or A95, or the LA-DC52B for the A30 and A40), which provides an M52x0.75 thread, which was to be mounted to a C-mount (1"-32 thread) adapter (right of photo) on the microscope. This Canon adapter, like the Nikon one above, provides an offset tube, inside which the lens turret of the camera has room to extend and retract. Both the inside and outside edges of the ring are threaded, although the photo resolution doesn't resolve all the threads.

This adapter is different than the others in that instead of an unthreaded sliding fit to a cylindrical microscope eyepiece, the adapter provides a female thread to connect to C-mount threads on the microscope. It is essentially a 1/4" thick aluminum washer with threads on the inside and outside edges.

A similar approach would work for the Canon LA-DC58D conversion lens adapter, which provides a 58mm filter thread for the Canon Powershot G6 camera. Likewise for the LA-DC58 for the Powershot G1 and G2, and the LA-DC58B for the Powershot G3 and G5.

This adapter I made for a customer's Olympus C-4000 camera, which provides a 43mm filter thread mount. The smooth inside bore slips closely over the eyepiece (1.162" outside diameter) of a Bausch and Lomb inspection microscope. The height in the photo shows my standard 1-inch overall length for these adapters.

I have also begun including a rubber O-ring with each of the slip-type adapters. For example, for this adapter with a 1.162" inside diameter, a standard inch-series #213 Buna-N O-ring (ID=15/16", OD=1-3/16", section=1/8") fits snugly into the inside diameter without distorting. This provides a cushion against which one can rest the front of the lens turret to achieve a near-minimal vertex distance to the eyepiece optics. To increase the vertex distance, one can insert more of the same O-rings in a stack.

This adapter also required an additional modification (not shown in the photo above or visible in the assembly photo below) to accommodate the turret lens of the camera projecting 0.050" beyond the end of the Olympus CLA-1 41mm-43mm adapter/extension tube for this camera. Since the step ending the 43mm female threads inside the Olympus tube was 0.115" deep, a total length of at least 0.165" (0.2" in practice) had to be relieved inside the threaded end of the adapter, with an inside diamter of 1.575" (40mm) to allow passage of the 1.45" dia extending lens turret.

This photo shows the completed assembly, consisting of the Olympus C-4000 camera, Olympus CLA-1 adapter, and custom microscope adapter.

Most camera filter threads have a tiny 0.75mm spacing ("pitch"). This close-up photo shows a threaded section of the C-4000 adapter above. Threads cut properly on a lathe wiil have a smooth finish and correct profile. Good-quality threads attach easily to the camera lens, and ensure a secure attachment.

I usually design the threaded length to span about 1/4", which is about 8 to 10 fully threaded turns, like you see here. Full engagement to the camera lens typically requires only 2 or 3 careful turns. Should the initial threads of an adapter ever be damaged, such as by dropping it or accidentally cross-threading it into the lens, I can repair it on the lathe by simply facing off a bit of the threaded end, exposing new, undamaged threads at the adapter face.

This custom adapter connects the 37mm filter thread on the customer's camera to an American Optical (AO) inspection microscope 10X eyepiece having a 1.180" outside diameter. This adapter is a bit thin, but still strong enough for the mounting task. In cases where the camera threads happen to be smaller in diameter than the outside of the eyepiece, the adapter uses a shoulder to step up the body diameter and maintain strength.

This photo shows how the eyepiece joins precisely to the adapter with a slip fit. This provides an accurate axial alignment, which minimizes aberrations and distortions in the photo images. By having the customer send the actual eyepiece, a very close fit is guaranteed on the first try.

These slip fits are designed to be close enough for a "telescoping" fit between the eyepiece and the adapter, allowing an adjustable range of vertex distance. The adapter can be fixed on the eyepiece by assembling with a bit of tissue paper or other thin shim for a tight fit. Or, a bit of white glue or cyanoacrylate (CA) glue ("super glue") into the gap creates a semi-permanent attachment; since CA glue does not bond strongly to the oxidized aluminum surfaces of the adapter and eyepiece, the bond is more of a wedge casting than a true glued bond, and the pieces can be later separated and the glue cleaned off if needed. We can also add an optional 1/4"-20 threaded hole and nylon thumbscrew to the adapter as a clamp.

This custom adapter mounts a Nikon 4500 digital camera with 28mm threads to an Olympus SZ-CTV microscope adapter. The Olympus adapter provides a cylindrical slip fit with a thumbscrew.

This custom adapter mounts a Nikon Coolpix 950 digital camera with 28mm threads to a Leica microscope eyepiece with 1.126" outside diameter. This is an unusual adapter in that the eyepiece diameter exceeds the camera threads, requiring a stepped shoulder on the adapter.

This custom adapter mounts an Olympus C-750 digital camera (via the 55mm Olympus CLA-4 adapter tube) to a cylindrical microscope eyepiece.

These custom adapters are threaded bushings, with C-mount (1"-32) threads on the outside, and 1/4"-20 (UNC coarse) threads on the inside. Lengths are 10mm and 14mm. The cost of a small item like this by weight roughly equates to gold. Precision instrumentation is not cheap.

Here the same two adapters are reworked to 1/2"-20 (UNF fine) inside threads, with a third adapter of 16mm length.

This custom adapter mounts a 37mm camera thread (M37x0.75) to a 1.310" outside diameter cylindrical Bausch & Lomb inspection microscope eyepiece. Note the use of a fitted O-ring as a cushion for the front of the camera lens, which minimizes the reflex distance and vignetting. We provide the correct O-ring(s) as needed with the adapter.

This custom adapter mounts a 30mm camera thread (M30x0.75) to a 1.152" outside diameter cylindrical Bausch & Lomb inspection microscope eyepiece. This mounts a Sony DCR-TRV11 or DCR-TVR27 video camera to the scope.

This custom adapter mounts a 37mm camera thread (M37x0.75) to a 1.221" (31mm) outside diameter cylindrical Nikon CoolPix MDC lens (a relay lens for a Leica MZ16 and other microscopes, also called an MDC-A or MDC-relay, presumably just an acronym for "microscope digital camera" [adapter]). The close-fitting smooth inside bore of the adapter provides a telescoping mechanism which with the single nylon clamping screw (1/4"-20 x 1 inch) provides an adjustable vertex distance between camera and microscope. Male threads (M28x0.75-3mm) at the end of the MDC lens are not used; a fixed step-up ring (28mm to 37mm), a standard item from photographic suppliers, is an alternative for a fixed-vertex-distance adaptation.

The custom adapter (on the right in the photo) is a threaded-flanged bushing which adapts the 28mm (M28x0.75) female thread of the Nikon UR-E6 adapter (on the left in the photo, for a Nikon Coolpix 5000 digital camera) to a female C-mount thread (1"-32) for attachment to a microscope lens. The flange allows one or two O-rings to be inserted to adjust the vertex distance. This bushing weighed only 3.6 grams, and the inside and outside threads cleared each other by a thickness of less than 1mm. The finished item was priced at about 3 times the cost of gold by weight.

This custom adapter mounts a Canon EOS Digital Rebel 300D digital SLR with 18-55 EFS lens (58mm camera thread, M58x0.75) to a 1.154" (29.3mm) outside diamter microscope eyepiece, namely a Leica Mark X Gemolite Stereo Zoom with 15X W.F. eyepieces. The three nylon screws (1/4"-20 x 1-inch) allow for vertex distance adjustment.

Topcon SL-5D and SL-6E Slit Lamp

This custom adapter retrofits Canon and Nikon digital SLRs to the camera port of an ophthalmological instrument, a Topcon slit lamp (Topcon SL-5D slit lamp and Topcon SL-6E slit lamp). The camera port in the original design accepted an obsolete Topcon 35mm film camera back. This photo shows the original bayonet ring mount for the original film camera.
This drawing shows the new adaptation for the Topcon SL-5D and SL-6E slit lamps, consisting of a custom adapter which replaces certain components in the original bayonet mount, and a stock T-mount adapter for the Canon or Nikon digital SLR. The custom adapter provides a male T-mount thread (M42x0.75), on which a commerical adapter (T-mount to EOS) is then attached for the camera. The design works with the original Topcon locking ring to secure the adapter into the instrument. Adapting in two pieces via an intermediate T-mount thread has several benefits: it avoids having to machine the more difficult EOS bayonet lens fitting, it allows rotation of the camera on the instrument, it provides an adjustable vertex distance; and it is compatible with many other T-mount items. The T-mount-to-EOS ring can be purchased inexpensively off-the-shelf, as well as for a wide variety of other camera lens standards. See the detailed mechanical drawing [3.5 MB PDF file] for complete details and specifications.
A photo showing the upgraded camera coupler mounted in a Topcon SL-5E slit lamp, ready to receive the digital camera. The camera coupler locks into the Topcon instrument using the original locking ring and handle seen just below the camera bayonet mount.
A photo showing the Canon 400D (Rebel XTi) digital SLR being mounted on the Topcon SL-5E slit lamp, using the adapter. Close coupling of the new camera to the instrument maintains parfocality with the eyepiece view, while not interfering with the observer's chin. The digital camera can be quickly removed and a conventional lens attached for use in ordinary photography. Besides the Canon 400D (Rebel XTi), the Canon 300D (Digital Rebel), 350D (Digital Rebel XT), and 450D (Digital Rebel XSi) models are also suitable for this application.

Topcon TRC-50EX Retinal Camera

This adapter couples a Topcon TRC-50EX retinal camera to a Canon 400D digital SLR. It is complex, consisting of optical, mechanical, and electrical components. See the installation and operating instructions for more diagrams, photos and details. Five optical elements in two groups resize and relocate the instrument exit pupil at a suitable distance for a relay lens, which in turn refocuses the image at a size to match the camera's digital sensor, which is 0.6 the size of the original 35mm film intended for the instrument. Mechanical components maintain a rigid positioning of the optics, as well as axial and rotational adjustments for focusing and alignment. The electronic interface cable (not shown) operates the digital camera synchronously with the instrument triggers.

This photo shows the adapter mounted on a Canon 400D digital SLR camera. Besides the 5 optical elements, the adapter consists of 4 custom and 2 stock mechanical assemblies.

Here's the adapter and camera mounted on the Topcon TRC-50EX. We have used the upper port which the Topcon TRC-50EX provides for mounting an accessory camera. To take a photo, the operator pushes a button on the instrument joystick to trigger a synchronized series of events: First, an instrument mirror flips to redirect the image from the viewfinder eyepiece to the upper camera. Second, the instrument sends an electronic signal to the digital camera to open the its shutter. Third, when the digital camera has opened its shutter, it returns an electronic signal to the instrument to fire the flash illumination. Fourth, the instrument fires the flash. Fifth, the camera shutter closes. Finally, the instrument returns the mirror to the viewfinder path. The custom cable which connects the digital SLR's shutter release and flash sync to the Topcon instrument is not shown here.

Topcon TRC-50VT Retinal Camera

This adapter kit converts a Topcon TRC-50VT retinal camera (also known as a fundus camera) from the original film camera back to use a Canon EOS digital SLR camera. The kit consists of:

A mechanical adapter to mount the Canon digital camera on the Topcon instrument in a precisely parfocal, axially centered position. A modified breech ring that replaces the original Topcon ring, which avoids the mechanical interference of the flash "nose" of certain Canon SLR models with the instrument. An neutral-density filter for the Topcon instrument, which reduces the instrument's flash intensity to compensate for the Canon digital SLR's improved light sensitivity. A flash synchronization adapter cable, which triggers the Topcon instrument flash in synchronization with the Canon digital camera shutter. This cable adapts the Canon digital camera flash trigger signal to the DB-15 connector provided on the Topcon TRC-50VT, which was originally intended for a Polaroid camera.

See the mechanical drawing [700 KB PDF file] for a detailed view of the adapted camera mounting.

There are 3 options I build for the Topcon TRC-50VT:

1. Direct projection to a Canon 400D (aka Digital Rebel XTi) or Canon 450D (Digital Rebel XSi) on the rear port,
2. Direct projection to a full-frame Canon 5D on the rear port, and
3. Relay lens to a Canon 400D on the upper port.

Option (1) imposes an 0.6X crop factor, so you lose some of the top and bottom of the image, both in viewing and in imaging. Options (2) and (3) don't crop, they show the full frame.

Options (1) and (2) mount the digital camera on the rear port, close to the instrument like the original film camera. Option (3) mounts the digital camera above the top of the instrument on the upper port, similar to the optional Polaroid or TV attachments Topcon originally sold for the instrument.

Options (1) and (2) show an inverted preview, which you either get used to, or use my inverting Canon viewfinder magnifier, which adds 4 inches of length the rear of the camera. These options also eliminate the Topcon viewfinder as a consequence of using the rear port. The Canon viewfinder is a focusing-screen type with a beamsplitter for autofocus and exposure metering, which is necessarily smaller and less bright compared to the original Topcon viewfinder eyepiece with its near-100 percent transmission. You typically have to boost the steady illumination to compensate with difficult subject eyes compared to the Topcon film camera viewfinder, which adds another difficulty factor in itself to marginally viewable subjects. Viewfinding for fluorescein angiography (FA) is thus hardly possible, since the views are so dim even in the Topcon viewfinder.

Option (3) retains the Topcon film camera for viewfinding, with the digital camera acting as an image recorder only. This configuration performs with the same superb clinical convenience of the original design. The chief disadvantage is the higher cost. A secondary disadvantage is that it relies on the mirror-flip mechanism for the upper port, which has proven trouble-prone in the aging Topcon film-based instruments.

The electronic interface is the same for all three options.

Other model Canon cameras such as the Digital Rebel series, and the 10D/20D/30D/40D series, are compatible with options (1) and (3).

Canon Viewfinder Magnifier-Inverter

This viewfinder magnifier (see detailed description page) for Canon digital SLR cameras is a custom telescopic component I make, which provides a 2X magnified and inverted enlargement of the standard viewfinder. This is designed to compensate for the inverted view resulting from adaptation of certain instruments, such as the direct coupling to a Topcon TRC-50VT retinal camera described above.

Topcon TRC-JE and TRC-FE Retinal Cameras

This custom adapter retrofits a Canon EOS 20D digital camera to the camera port of a Topcon TRC-FE or TRC-JE fundus camera. This approach to the problem disassembles the bayonet mount from the old film camera, to which we fit a custom T-mount threaded adapter, following the original bolt-circle screw pattern. To the T-mount threads, we finish with an off-the-shelf T-mount-to-EF Canon mount adapter. These three parts combine to connect the fundus camera optics to the EOS 20D digital camera. You can browse: 

A 3D model of the assembled Topcon camera bayonet, custom adapter, and EOS adapter [113 KB Autodesk DWF file, free viewer], An isometric close-up exploded view [54 KB GIF image], and A mechanical drawing [77 KB PDF file].

 Click image to enlarge Since this adaptation increases the focal plane distance, it does not preserve the parfocal operation of the instrument. An updated version (not shown) moves the camera closer so as to maintain parfocality.

This thin threaded bushing adapts a 2"-40 threaded instrument to a M58x0.75 lens thread. Note the split ring design which prevents seizing of the small pitch inside threads on the large outside diameter instrument. Note also the small dimples (1/16" diameter x 1/16" deep) for a spanner wrench tool to insert and remove the adapter.

This is a custom adapter for a 1.162" outside diameter Bausch & Lomb eyepiece to C-mount (1"-32) lens thread.

This is a custom adapter for a 1.25" outside diameter telescope eyepiece to an M50x0.75 lens thread. Opposing nylon thumbscrews lock the eyepiece in position, while allowing vertex distance adjustment.

Selecting a Camera for Digital Photomicrography

I've had inquiries about what "consumer" or "prosumer" digital cameras are good for adapting to photomicrography. Some criteria of desirability are:

• Accessory threads that permit flush mounting of an adapter: Most current digital cameras such as the compact consumer types don't have them. Some cameras with turret type lenses have threads or a bayonet fitting on the camera body which accepts a special adapter which surrounds the turret with a tube that terminates in standard filter threads; this is an acceptable compromise.
• Optical dimensions close to the human eye: This permits a direct optical path for through-the-eyepiece coupling, and avoids vignetting. See the section on Understanding and Avoiding Vignetting below. Large lenses, such as are found on better snapshot cameras and SLRs, introduce unavoidable vignetting in afocal photomicrography; such camera lenses can only be adapted with a photo eyepiece, which is a more expensive adapter incorporating optical elements. Less-expensive cameras tend to have the appropriate size lens in a turret form.
• Manual modes for aperture and shutter: Afocal photomicrography typically requires that the aperture be manually fixed, since wider aperture sizes may introduce vignetting. Manual shutter control is not strictly necessary, but it is convenient for adjusting the exposure of difficult microscopic scenes. Most inexpensive digital cameras do not have a manual mode for aperture and shutter.
• Manual mode for focusing: Most inexpensive digital cameras do not have a manual focusing mode. A semi-manual focus is sometimes available as a menu setting to set a fixed focus at infinity, which is what is actually needed, so this is acceptable.

What cameras sold today are suitable? Cameras at very low cost (less than USD $200) have become available which meet all the above desirability criteria. The Canon A630 is an example of an ideal camera for digital photomicrography. It also provides a live video-out preview, so you can then attach a video monitor to your instrument. Canon changes models very frequently, and in mid-2008, the A-series models with suitable features are the following:

Canon A-Series Cameras Suitable for Eyepiece Photomicrography Model list updated as of May, 2008
Canon Model (Note 1)	Articulated LCD screen	Remote Capture (Note 2)	Live Video NTSC/PAL	Canon CLA tube	Aftermarket CLA tube(s)
Canon A510	No	Yes	Yes	LA-DC52F	Bower A52B510C Sakar JA-A80-52
Canon A520	No	Yes	Yes	LA-DC52F	Bower A52B510C Sakar JA-A80-52
Canon A540	No	No	Yes	LA-DC52F	Bower A52B510C Sakar JA-A80-52
Canon A570 IS	No	No	Yes	LA-DC52G	Sakar JA-A570-52
Canon A580	No	No	Yes	LA-DC52G	Sakar JA-A570-52
Canon A590 IS	No	No	Yes	LA-DC52G	Sakar JA-A570-52
Canon A610	Yes	No	Yes	LA-DC58F	Bower A52B610C Sakar JA-640-52
Canon A620	No	Yes	Yes	LA-DC58F	Bower A52B610C Sakar JA-640-52
Canon A630	Yes	No	Yes	LA-DC58F	Bower A52B610C Sakar JA-640-52
Canon A640	Yes	Yes	Yes	LA-DC58F	Bower A52B610C Sakar JA-640-52
Canon A650 IS	Yes	No	Yes	LA-DC58J
Canon A700	No	No	Yes	LA-DC58G
Canon A710 IS	No	No	Yes	LA-DC58G
Canon A720 IS	No	No	Yes	LA-DC58G
Canon G7	No	Yes	Yes	LA-DC58H
Canon G9	No	Yes	Yes	LA-DC58H
Canon models A470, A530, A550, and A560 are not suitable (lens-adapter bayonet omitted) Likewise all SD and SX models.
Older Canon models A80 and A95 are suitable via the LA-DC52F CLA tube

Note 1: Don't be confused by the "IS" designation in the Canon model number; this is just a redundant emphasis that that the model features image stabilization. For example, you may see the Canon A650 camera referred to as model "A650 IS" or just "A650"; these are the same thing.

Note 2: Remote capture requires a software application for the PC. Canon includes a basic remote capture application with the camera. Breeze Systems publishes PSRemote for $49 (USD).

The articulated LCD screen is a useful feature if the camera must be mounted at an angle that does not permit convenient viewing towards the rear of the camera body. Remote capture which allows you to operate the camera tethered to a PC, which can be an important feature for applications like laboratory data capture. A video-out feature allows you to display the live (although low-resolution) microscopic image on a video monitor or PC, such as for group instruction.

You may also wish to study the eyepiece adapter instruction sheet provided with my eyepiece adapters for the Canon A-series cameras.

For laboratory use, it is often necessary to have direct PC control of the camera, and/or image transfer, via protocols over USB connections like PTP (Picture Transfer Protocol). This allows periodic or time-based taking of photos, or synchronization with other laboratory apparatus or sensors. See Figuière's excellent page on Digital Camera Support for UNIX, Linux and BSD.

Understanding and Avoiding Vignetting

The "Ramsden disc" (also called "Ramsden circle") produced by the microscope eyepiece is the circular field image formed some distance (the vertex or eye-relief distance) above the top of the eyepiece. A good eyepiece forms a Ramsden disc equal to or larger than the size of the pupil of the human observer's eye. The human pupil varies in size with lighting and the observer's age, so the Ramsden disc should be designed somewhat larger than the largest eye pupil, which means that the eye (and the eye's pupil) can move about without cutting off some of the eyepiece image.

The size and axial location of the Ramsden disc is also called the "exit pupil" of the eyepiece. The exit pupil is a critical characteristic for analyzing any optical system, and especially important when coupling two optical systems to each other, such as the eye to the microscope, or a camera to the microscope. To avoid vignetting, the corresponding entrance pupil of the camera must be equal to or smaller than the eyepiece exit pupil, and the camera entrance pupil must be positionable within the eye-relief distance. You can think of the eyepiece exit pupil as a projected map (not really an image) of the microscope field of view, and the camera's entrance pupil as a map of the camera's digital image sensor (or film frame in the old days). To avoid vignetting, these two maps must overlay each other by having the same size and by locating in the same position along the optical axis. This achieves the goal of connecting the camera's field of view with the field of presentation of the eyepiece, and matching these two fields with the same angle.

If these two pupils are mismatched, either being different sizes or different axial locations, the camera will see a vignetted image. Vignetting appears as either "too far" (the camera "sees" only the center of the field, because an aperture in the eyepiece masks the edges) or "too close" (the camera can potentially "see" the whole field, but the image sensor crops the edges). This is rather like an impedance matching problem in electronics.

The axial distance constraint is typically incompatible with a camera lens that establishes an entrance pupil deep within the lens itself, which is typical of large complex lenses such as are found on DSLRs. The eyepiece "eye relief" (distance of the eyepiece's exit pupil from the last surface of the eyepiece, 20mm or so typical) is designed to be long enough to at least reach through the human cornea and anterior chamber of the eye to the iris, which constitutes the eye's entrance pupil. An eyepiece with a generous eye relief will provide enough of this distance to allow you to wear eyeglasses and still place your iris up to the exit pupil of the eyepiece.

When imaging with a camera instead of the human eye, this same eye relief must reach far enough into the camera lens to reach the camera's entrance pupil. That is, the eyepiece provides ample "eye relief" for human eyes, but this may or may not be enough "relief" for the camera lens system. Some cameras have lens dimensions and entrance pupils similar to the human eye, and thus are well-suited to afocal photomicrography because the eyepiece exit pupil can reach the camera entrance pupil, and the pupils are of similar size.

Other cameras, especially expensive DSLRs with big lenses, are severely mismatched in this regard, and impose intolerable vignetting. The entrance pupil of a large camera lens is typically itself large and/or deep within the lens body, in comparison the scale of the human eye. In terms of typical dimensions, a typical 10X wide-field eyepiece exit pupil is sized as a disk of about 10mm diameter floating about 20mm above the eyepiece, while a typical large camera lens has an entrance pupil 35mm or more in diameter, located 50mm or so inside of the first glass surface. While the f/stop setting of the lens can shrink the camera's entrance pupil, and the zoom adjustment can move the entrance pupil somewhat foreward and back, there is typically not enough range of freedom to provide a match. Think of it as a horse or a whale trying to look into your microscope; their large eyes would see a vignetted image in a human-scale eyepiece that is too small for their eyes.

If the camera lens can't be changed (which is the case with consumer type cameras that have permanently mounted lenses), the most practical thing is to replace the stock microscope eyepiece with a gigantic, wide-field, low-power, eyepiece. Such an eyepiece provides a very large exit pupil, very long eye relief, and insensitivity to lateral pupil shift. This is the approach of my latest design for a custom fitted adapter with 30 or 50 mm diameter symmetric lens aperture. The disadvantages of the "giant eyepiece" approach include the cost of this massive eyepiece, and that the size and weight of the resulting eyepiece-camera combination tend to overwhelm a typical microscope, requiring some type of auxiliary mechanical support. Some older microscopes correct objective aberrations in the eyepiece, and this correction is not feasible in a reasonably-priced custom eyepiece.

Note that for a compound microscope, vignetting can arise only between the eyepiece and the camera. The microscope objective has no role because all the limiting apertures are imposed in the eyepiece, such as the crisp edge-of-field stop, or the reticle if so equipped. Conveniently, this means you can shop for a compatible camera for your microscope by taking nothing but your loose eyepiece in hand to the camera store. Line the eyepiece up close to the lens of any and all cameras on display to see which cameras are compatible and which will vignette with various camera zoom settings. Leave the bulky microscope at the lab.

"Vignetting" is a broad effect in optics that involves more than just instrument-to-camera couplings. We have been using the word "vignetting" to describe an undesirable mismatch of camera to instrument, resulting in either a loss of some of the instrument's field of view, or a failure to fill the camera's field of view, or both.

Another sense of the word "vignetting" involves the unavoidable darkening of image fields at the edges due to natural or optical principles. For example, natural vignetting is the effect in multi-element lenses of the entrance pupil being gradually blocked by prior apertures at angles off the optical axis, which can be avoided altogether in a careful lens design, but is typically tolerated as a compromise in wide-angle or zoom lenses. This effect is observed as a drop-off in brightness at the edges of an image, and as the gradual distortion of off-center out-of-focus-highlights from round into a cat's-eye shape.

Vignetting is discussed in some optical textbooks under the "Theory of stops" (Jacobs, Fundamentals of Optical Engineering), "Effects of stops" (Jenkins and White, Fundamentals of Optics), or "Stops and apertures" (Smith, Modern Optical Engineering).

Yet another sense of "vignetting" is a certain fundamental optical limitation: optical vignetting is the unavoidable drop-off in intensity at an image field by the fourth power of the cosine of the angle of incidence (the cosine⁴ falloff). Using the term "vignetting" for this effect would seem to be a misnomer, since this falloff has nothing to do with stops and is unavoidable. Since the visual appearance resembles vignetting due to stops, the term has nevertheless been applied.

"Vignetting" is of course also a style of the photographic arts, where stop-induced vignetting is deliberately applied to a photograph. The edges of a portrait or scene become gradually darkened or washed-out, enhancing the composition with a tunnel-vision effect.

Understanding C-Mount and CS-Mount Standard Mechanics, Optics, and Cameras

You may also wish to study the C-mount adapter instruction sheet provided with my C-mount products.

Smaller mounting standards include S-mount (M12x0.5 thread) and X-mount (M10x0.5 thread). I have also seen reference to a Sony NF-mount, which appears similar to C-mount, but with an M17x0.75 thread projecting 4mm, and a 12mm flange distance.

C-mount adapter plate

This photo shows my manufacture of a customer's design for a C-mount adapter. This 2-part assembly accepts a C-mount lens and mounts it to a flat detector face. The knurled, threaded bushing provides fine adjustment of the focal plane position.

EF to C-mount adapter

These photos show my design for an EOS lens to C-mount adapter. This adapter converts any Canon EOS camera lens into a C-mount lens. This adapts the Canon EF lens mount to C-mount while maintaining parfocality and infinity focus. The adapter consists of two parts; one is the EF body mount (bayonet receptacle) and the other is the male threaded C-mount fitting.

Here we see how the adapter attaches to a typical high-quality Canon EOS camera lens, the Canon EF 28-135mm f/3.5-5.6 IS USM lens. Of course the Canon lens must be used with manual focus and aperture settings for the C-mount application.

A similar adapter could be made to convert any Nikon F mount or Four-thirds mount lens to C-mount. Older lens mounts such as Minolta and Pentax K can also be fitted. Obsolete but high-quality film camera lenses (which are now inexpensive surplus items) can thus be applied to C-mount instrumentation.

Understanding Standard Filter Threads and Adapters

Filter thread sizes are important to microscope adapters, because it is often much cheaper to make a custom adapter with a larger thread size than the camera provides. This is due to the difficulty of machining precision threads up to a shoulder, versus machining threads on the outside of a cylinder without a shoulder. The larger cylindrical adapter can then be adapted in turn to the camera's smaller thread size by using an inexpensive, off-the-shelf step-up ring.

Filter threads are not standardized (other than holding to a metric form of arbitrary nominal size), but over the years camera manufacturers have come to mostly use a limited set of whole-millimeter sizes. While it would have been economical to have a thread series such as is standardized for bolts, the industry never came to any agreement over this issue, and consequently adapting filter threads from one size to another is not always possible without a custom-machined item. The most commonly used filter threads are the 0.75mm pitch of the diameters in the following table. You are most likely to find inexpensive off-the-shelf step-up and step-down rings which directly or in combination adapt these sizes. In other words, you can make an inexpensive adapter from any one of these sizes to any of the others, usually in one step or two steps.

Of the above sizes, 37mm is very common on consumer video camera lenses, and 58mm is very common on SLR camera lenses.

The following are less common sizes for you which you may find an off-the-shelf step-up or step-down ring to one of the above sizes, from which you can get to any other common size, in one or two more steps.

If you have to fit a size not listed above, chances are you will not easily find an inexpensive adapter.

Since inserting a ring adds a few millimeters of axial length to the optical system, a single ring or combination of these rings may insert more than an acceptable length to the adapter. In this case there is no option but to eliminate the step rings by fabricating the target thread directly on the custom adapter, even though this may amount to an added cost.

If for some reason you need to add length to a filter-thread system, there are also extension rings sold, which are essentially no-change step-up rings (equal size male and female threads), and which add a typical 5mm to the length. You can also mate a step-up and step-down ring to make a filter-thread extension ring. Yet another trick to make an extension ring is to remove the glass from an ordinary photographic filter or close-up lens, since the filter will have a male and female thread of the same size; on a good-quality filter this is a reversible modification accomplished with an optical spanner-wrench tool on a threaded ring. Old filters and close-up lenses are also a source of outside-threaded rings in standard filter thread sizes for making optical assemblies.

Note that the T-mount thread (42mm) and C-mount thread (1"-32tpi) not in either of the above series. Since these two threads are intended for camera lens mounts (mounting the exit end of a lens to a camera) instead of camera lens filters (mounting a filter on the entrance end of the lens), off-the-shelf adapters for them adapt things like camera bayonet rings, not filter threads.

Photo Eyepieces for Large Cameras

The photo at the left shows a typical photo eyepiece (mechanical drawing [256KB PDF file]) which I designed and fabricated to adapt a 58mm camera thread to a 23mm eyepiece tube. This will couple many digital SLRs (such as the Canon EOS series) to the most common eyepiece standard. The optics are a 4-element symmetric (Plossl) design optimized for microscopy. This item is $400. This prototyping-styled design provides thumbscrew locks for the optical components, which allows you to evaluate various optical designs by easily switching various lens elements. The production version of the design (version 2 below) uses coupled tubes and a spacing ring instead of thumbscrews.

This photo shows version 2 of the photo eyepiece for SLR cameras. The assembly is shown mounted on a Canon 400D (Canon Digital Rebel XTi) SLR camera, using the stock 18-55mm Canon lens that is usually bundled with this camera in retail stores. The photo eyepiece also works with other SLR makes such as Nikon.

This view into the eyelens end of the photo eyepiece shows the large aperture and short focal length needed to properly couple the microscope image field to the large camera lens with a proper crop ratio and without vignetting.

This side view of the assembly shows the mechanical arrangement of the two halves of the eyepiece. The top half is threaded to mate with the camera lens, possibly with a step-down ring if the lens filter thread is larger than the most common size of 58mm. The bottom half is sized to insert into a DIN-standard 23.2mm microscope eyepiece tube; another version (not shown) fits 30mm standard eyepiece tubes.

This view shows the assortment of custom components that make up the photo eyepiece assembly. The aperture and power of the optical elements are calculated to present an infinity view of the microscopic field in the field-of-view angle acceptable to the camera (which determines the crop ratio), and at an exit pupil which reaches into the entrance pupil of the camera lens (which eliminates vignetting). Fully-coated, achromatic elements are used to maximize image contrast and quality.

This drawing [768 KB PDF file] shows the mechanical specifications and features for the photo eyepiece. The design uses a T-mount intermediate so that it is readily adapted to other instruments or cameras that require an afocal image with a high exit pupil and narrow apparent field.

This drawing [623 KB PDF file, 1 page] shows an adapter which converts a Tektronix oscilloscope Polaroid camera hood (model XG) to use a digital camera. This hood constituted the front attachment for the Tektronix C-7 CRT camera auto-film system. The digital adaptation use the existing tapered and hinged hood from the old assembly, but replaces the Polaroid camera with a custom converter plate and custom threaded ring to attach a stock conversion lens adapter for a Canon A-series digital camera. By using the slowest ISO speed setting, macro focus, and wide-angle zoom, the digital camera takes a well-framed high-resolution photo of the oscilloscope screen, as shown in this sample oscilloscope screen shot taken from an ophthalmic ultrasound instrument.

This drawing [408 KB PDF file, 1 page] and the following photo show an adapter which adapts a digital camera to an American Optical (AO) microscope model 10, 110 or 120, or Reichert Microstar microscope, using the trinocular port. An 23mm eyepiece adapter also works on these microscopes when not equipped with a photoport.

This photo shows my latest design for an digital SLR camera to microscope adapter for 23mm eyetubes using the afocal mode. This is an afocal design which uses the stock 18-55mm lens sold as a kit with the Canon Digital Rebel SLRs. This adapter also works with the similar Nikon 18-55mm kit lens for the Nikon D40, D60, D80, D200 and D300. The zoom feature of the stock lens allows you to choose the cropping of the circular microscope field of view to the rectangular camera field, as described below under "Understanding Cropping".

This photo shows my latest design for a digital SLR camera to microscope adapter for 23mm eyetubes using relay lens projection. The adapter replaces the usual camera lens to couple the microscope to the camera. This is a more expensive adapter than the afocal type, because it involves more optical elements and mechanical structure. Having less glass in the optical path, however, the image quality is better than afocal adapters. The camera side of the adapter is a T-mount standard, meaning it works with Canon, Nikon, and Olympus (Four-Thirds) digital SLRs.

Understanding Cropping

In adapting cameras to instruments, "cropping" is always an issue, because the shape or aspect ratio of the field of view of the instrument rarely matches the field of view of the camera. Some compromised choice must be made of how to scale and overlay one field against the other. This choice of geometry is called the "crop", and is fixed by the optical scaling by the adapter of the instrument field onto the digital camera sensor.

The cropping describes how the circular shape of the microscope's field of view is fitted to the rectangular shape of the camera's field of view. Since these shapes do not match, the fields cannot be scaled and overlaid without leaving some of one or the other (or both) fields unused. The type of cropping is chosen based on the goals of the application. In choosing the cropping, one must evaluate whether it is better to not use part of the microscope field, versus not using part of the camera field, or some combination of the two. Depending on the application, this choice may be simply a matter of visual style, or it may be dictated by requirements such as having to see all of the microscope field (which dictates an inscribed crop) or having to use all of the camera field (which dictates an outscribed crop). On some adaptations, the crop is fixed by the adapter; on others a zoom lens on the camera is incorporated, so the user can change the crop by zooming between wide-angle and telephoto settings.

Inscribed cropping: The circular microscope field of view "inscribes" the rectangular camera field of view. This is the most commonly used crop, because it "looks" like a traditional microscope film photograph, and good digital cameras are able to capture all of the resolution of the image at this scale. While all of the microscope's field of view is captured in the photograph, the left and right sides of the photograph are unused area. With digital photography, the unused areas of the photograph can be filled-in during post-processing to be white or transparent instead of just black. Geometrically speaking, to establish inscribed cropping, the optics of the adapter scale the vertical aspect of the camera field to the diameter of the circular microscope field. Sometimes the scaling of the circular field may be deliberately shrunk to somewhat smaller than the vertical aspect, to allow for manufacturing tolerances in the optical and mechanical elements. This photo (also shown above for the adapters for American Optical microscopes) shows an example of a digital camera on a microscope with incribed cropping of the microscope field of view displayed on the camera's LCD viewer.

Outscribed cropping: The circular microscope field of view "outscribes" the rectangular camera field of view. This results in photographs which are completely "lit" without any black, unused areas, but the edges of the microscope field of view are not recorded in the photograph.

See these same descriptions and diagrams of cropping on a single-page drawing [79 KB PDF file, 1 page].

Links for Digital Photomicrography

• My drawing of frame sizes [PDF file] for 35mm film versus the Canon 400D digital camera versus a microscope 10X WF eyepiece field of view. This is helpful in analyzing how various imaging sources and detectors will result in cropped images. The diagrams show the original circular or rectangular field with inscribed and outscribed rectangles or circles. Printing this document at 1:1 scale will be true to the actual sizes, making it usable as a physical test pattern.

• Gregor Overney's "Introduction to Digital Photomicrography".

• Steve Durr's Introduction to Photomicrography.

• Paul James' Mounting digicams with zoom lenses over the microscope.

• Paul James' High Eyepoint Oculars and the Digicam.

• Peter Evennett's The New Photomicrography [PDF document].

• Micrographia's tutorials on optical designs for microscopy.

• Barry Carter's Afocal Photography.

• The Molecular Expressions Web site.

• Modern Microscopy Web site. See the article on equivalency of digital camera photomicroscopy to Polaroid 4x5 film, "Array Size Needed to Replace Photomicrographs on Film", by Ted Clarke. Also his article, "Fitting a Student Microscope with a Consumer Digital Camera" [PDF document].

• Ching-Kuang Shene's discussion of digital camera lens threads and adapters, particularly in regard to the Nikon Coolpix 4500. Also his page Nikon Coolpix 5700 adapters, which illustrates some potential problems with cameras having extending-turret lenses. Both of these are parts of his digital camera page.

• Giorgio Carboni's Pictures and Movies with the Microscope.

• Edmund Industrial Optics. They offer universal [sic] digital camera microscope couplers, which are essentially large eyepieces that replace your 23mm or 30mm standard microscope eyepiece. Since this approach reimplements the eyepiece optics, the expense runs about $500 to $700 for a complete adapter assembly, which is about 4 times the cost of simpler adapters that use the existing eyepiece. Edmund seems to disclaim any performance for their adapters by stating, "none of the above cameras have been tested, and significant vignetting may occur at lower zoom settings." Also useful for making your own adapters are Edmund's T-mount components.

• Nikon USA paper, Mounting a Coolpix 5000 onto a Microscope [PDF document].

• Raynox camera adapter page. A Japanese manufacuter of step-up/step-down rings and turret-lens adapter tubes. The table provides a reference for the native filter thread size of many cameras.

• The Japanese firm go4dc.com offers attachments to provide filter threads on various digital cameras that don't otherwise have them. Also offers filter thread step-up and step-down rings. Requires Paypal prepayment, then mails you the item from Hong Kong!

• Filter-thread and bayonet-mount adapters are available from online merchants like Adorama and B&H Photo.

• Optical Society of America. Publishes the Handbook of Optics and the Optical Engineer's Desk Reference.

• LightMachinery.com provides free optical calculations and design tools online, including an exact ray trace lens designer.

• William-Jan Markerink's list of camera mounts (Dutch). Stephen Westin (at my alma mater, no less!) has a version in English.

• Navitar's page on Optical characteristics of [C-mount] video lenses.

• R. N. Clark's notes on the resolution, dynamic range, dynamic range, focal length, and f-number of the human eye.

• Cass Sackett's lecture notes [PDF file] on the optics of the human eye.

• Links on optics at www.opticsnotes.com.

• Ian Walker's review of the Zeiss Axiostar universal digital camera adapter. This item appears to replace the eyepiece with an 0.75x negative lens, in addition to the mechanical adaptation of the 30mm eyepiece tube to 52mm filter thread. A telescoping tube with screw lock allows adjustment of the vertex distance.

• Micscape Magazine (UK).

• Lensmate makes filter thread adapters for various Canon Powershot cameras.

• Karen Nakamura on Canon EF mount lenses. She asserts most EF lenses provide 58mm filter threads, with 52mm on some cheaper lenses, 78mm on most professional lenses, and 72mm on some older lenses.

• Alan Wood documents the Olympus OM series of film cameras (1972-2003), for which Olympus produced adapters for fitting to Olympus microscopes, at his Olympus OM System Page.

• Paul van Walree has an excellent Web page on vignetting in the context of ordinary photography. Indeed, while he demurely claims to be "not professionally involved", his pages on optics give general descriptions and photographic examples of optical aberrations, errors, and other effects which outdo the leading textbooks.

• Microscope enthusiast and amateur microscopist P. S. Neely maintains a detailed page on eyepieces as part of his historical collection of AO (American Optical) Spencer Microscope Manuals and Catalogs. He supplies technical specifications on an extensive list of eyepieces from Zeiss, Reichert, Leitz, A O Spencer, Bausch & Lomb, C Baker, CTS, Beck, Wild Heerbrugg, PZO, and Olympus.

• Rolyn Optics provides a 4-page sheet of the most commonly used optical formulas. Also a page with properties of common optical materials.

• Engineering standards for mechanical, optical, and electrical interfacing to microscopes include:
  • DIN standard for 23.2mm and 30mm eyepiece barrels. (I believe these are superseded by the ISO standards below.)
  • ISO 10937:2000, "Optics and optical instruments -- Microscopes -- Diameter of interchangeable eyepieces". Google search for the title. Available at ansi.org.
  • ISO 9345-1:1996, "Optics and optical instruments -- Microscopes -- Imaging distances related to mechanical reference planes -- Part 1: Tube length 160 mm". Google search for the title. Available at ansi.org.
  • ISO 9345-2:2003, "Optics and optical instruments - Microscopes - Imaging distances related to mechanical reference planes - Part 2: Infinity-corrected optical systems". Google search for the title. Available at ansi.org.
  • JIS B 7143:1977, "Engagement between microscope eyepiece and eyepiece sleeves". Google search for the title. Available at ansi.org.
  • ISO 10935:1996, "Optics and optical instruments -- Microscopes -- Interfacing connection type C" (that is, C-mount). Google search for the title. Available at ansi.org.
  • ISO 10939:1998, "Ophthalmic instruments -- Slit-lamp microscopes". Google search for the title. Available at ansi.org.
  • ISO 11882:1997, "Optics and optical instruments -- Microscopes -- Interfacing connection for 35 mm SLR photo cameras (T-thread adaptation)" (that is, T-mount). Google search for the title. Available at ansi.org.
  • ISO 10330:2002, "Photography--Synchronizers, ignition circuits and connectors for cameras and photoflash units -- Electrical characteristics and test methods". Google search for the title. Available at iso.org.

• The "hot shoe" attachment for camera flash accessories is specified by ISO 518.

• Lots of stock step-up and step-down rings, and conversion lens adapter tubes, are to be found for sale at camerafilters.com.