for the
TRC-50EX and TRC-50IX
TRC-50X and TRC-50IA
TRC-50VT and TRC-50V
TRC-50F and TRC-50FT

Richard J Kinch
January, 2010

This document describes how to install and operate the digital camera upgrade kits for Topcon TRC-50 series and TRC-W series retinal cameras. The various adapter models are similar but support variations in the Topcon models according to the following table:

Adapter Kit
Upper Port
Digital Cameras
EF-TRC-50VT M64x1.0
threaded ring
15-pin D-sub Joystick interpolation
with asynchronous flash jumper plug
All Canon digital SLRs
Nikon digital SLRs with 10-pin remote
EF-TRC-50F None; rear-port
bayonet only
None Joystick and synchronous flash
internal take-off cable
or pogo connector
Canon or Nikon full-frame digital SLRs
  (Canon 5D or 5D Mark II)
EF-TRC-50X-50IA M64x1.5
threaded ring
15-pin D-sub Synchronous connection to
upper-port connector;
Optional internal retrofit with upper-port
mirror-synchronization switch
With mirror-synchronization switch upgrade:
  All Canon digital SLRs
  Nikon digital SLRs with 10-pin remote
Without switch upgrade:
  Canon 40D or 50D only
9-pin D-sub Synchronous connection to
base connector
All Canon digital SLRs
Nikon digital SLRs with 10-pin remote
EF-TRC-W M62x0.75
threaded ring
Manual shutter
release cable
Manual mirror actuation cable with
adjunct digital shutter control
and synchronous flash
All Canon digital SLRs
Nikon digital SLRs with 10-pin remote
Note 1: Specify F-mount SLR bayonet when ordering for use with supported Nikon digital SLRs.
Note 2: Rear-port adapters for Topcon TRC-F/FE/JE retinal cameras also available.

The following instructions apply generally to all these various adapters, although we will illustrate with the Topcon TRC-50EX model, unless otherwise indicated.

Figure 1. Digital camera adapter assembly for Topcon TRC-50EX. Shown with typical digital SLR camera body.
This model attaches via the bayonet fitting on the TRC-50EX upper port. Other models attach with a screw ring captured on the adapter tube.

Figure 2. Adapter mounted on Topcon TRC-50EX.
This Topcon model has a fixed viewfinder. Older Topcon models incorporated a viewfinder into the 35mm film camera back attached to the instrument's rear port; on such models we will retain the film camera for viewfinding, while photographs will be taken on the upper-port digital camera.

Figure 3. Cross-sectional view of adapter internal structure.
The adapter supplies three different aspects of adaptation: mechanical, optical, and electronic. The mechanical tube makes the physical connection to the instrument, and holds the camera and optical elements in the proper orientation and aperture. The optical elements relay and resize the instrument image onto the digital camera's image sensor. The electronic interface cable forwards the shutter triggering signal from the instrument to the camera, and in turn the flash synchronization signal from the camera back to the instrument.

Installation instructions:

Operating instructions:

Photo 1. Adapter and camera mounted on Topcon TRC-50EX.

Photo 2. Close-up of TRC-50EX adapter with Canon 400D digital SLR camera.

Photo 3. TRC-50VT console settings for digital photography with the upper-port adapter.
Observe that the "UPPER" indicator is lit, showing that the upper port is selected for photography. An earlier version of this console uses green push-buttons instead of membrane switches, and the button is labeled "35mm UPPER".

Photo 4. TRC-50X console settings for digital photography with the upper-port adapter.
Observe that the rotary switch is on "35mm", and the "UPPER" indicator is lit, showing that the upper port is properly selected for photography.

Further Notes

Adjusting the adapter rotation: If the edges of the Topcon field are not parallel to the digital image rectangle, loosen the small setscrews in the EF lens T-mount adapter and rotate the camera slightly to obtain rotational alignment.

Adjusting the crop ratio: The crop ratio of the image refers to how the oval Topcon image scales into the digital frame. The edges of the Topcon image field should normally be scaled to fall just inside the full digital frame; this crop factor cannot be adjusted except by shimming the relay lens or changing the tube length.

Mirroring in software: Since the light path to the upper port involves an odd number of mirrors, the image recorded by the digital camera is mirrored from normal. Since digital images are easily un-mirrored in post-processing, we have chosen not to build a physical mirror into the adapter.

Calibrating for parfocality with the adapter focus: You can adjust the focus of the adapter on the field mask by loosening the nylon setscrews on the adapter tube and telescoping the relay lens by trial-and-error in and out of the outer tube. Use the Canon viewfinder (after carefully calibrating it for your diopter setting) while holding the adapter up to a diffuse light source to examine the field edges. The finest focus calibration is obtained by checking the focus of the field mask with digital images, selecting the highest magnification in the Topcon instrument (that is, the narrowest retinal field angle). Note that the best focus available on a 10 megapixel camera image will not resolve down to anything close to single pixels.

The finest focus adjustments cannot be seen directly in the viewfinder, and require observing Moire patterns with a 40 lp/mm Ronchi ruling test target such as Edmund Optics part number 38-260, or the variable frequency versions 38-582 or 43-488 (this last item being the one we use here in our lab). Without such a test target, the fine focus point can be laboriously found by making slight adjustments and viewing zoomed-in test exposures.

If the field mask is in focus in the digital images, but the subject itself appears out of focus despite your best viewfinder focusing efforts, then check the parfocality. Parfocality can be difficult to achieve because it includes every factor in the viewfinder, including: the viewfinder diopter setting, the calibration of the viewfinder, the observer's refraction Rx, and the observers (possibly unintentional) accommodation. In general, each operator will require a specific diopter setting on the viewfinder to null out the sum of all these focusing factors and establish parfocality of the camera with the viewfinder image. The best way to determine this viewfinder diopter setting is to first verify and/or calibrate the field mask focus as above, and second to take a series of digital photos of a fixed test subject with a range of viewfinder diopter settings, yielding a best-focus setting in whole diopters. Given a whole-diopter setting for best-focus, a second series of photos may refine that setting to a half-diopter adjustment on the viewfinder eyepiece. This ultimate best-focus setting may or may not correspond to the eyepiece crosshairs being viewed in focus, because the calibration of the eyepiece may itself be off.

Adjusting exposure time (except TRC-50VT models): The exposure time setting in the Canon camera is chosen to keep the shutter open during the latency initiated by the camera's signal to the Topcon instrument to fire the flash. The 1/6, 1/10, or 1/30 SEC recommended above is not necessarily the shortest exposure time possible, so you may wish to experiment with shortening the exposure time while observing that the exposure captures the flash illumination. The shortest exposure time is generally preferred, as this will minimize the light integrated from the steady illumination lamp, improving the sharpness of the exposure and avoiding any blurring from patient motion. On the TRC-50VT adapter with asynchronous flash jumper plug and 1/6 SEC exposure time, the flash lag is already minimal with the upper-port mirror-flip, and shorter exposure times will miss the flash entirely.

Adjusting adapter speed via relay lens aperture: The relay lens in the adapter incorporates an adjustable aperture which may be used to stop down the light path from the instrument. This will decrease the sensitivity if the digital camera proves too sensitive to the lowest energy setting of the Topcon flash illumination. Smaller apertures will also improve the depth of focus on the adapter's relay imaging of the instrument image (although not the depth of focus on the subject).

To access the aperture adjustment:

Stopping down the aperture will tend to improve the focus of the adapter on the Topcon image field, at the expense of brightness. It will not affect the depth of field or focus of the instrument with respect to the subject retina.

Adjusting the ISO speed of the digital camera: The Canon digital cameras offer a range of ISO speeds, from 64 or 100 up to 800 or 1600. This provides you another variable affecting the exposure of the digital photograph, along with your ability to vary the adapter aperture (explained above) and the flash energy on the Topcon instrument. Higher speeds of ISO 200 or 400 will enhance the sensitivity of the camera while not introducing much noise. Speeds of 800 or more will typically introduce a degree of speckled noise into the pixels of the photograph, especially considering that the retinal image is by nature of very low contrast. Use the histogram feature of the digital camera to analyze your retinal images for proper exposure level and to observe the degree of contrast. The position of the hump in the histogram indicates the exposure level, which should be around the middle of the range, and the width of the hump indicates the contrast of the retinal image elements.

Cleaning the adapter optics: Dust on the field lens of the adapter, being close to a focal plane of the instrument, will tend to show up as a repeating artifact on photos. For this reason it is important to keep the field lens scrupulously cleaned. The outside of the field lens can be cleaned in the usual manner with lint-free non-abrasive tissue (such as Kimwipes) slightly moistened with glass cleaner, and brushed and puffed lightly with a lens cleaner such as is sold in photo shops. The Topcon lenses on the rotary turret just inside the upper port (on some Topcon models), and the Topcon mirrors, are likewise very sensitive to dust and should be carefully cleaned. If the inside surface of the adapter's field lens should need cleaning, unscrew the upper-port fitting from the adapter tube to access the other side of the lens. For advanced field lens cleaning, the retaining ring holding the field lens element in the upper-port fitting may be unscrewed by inserting a small jeweler's screwdriver into the spanner wrench holes. Remove this element, clean it, and return it carefully into the upper-port fitting and secure the retaining ring. Note that the field mask is very thin and exposed metal, and will be easily damaged if mishandled.

We do not recommend removing dust with a canned-air duster. These may spit bits of liquid refrigerant which will "frost bite" the lens coating and cause a permanent spot. If you use a canned duster, hold the can down on a table top to steady it, and move the item being cleaned in front of the nozzle, instead of moving the can and possibly swishing the liquid up to the dispenser valve.

Topcon TRC-50EX/IX ONLY: Power the camera down when not in use: You should manually turn off the power switch to the Canon camera before powering down the TRC-50EX/IX, because these Topcon models lock the shutter signal closed when its power is off. This will cause a spurious exposure to be recorded in the camera, but more significantly it will drain the Canon camera battery if the camera is left on. If the TRC-50EX/IX is left powered-on but idle, with the Canon camera also left on, the Canon camera will auto-power-down to conserve its battery, and reawaken when an exposure command later comes from the TRC-50EX/IX.

Using an AC adapter on the Canon camera: To avoid having to worry about having a charged Canon camera battery, you may wish to purchase the Canon optional item that powers the camera from an AC adapter.

Lowering resolution on the camera: Since the highest resolution images of the camera are finer than the optical resolution of the instrument, you may wish to set the camera to record lower-resolution images.

Tethering software: If you want to have live previewing and capture of photos on a computer while shooting with the Canon camera, consider using "tethering" software. This type of application uses a "tether" from the camera to the computer via a USB cable. A simple version is included with the Canon camera software support disc. DSLR Remote Pro ( is one popular aftermarket package sold for this application. Contact us for availability of ophthalmological tethering software.

Alternate Canon camera models: Full-frame Canon digital SLR cameras (such as the model 5D or 5D Mark II) can be used with the small-format adapters, however the field will be under-cropped by a 1.6X factor. A slightly longer outer tube must be substituted to obtain a proper full-field crop. Contact us for availability.

Alternate makes of digital cameras: Other makes of digital SLR cameras can be used with this adapter, if they provide a similar format size and shutter/flash synchronization. The adapter incorporates T-mount mechanics to make interchange inexpensive. Contact us for compabitility information on specific alternate make and model cameras. Certain Topcon models require a very short shutter lag, and many less expensive digital SLRs are not compatible because of their relatively long shutter lag characteristics.

For this reason of critical shutter-lag timing, point-and-shoot cameras are completely unsuitable, even if they were to be optically adapted.

Limited warranty: We manufacture this adapter to high standards, and guarantee the performance will be in accord with the specifications. Please contact me via email ( should you have any difficulties we can correct.

Copyright 2007, 2008, 2009, 2010 Richard J Kinch.