Richard J Kinch     April, 2012

Kowa fx-50C retinal camera with digital upgrade installed
Figure 1. Kowa fx-50C retinal camera with digital upgrade installed. [HI-RES]
This shows the normal orientation of camera below and to the right of the viewfinder.
This allows the operator to access the Kowa viewfinder eyepiece with either eye,
and to access the digital camera display and controls.

Identify the upgrade kit contents:

Other components you must obtain separately:

The adapter kit works by design with ordinary, standard Canon retail camera bodies and lenses, and with the constantly improving standard computer software supporting digital photography. No special version or modifications of camera hardware or software are required. New Canon camera models in the future should also be compatible, as should advances in Canon and third-party computer software support. You may process the standard RAW or JPEG images using industry standard software such as Adobe Photoshop or Corel PhotoPaint.

Optional components you may wish to obtain separately:

Familiarize yourself with the digital camera and lens: If the digital SLR camera is new to you, study at least the following features which will be used for retinal photography: On/off switch, mode switch "M" setting for manual operation, setting manual exposure time, attaching and removing lenses, remote shutter release connector, viewing photos on the camera, transferring photos to a computer.

Also read the instruction manual for the Canon 60mm lens to learn about the following features of the lens: filter mounting thread, focusing ring, focus mode switch, and distance scale. You must understand these features to apply the manual focus calibration procedure below, which is mandatory for proper operation of the adapter.


Modify the Kowa circuit board connections to enable the rear camera port:

This modification permits the rear port to operate without having to make an electrical connection through the adapter itself.

Attach the adapter to the Canon camera:

Calibrate the Canon digital camera focus to the Kowa instrument focus

Proper focus calibration is critical to good pictures
The clarity of all subsequent digital retinal photos depend on a proper manual lens focus calibration. Once the focus calibration is properly set and locked, you should not have to perform the calibration again. If you find your retinal photos are consistently out of focus, yet you are sure your technique with the Kowa instrument and its focus are correct, check the Canon lens focus calibration and recalibrate if needed. You can reinsert the focal plane gage pin for this purpose, or you can use a trial and error technique starting with the 0.25 meter setting on the Canon 60mm lens scale.

Choose and set an initial orientation for the camera and adapter:

Attach the digital camera with adapter to the Kowa instrument:

Install the electronic interface cables on the Kowa instrument:

Configure the Canon camera for retinal photography:

Configure the Kowa instrument for digital photography:

The Kowa fx-50C provides a single fixed flash energy which is not adjustable. Accordingly there are no adjustments available on the instrument to correct overexposure or underexposure. If digital photos are underexposed, you may increase the digital camera sensitivity by increasing the ISO speed setting, such as to ISO 200 or ISO 400. If digital photos are overexposed, you may use a smaller lens aperture. That is, apply a smaller lens aperture setting (higher manual f/number) to stop some light and decrease the overexposure, such as F4.0 or F6.3 instead of F2.8. Note that at some point smaller aperture settings will vignette the edges of the photo. To correct overexposure while maintaining the non-vignetting F2.8 aperture, stack an ND2 or ND4 neutral-density filter (52mm size, available inexpensively from camera dealers or online) between the digital adapter and the Canon lens. Since the exposure is determined by the flash energy reaching the digital camera, changing the exposure time from 1/4 SEC will not affect the exposure, although shorter exposure times will cause the digital camera to miss the flash entirely.

Adjust the instrument for a fixed test subject: Tape a business card or other flat, high-contrast, detailed subject to the patient headrest to serve as a fixed test target. A long strip of clear packing tape stuck across the headrest poles at the canthus marks will serve well. Stick the tape to the operator's side of the poles, and stick the card slightly to one side, roughly offset to where a patient eye would be positioned. Frame and focus a view of this target using the Kowa viewfinder in the normal fashion, perhaps pulling away from the subject and using the "+" refraction compensation, as for anterior segment views.

Take test subject exposures: Focus and align on the test subject using the instrument viewfinder in the usual way. Press the joystick button to trigger an exposure. At the moment of exposure, listen for the Canon camera mirror flip and shutter mechanisms operating, along with the Kowa mirror mechanism flipping. Observe the light of the retinal camera flash on the subject. Immediately after the exposure, the Canon camera should momentarily display a view of the image on the rear display.

Review test subject exposures: If you are using a tethered PC to capture photos, refer to the tethering software user manual for image review. If you are using the stand-alone camera to shoot onto the camera's memory card (with no tethered PC), use the Canon menu buttons to manually review exposures on the camera display. You may lengthen the automatic review time with the "Review time" menu setting on the digital camera. Zoom in when reviewing images to verify that image is sharply in focus when the viewfinder was also in focus. Note that the full resolution of the digital camera is much finer than the instrument resolution, so the highest-resolution images will not appear in focus when zoomed in completely.

Take live subject exposures: It is most convenient to obtain a cooperative, well-dilated colleague or patient for your first live retinal digital image tests. Collimate and focus on the retina in the usual way with the viewfinder, using the joystick button to take exposures. Check the images for proper exposure brightness; the digital camera may be more sensitive than the usual film, so exposure adjustments from your usual technique may be necessary.

Establish your practice routine: After completing the above, you will have a powerful digital facility for retinal photography. You must now handle digital data where you used to handle 35mm film slides or Polaroid prints. It most regards the digital methods are quicker, easier, and cheaper than film, but do require an initial investment in careful design and training. Your digital system is based on standard digital cameras, and so is compatible with ordinary software for capturing, post-processing, and cataloging digital photographs. Your upgraded digital retinal camera should, with occasional maintenance, provide decades of reliable service.

Further Notes

The instrument is effectively a manual lens: The Kowa instrument in effect becomes a manual lens for the digital camera. The Canon lens is set at a fixed focus and acts only as a relay lens.

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. This will decrease storage space and improve tethered transfer times.

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. Tethering to a computer with a large display is the best way to instantly review your photos for proper focus and exposure while you still have a chance to retake a missed shot. The small display on the camera does not adequately reveal the quality of the image focus.

Using the digital camera off the instrument: You may remove the Canon camera and/or lens from the Kowa adapter to use them for ordinary photography, but you must repeat the manual focus calibration and tape-locking if you remove the tape from the lens and lose the Kowa focus calibration. To avoid this problem, dedicate the Canon 60mm lens to the Kowa instrument, remove only the Canon digital SLR body when using the camera off the Kowa instrument, and obtain separate lens(s) for such use.

Digital camera adapter for the Kowa fx-50C retinal camera
Figure 2. Digital camera adapter for the Kowa fx-50C retinal camera.
The bayonet fitting attaches to the Kowa instrument.
Threaded end screws into Canon digital camera lens.

Jumper plug for Kowa fx-50C circuit board
Figure 3. Jumper plug for circuit board.
Installing this plug into the Kowa circuit board allows the digital camera to operate
without any connections through the bayonet fitting itself.
This photo shows an enlarged view; the actual item is only about 1/2 inch long.

Locations of right-cover screws on the Kowa fx-50C
Figure 4. Locations of right-cover screws.
Remove the indicated six screws and the focusing knob to remove the right cover from the instrument.

Kowa fx-50C upper unit with right cover removed
Figure 5. Upper unit with right cover removed.
This allows access to the upper unit circuit board.
Disconnect the original wiring and install the jumper plug at the location indicated (connector JM7).

Close-up of Kowa fx-50C jumper plug installed
Figure 6. Close-up of jumper plug installed.
Use cable ties to secure the loose original plug and wiring as shown.

Digital camera adapter for the Kowa fx-50C retinal camera
Figure 7. Digital camera adapter.
This view shows the thumbscrews used to adjust and lock various orientations of the adapter.

Lens fitting for the Kowa fx-50C digital camera adapter
Figure 8. Adapter fitting to the digital camera lens.
The black threaded portion screws into the filter threads of the Canon digital camera lens.
The silver tube slides into the adapter diagonal receptacle and is locked into place with
the thumbscrew.

Kowa fx-50C bayonet fitting with focal plane gage pin installed
Figure 9. Bayonet fitting with focal plane gage pin installed.
The brass pin with hexagonal head screws into the inside face of the bayonet fitting.
This pin is installed into the adapter when shipped.
View the mirrored image of the face of this pin in the digital camera viewfinder, and
adjust the digital camera lens manual focus to calibrate the camera focus to equal the Kowa instrument focus.
Remove the gage pin and replace with a normal screw after performing the focus calibration procedure.

Detailed view of the focal plane gage pin for the Kowa fx-50C
Figure 10. Detailed view of the focal plane gage pin.
Focus the digital camera manually to the
small face of the probe tip, which is the calibration target.

Digital camera views of the Kowa fx-50C focal plane gage pin
Figure 11. Digital camera views of the focal plane gage pin.
First photo shows the face of the gage pin properly in focus near the right side of the image.
Only the face of the pin as seen in the mirror will be in focus, not the direct view of the shaft of the pin.
Second photo shows an incorrect focus on the pin shaft instead of the correct focus on the pin face.

Setting the Canon 60mm lens focus to 0.25 meters
Figure 11A. Setting the Canon 60mm lens focus to 0.25 meters.
Turn the manual focus ring so that the focal distance scale reads as shown.
The tick mark is pointing at the zero in the 0.26 indication.

Digital camera electronic interface cables for the Kowa fx-50C
Figure 12. Digital camera electronic interface cables (connectors to Kowa instrument).
First cable on left is the plug which inserts into the base of the Kowa instrument.
Second cable on right is the receptacle which mates to the separated plug on the cable from the joystick carriage on the Kowa instrument.

Digital camera hot shoe plug Canon digital camera remote shutter E3 connector
Figure 12A. Digital camera electronic interface cables (connectors to Canon digital camera).
Connector on left is the hot shoe plug which inserts into the flash hot shoe receptacle on top of the digital camera.
Connector on right is the remote shutter plug which inserts into the remote shutter receptacle on the side of the digital camera.

Original joystick connection on Kowa fx-50C before digital upgrade
Figure 13. Original joystick connection before digital upgrade.
The plug and receptacle are fastened with a threaded lock ring.
Unscrew the lock ring and pull apart the connectors.

Separated joystick connectors on the Kowa fx-50C
Figure 14. Separated joystick connectors.
This shows the original receptacle on the base of the unit, and the original plug
on the end of the cable from the Kowa joystick carriage.

Digitally upgraded joystick connections on the Kowa fx-50C
Figure 15. Digitally upgraded joystick connections.
Connect the new cables to the original plug and receptacle as shown, tightening the
threaded lock rings to secure the connections.
Dress and cable-tie the wiring as shown in Figure 1 above.

Kowa fx-50C retinal camera with digital upgrade installed in upper alternate orientation
Figure 16. Digital upgrade installed in upper alternate orientation.
This shows the alternate orientation of camera, to the left and above the viewfinder.
This allows access to the digital camera display and controls, but only the operator's
left eye can reach the Kowa viewfinder eyepiece.

Kowa fx-50C retinal camera with digital upgrade installed in lower alternate orientation
Figure 16A. Digital upgrade installed in lower alternate orientation. [HI-RES]
This shows the alternate orientation of camera, to the left and below the viewfinder.
The operator may look into the Kowa viewfinder eyepiece with either eye.
Access to the digital camera display and controls is limited.

Another orientation possible for the Kowa fx-50C digital camera adapter
Figure 17. Another orientation possible for the adapter.
This orientation is convenient for reviewing settings and photos on the camera, but
inconvenient for the operator to view into the Kowa viewfinder eyepiece.
Torque on the adapter fittings also requires that the adapter be modified for additional
screws to strengthen the diagonal adjustments.

Copyright 2008, 2009, 2010, 2011, 2012 Richard J Kinch