Richard J Kinch

November, 2011.

This document describes how to install and operate the digital camera upgrade kit for the lower port of the Kowa fx-50R series retinal camera, or for the upper port of the Kowa fx-500. Installation differs on the fx-50R model versus the fx-500 model (sometimes designated fx-500S) only in the position of the adapted port, whether lower (below the viewfinder as on the fx-50R) or upper (above the viewfinder, as on the fx-500). The adapters for these various models differ optically, but are essentially identical in their electronic and mechanical interfaces.

Kowa fx-50R with digital camera upgrade
Figure 1. Digital camera with adapter mounted on the lower port of the Kowa fx-50R retinal camera. Rear orientation of the adapter original version shown. Later versions mount only to the left or right orientations due to clearance of the larger diagonal assembly. A stock Canon lens provides superb optical performance for relaying the Kowa image to the Canon digital sensor. The spatial resolution and color depth of the digital system exceeds that of 35mm or Polaroid film, and captures sharper details from the Kowa retinal camera optics. Flash energy is lower and more comfortable for the patient.

Kowa fx-500 with digital camera upgrade
Figure 1. Digital camera with adapter mounted on the upper port of the Kowa fx-500 retinal camera. Left orientation of the adapter shown.

Digital camera adapter for Kowa fx-50R
Figure 2. Adapter shown separately. Kowa bayonet is to the left, with the circular black field stop inside. Canon lens attachment is at the right, ending in a 52mm filter thread fitting. Each end of the current version provides a rotation adjustment using locking thumbscrews. The earlier version (shown) provided a thumbscrew and setscrew to adjust the orientation of the Canon end, and small black setscrews inside the large aluminum ring adjust the orientation of the Kowa end (using a supplied 1.3mm hex key). The front-surface precision diagonal mirror in the middle reverts the retinal image to normal orientation. The optional field lens is not installed in this photo. Current versions of the adapter use a larger, sturdier diagonal mechanism.

Electronic interface cable for Kowa fx-50R digital upgrade
Figure 3. Electronic interface cable. This component consists of a connector block for the Kowa instrument on one end, digital camera connectors in a "Y" arrangment on the other end, and a length of cable in between. DB-25 connectors on the aluminum housing of the connector block insert between the similar connectors on the Kowa instrument base to interpolate the joystick and flash sync signals. Two small connectors on the other end of the cable supply remote actuation to the Canon digital camera shutter from the Kowa joystick, and the flash sync signal from the Canon camera to the Kowa flash trigger. The Canon remote connector shown is a 2.5mm mini jack used with the Canon Digital Rebel models. For the Canon models 40D or 50D, we supply a Canon N3 remote shutter connector instead of the mini jack.

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 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.

Digital upgrade for Kowa fx-50R with Canon 60mm lens
Figure 4. Adapter shown attached to the Canon camera with Canon 60mm lens. Optional field lens is not installed.

Kowa fx-50R retinal camera with right cover removed
Figure 4a. Kowa fx-50R retinal camera with right cover removed. Observe circuit board thus exposed on the fx-50R, and location of connector CNN9 on the circuit board. On the fx-500, see photo below for the relevant connector.

Close-up photo of connector CNN9 on the Kowa fx-50R upper-unit circuit board
Figure 4b. Close-up photo of connector CNN9 on the Kowa fx-50R circuit board. On the fx-50R, modify connector CNN9 by soldering a jumper from pins 1 to 3. On the fx-500, see photo below for the similar modification.

Kowa fx-500 retinal camera with right cover removed
Figure 4c. Kowa fx-500 retinal camera with right cover removed. Observe circuit board thus exposed, and location of connector CNN21 on the circuit board.

Close-up photo of connector CNN21 on the Kowa fx-500 upper-unit circuit board
Figure 4d. Close-up photo of connector CNN21 on the Kowa fx-500 circuit board. On the fx-500, modify connector CNN21 by soldering a jumper from pins 1 to 3.

Modify the Kowa circuit board connector to enable the lower port: This modification permits the lower-port accessory to operate without having to make an electrical connection through the adapter itself.

Attach the adapter to the Canon camera:

Calibrate the focus of the Canon camera to the adapter: Focus calibration is a quick and easy procedure, but it is absolutely critical to the proper performance of the adapter. You must set the digital camera lens to a fixed, manual focus on the adapter's circular field stop, which permits you later to focus the retinal image in the normal way, using only the Kowa focusing knobs.

Attach the digital camera with adapter to the Kowa instrument:

Electronic interface cable for digital upgrade installed on Kowa fx-50R
Figure 5. Electronic interface cable inserted ("interpolated") between original Kowa connectors. This photo shows the lower-right rear corner of the instrument, by the on-off power switch. The length of the new cable is routed along the existing cables and up to the new digital camera.

Electronic interface cable for Kowa fx-50R digital upgrade installed on Canon digital camera
Figure 6. Electronic interface cable attached to the Canon digital camera. This shows a Canon Digital Rebel model XTi camera with hot-shoe adapter on top for the flash sync connection. The flash sync connection runs above the Canon camera viewfinder and into the hot-shoe adapter. Later versions incorporate the hot-shoe connector into the cable, instead of through a separate adapter. The remote shutter connection (2.5mm mini jack for this model) goes inside the rubber flap shown open on the left side of the camera body. The new cable is routed between the Kowa upper unit and the adapter barrel.

Install the electronic interface cable on the Kowa instrument:

Configure the Canon camera for retinal photography:

Configure the Kowa instrument for digital photography:

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 position. 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 exposure brightness and adjust the Kowa flash intensity (that is, the Kowa "EXP MANUAL" dial) to compensate; the digital camera may be more sensitive than the usual film and lower flash intensity is usually indicated.

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

Alternate orientations: By loosening the screws on the adapter, you may turn the fittings on the adapter to set an optional left or right orientation of the assembly, as shown in Figure 7 below, instead of the rear orientation shown in Figure 1 at the start of this document. Later versions of the adapter are of a heavier construction which only permits the right or left orientation. The right and left orientations allow the operator to be closer to the Kowa viewfinder and the patient. You must adjust the cable slack to allow for more or less movement in the given orientation.

On the fx-500, the upper port attachment further allows you to optionally orient the camera to the front of the instrument with the digital camera inverted, instead of to the side. While it is also possible to orient the digital camera upright and to the rear, above the viewfinder eyepiece, the digital camera body will likely interfere with the observer's head prevent approaching the viewfinder.

Adjustment for odd orientations are possible, but the image will be rotated in the photograph and no longer upright. For example, you may position the adapter for the right orientation, but rotate the camera to be horizontal (instead of on its right side as shown in Figure 7). This will rotate the image in the camera by 90 degrees into a portrait orientation. It may be more convenient to have the camera controls upright with the photos rotated rather than vice versa.

Optional orientations of the digital adapter on the Kowa fx-50R
Figure 7. Optional orientations of the adapter on the Kowa instrument. The adapter and camera may be adjusted for the left or right orientations shown here, instead of facing the operator. The digital camera must orient as shown, instead of being upright, to keep the photographic image upright instead of rotated, as a consequence of the rotated mirroring path.

Internal Kowa circuit board modification required for the lower-port adapter: The lower-port adapter does not use the "pogo stick" terminals on the bayonet connection, and thus requires the modification to an circuit board connector CNN9 to "cheat" the camera-present signal. We will have installed this modification on your instrument if you sent it physically to us for refurbishment and upgrade. If you are performing a do-it-yourself field installation of the upgrade, follow the instructions above to implement this modification. The modification is reversible and backwards-compatible with lower-port attachments such as the original Polaroid camera which Kowa supplied.

Using the optional field lens: We have provided in the adapter kit a single-element glass lens which you may install in the Kowa end of the adapter. This will allow you to use smaller aperture settings in the Canon 60mm lens than the widest F2.8 setting, should you need to reduce exposures below the lowest flash energy setting of the Kowa instrument and slowest ISO speed setting of the digital camera. Without this lens in place, smaller apertures in the Canon lens (for example, F4.0 or F8.0) will cause vignetting in the image (the edges of the field of view will be gradually blacked out). With the optional field lens in place, any smaller aperture setting down to the smallest provided by the Canon 60mm lens (namely, F32) may be used without vignetting. This less light-sensitive adjustment of the camera is not normally needed, since the Kowa EXP MANUAL control adjusts the flash energy to very low levels, but the option is available. Most applications therefore do not require the optional field lens, and you should thus not normally install it, since it inevitably gathers dust that, until cleaned off, tends to cause distracting specks on every photograph.

Optional field lens for Kowa fx-50R digital upgrade adapter
Figure 8. Optional field lens which you may install in the Kowa end of the adapter. The black circular opening behind the lens is the field stop. The black ring with two holes is the retaining ring. Normally this lens is not used, and the adapter tube is open on this end through the retaining ring and field stop.

To install or remove the optional field lens:

Figure 9 below shows a later design for the adapter tube which uses a heavier elbow component resulting in a studier assembly.

Later design of the Kowa fx-50R digital camera adapter
Figure 9. Later design of the adapter tube with heavier elbow component.

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.

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 Canon lens aperture and the flash energy on the Kowa 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.

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.

Copyright 2008, 2009, 2010, 2011 Richard J Kinch