INSTALLING AND OPERATING THE CANON CR6-45NM
NON-MYDRIATIC RETINAL CAMERA
DIGITAL UPGRADE KIT

Richard J Kinch
http://www.truetex.com/


Revised: April, 2011

Description and contents: The digital upgrade kit for the Canon CR6-45NM non-mydriatic retinal camera provides an attachment and electronic interface for a standard digital SLR camera in place of the original Polaroid film attachment. The kit contains the following items:

The upgrade requires the following standard Canon camera equipment which may be obtained from retail camera and electronics retailers:

Any model Canon camera body is compatible with the adapter. Suggested less-expensive models are the Canon Rebel T2i, T3i, or XS. These perform well with the adapter and are all that is needed for retinal photography. If you expect to use the camera for conventional photography off the retinal instrument, consider the mid-range Canon line, such as the Canon 60D or 7D, which provide sturdier construction and a much better viewfinder. High-end models like the Canon 5D Mark II are compatible but will outcrop the image. Any model camera body, including the least expensive, outperforms the theoretical resolution of the Canon retinal instrument, so additional camera resolution will not improve the retinal photography performance.

The Canon lens and extension tube listed above are specifically required for the adapter. Other lenses or extensions will not focus or properly crop the instrument image.

We manufacture this adapter using the original Canon CR-PC Polaroid attachment, which you submit to us for retrofit. We combine new custom parts (which we manufacture in the USA) with certain parts disassembled from the old film attachment to create the new digital adapter assembly. The adapter optics consist entirely of genuine Canon lenses, including some of the original Canon elements plus a new Canon digital EF lens on a standard Canon digital camera. This design ensures a high-quality digital image exceeding the resolution, color, and contrast of the film version. The reliability of the basic Canon retinal instrument is such that you can expect, with proper maintenance, many years of future service from the upgraded unit. Our use of standard digital camera components provides easy service and upgrades with off-the-shelf parts, and a wide range of support in photographic software for image management and enhancement.


Digital camera adapter for Canon CR6-45NM retinal camera, shown with Canon lens and digital camera body
Photo 1. Digital camera adapter for Canon CR6-45NM retinal camera,
shown with Canon lens and digital camera body.

 

The adapter provides mechanical, optical, and electronic features. The adapter assembly, together with the standard camera lens and digital camera body, establish a properly scaled and positioned image for digital photography, with two-way electronic signaling to synchronize the camera shutter with the instrument flash. Mechanically, the adapter provides a Canon EF bayonet receptacle with electrical contacts on the input side, and a 52mm filter thread attachment on the output side. Optically, the adapter includes a portion of the original attachment optics which are supplemented by the digital camera lens. Electronically, the adapter provides electrical connections to the Canon instrument via the bayonet "pogo" pins, which connect to an electronic interface circuit board, which is connected to a camera remote cable and flash sync cable exiting the rear of the adapter.


Canon CR6-45NM retinal camera with digital camera upgrade installed
Photo 2. Canon CR6-45NM retinal camera with digital camera upgrade installed.
 

Installing the adapter:


Canon CR6-45NM retinal camera sample photo from digital camera upgrade
Photo 3. Canon CR6-45NM retinal camera
sample photo from digital camera upgrade.

 
See this image in full resolution (2301x2280) at
http://www.truetex.com/canon_cr6-45nm_v2_sample.jpg
 
See more samples at:
http://www.truetex.com/canon_cr6-45nm_samples/

Parfocal focus calibration:

If you are focusing the Canon instrument with a proper technique on the patient eye properly using the infrared focus indicator, but your digital photos are consistently out of focus, then you should recalibrate the parfocality of the camera and its lens to the retinal camera focus.

Trial-and-error method: It may be simplest to set a parfocal focus calibration by trial-and-error as follows. Start with turning the Canon 28mm lens focus ring for a 0.45m setting on the lens indicator. Carefully focus the instrument on a test subject and take a photograph. Make small modifications to the Canon 28mm lens focus ring setting, and take more test photos, until you determine an optical setting. While this process may be tedious, it may be simpler than disassembling the adapter as in the following procedure.

Disassembled tube method: For a definite focus calibration, use the following disassembly procedure instead of the trial-and-error method.

Additional notes:

Copyright 2009, 2011 Richard J Kinch.