Richard J Kinch, Ph.D.
December, 2014

This document describes how to install and operate the digital camera adapter for the Canon CR4-45NM. This adapter allows you to use a standard Canon digital camera to take high-quality digital retinal photos and to process them with standard computer hardware and software.

We produce this adapter using your old Polaroid camera attachment (CR4-PC or CR4-PC DUAL, see Figure 1 below). You must send this attachment to us for refurbishment and retrofitting for digital camera use. The retrofit includes mechanical, optical, and electronic components. We will also clean, lubricate, align, recushion, and make minor repairs to your submitted attachment as needed.


Depending on which digital camera type you will be using, your adapter kit provides the following electronic adapters:


The following digital camera components are required to complete the installation, and not included with the digital adapter. Obtain them separately from a retail camera dealer or electronics retailer:

Upgraded camera models: More expensive Canon models include the mid-range Canon 40D, 50D, 60D, 70D, 7D, and 7D Mark II. High-end full-frame models such as the Canon 5D Mark II will work but with an 0.6X crop factor. Photo quality is excellent with any current model, including the less-expensive Rebel types above, so choose a more expensive model only if you want to use the digital camera for conventional photography off the retinal camera instrument.

Familiarize yourself with the digital camera: If the digital SLR camera is new to you, be sure the learn about the following features which will be used for retinal photography: On/off switch, mode switch for manual settings, setting manual exposure time, setting manual lens aperture, attaching and removing lenses, remote shutter release connector, flash bracket and hot shoe, viewing photos on the camera, transferring photos to a computer. If you will be tethering the camera to a computer for live display of photos, you may wish to connect the camera and computer, and shoot some ordinary photos in tethered mode, to familiarize yourself with the procedure.

No tools are required to assemble or install the adapter and digital camera.

Optional components you may wish to obtain separately:


Figure 1. The original Polaroid attachment before upgrade.

Figure 2. Canon camera, extender, and lens, with black adapter tube.
This shows the Canon model 40D digital SLR body.
(Note: does not show optional ND8 filter.)

Figure 3. Camera and lens assembled with black adapter tube.

Figure 4. Retrofitted Canon attachment. Old Polaroid film back has been removed by us and replaced with a digital attachment fitting and electronic interface circuitry.

Figure 5. Retrofitted attachment assembled with Canon digital SLR lens.

Figure 6. Attachment with digital camera on the instrument.

Figure 7. Close up of the complete digital attachment.
Canon 40D digital SLR shown, with flash sync connection on left side of camera.
Current adapters provide a hot shoe connector which attaches to the flash bracket on top of the camera.

Figure 8. Sample non-mydriatic retinal photo with digital retrofit and Canon DSLR.
See also in full-resolution.

Viewfinding with the digital camera live view: If your Canon digital SLR models provides a live view capability (such as the Canon Rebel XSi or T1i models), this can be used for viewfinding on the instrument with the infrared filter out. (Canon digital camera image sensors all contain an infrared blocking filter which prevents the camera from seeing the infrared viewfinding illumination.) Since using a bright and visible exam light for viewfinding defeats the non-mydriatic viewfinding principle of the instrument, digital live viewing will require that patient eyes be dilated to an adequate pupil diameter for successful photography.

All that is necessary in the adapter is to raise the mirror in the attachment and to fix it in the raised position using a bit of tape. Then set the digital camera to live view mode as explained in the camera's user manual. The digital camera can display the live view on the camera's display, or you can connect the camera via a USB cable to and computer and software for live PC preview ("tethering") at higher resolution and larger size.