Requirements of older cameras

(This page will be updated periodically to reflect the state of the art in the general development of digital conversion kits, without regard for specific manufacturers and models.)

Welcome to a general discussion of the various design considerations, limitations, functionality and features of a digitally-converted fundus camera.

Below, for the curious, you will find information we discovered as we've researched and developed our line of kits, as well as information gleaned from reliable sources (such as the manufacturers themselves) that may answer some of the vexing questions facing the practitioner with an older film-based fundus camera.

As always, please feel free to send an email, or make use of our comment/contact page, if you have an issue you'd like for us to address here.

In no particular order:

Mydriatic or Non-mydriatic, that is the question...

The main consideration when dealing with a non-myd camera is that a non-myd photo is really only non-myd (at least on many previous generation models) right up until the nanosecond when the visible flash triggers - then it's back to the 5-6 minute wait for the pupil to fully redilate / recover. That entails a camera setup that relies on non-visible (in the case of almost all older fundus units, IR) light and a video system sensitive enough to it to allow focussing on a CRT using only this IR source. In all of the Topcons, for example, prior to the NW6 series, this was accomplished with the "chimney" light path design that allowed for simutaneous overlap of the image from the retina and a focussing target derived, in part, from that same retinal image.

In all previous incarnations of the Non-Myds, this takes the form of a separate video camera imbedded in the housing of the retinal camera, and an optical adapter that is specifically designed to attach to the viewfinder of the 35mm or polaroid back to allow both images (from the primary and secondary cameras) to fall on more-or-less the center of the CRT screen.

SO, in order to FULLY convert one of these non-myd cameras to a digital non-myd, you must re-create these same circumstances. This means building a custom relay lens adapter that would beam-split the image entering the digital camera back, and coincide it with the same image, as modified by the Topcon/Canon/Nikon/Kowa internal video camera, and then  send these coincident images to the CRT target screen. (Hang in there, I'm almost done!)

As a result of the added R & D and expense of building such an adapter, you'd essentially add substantially to the cost of the basic kit (the last time I seriously looked at doing this, I researched the available digital conversions, and they were all in the low to mid 5-figure range!). The alternative, using the existing Polaroid attachment as a starting point, works for some, but not all such fundus cameras, and is still a pricey proposition.

Remember, this system, once in place, still retains the characteristics of analog film capture - ie., once the flash triggers, it's back to the waiting game for the next shot. Remember, also, that over 80% of practitioners using a non-myd camera actually dilate the patient anyway (makes for a much more pleasant patient experience). (This statistic was calculated within a study commissioned for Topcon some years ago.)

Fundamentally, how does it do that?

One of the issues all digital conversions must resolve in order to work reliably is to first ensure a solid connection of the digital camera back to the fundus unit. Since many of these units have already received some moderate to heavy use in the field, the ideal adapter would precisely match the specific bayonet mount used by that paricular unit, including any dings or bent alignment pins that are extant. Other digital conversion systems solve this dilemma by requiring the actual fundus unit be shipped to the supplier, who then modifies the fundus unit to fit the adapter. We weren't happy with the idea of shipping an expensive optical instrument via freight twice in order to achieve a good alignment fit. 

As a result, we decided that we wouldn't try to lower the river when we could simply raise the bridge. What we do, instead, is to work with the existing 35mm or Polaroid back. By removing the ring bayonet from the existing back and incorporating it into the new digital ring adapter, we're able to construct a well-fitting adapter ring assembly for your camera, and the only item that must be shipped is the old camera back. This "donor" back is then returned to you, along with the remainder of the kit (a trigger box with built-in cable harness, and a flash-sync cable with built-in current-isolation circuitry). Upon arrival, you simply mount the camera to the adapter ring, and the camera-with-adapter to the fundus unit. And that's essentially all you need.

There are, of course, some very cool options offered to enhance your photo-capture experience; they are really just that -- options. The "secret" to our success lies in the application of the fundamentals above.

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