The back door approach to Digital is one of two roads:
1) A "Back Door"...a la the Leica DMR. Put a digital module solely on the back of the camera, with passive shutter-firing detection, and retrofit existing cameras (let's just say, for sanity's sake, R3 and R4 only). Not impossible...could even be hacked from an existing camera's sensor.
Passive detection of the servo/solenoid that fires the "A" cameras' elec. shutter is possible...and, a 2nd (3rd really) shutter in front of the sensor itself is also possible, where you'd set the R camera's shutter to at least two speeds slower and just leave it. Detect shutter fire, and fire shutter on module.
Another way is to have a "wakeup for 1hr" button on the module, and then a laser that is on a frequency that won't bother the sensor detect when the shutter opens. Ultrasonic, put a Hall Effect sensor butted up smooth against the elec shutter solenoid to detect the RF spike when the solenoid fires, both, who knows.
I'm saying it right here, for the technical and business reasons ("Us small guys have to stick together") I'd use the guts of the Sigma DP1...its the right size, has the right sensor, which is alllllready dealing with a fairly wide-angle lens. Yeah, I'd deal and not use it on the 15mm or 12mm or 21mm if I had to....I just want to work with the 40's and 50's...puh-leeeze!
So, you put LCD, chip slot, and buttons allll on the module. Price it accordingly (2200$) and punish those that want digital, and leave me in 475$ land happily.
2) The new epson 6400dpi scanner for 250$.
The #1 approach could be done without any help from CV. I bet I could get it engineered in a "hack" form just by using a de-lensed DP1 with a diopter in front, and later after packaging...skip the diopter (DP1 guts closer to back-frame of R camera. Min focus for the DP1 is 30cm, so, the lens has to come off.
Anyone have 200k$ for the project?
I will be engaging in option #2, for now.
G.
p.s. The Germans willllll make the M8 work right, bet on it. There are ample lenses for it already, so, POOF, that's your R5. IF it is successful, then, Mr. K. will do "the right thing" at the time.
p.p.s. I've laid it all out ("DP1 = R3 back") can someone please build it?