Full frame sensor question

garry71

garry71

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Garry
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Are there any practical reasons why a 35mm rangefinder/compact sized camera can't be made with a full frame sensor?
I'm assuming that the sensor would be in the same plane as the film would have been, and that the lens would be similar to what used to be on a 35mm film camera.
Or am I barking up the wrong tree technically?
 
Yes it can be done, as Voyager said. The M9 does.

But there is also a practical difficulty. Image sensors require light to hit them reasonably straight-on. For a Full-Frame SLR this isn't too big a problem because the sensor is ~45mm behind (44mm for canon EOS, 46.5mm for Nikon F, etc) the lens flange - that distance means that even the extreme corners of the sensor aren't at too severe an angle of incidence.

However, on a rangefinder the register is much smaller - 27.95mm for Leica M bayonet. That means that the corners of the sensor will receive light at a more acute angle. This effect can be mitigated somewhat by offset microlenses, but it still becomes a problem. Leica have implemented an auto-correction of vignetting (much like Canon DPP can do for the lenses) for the M9.

Note that this vignetting is in addition to the "natural" vignetting of the lens.

So, in summary, it can be done but it has technical challenges to overcome.
 
I wasn't aware of the M9, cheers.
I've seen the proposed Fujifilm X1000, which has an aps C sized sensor, which is why I wondered about full frame.
It'd be nice to have a compact with viewfinder, and a bit of weight instead of waving some lightweight plastic around at arms length.
The leica is well over budget, but the X1000 could be tempting when it arrives.
 
I-S said:
Yes it can be done, as Voyager said. The M9 does.

But there is also a practical difficulty. Image sensors require light to hit them reasonably straight-on. For a Full-Frame SLR this isn't too big a problem because the sensor is ~45mm behind (44mm for canon EOS, 46.5mm for Nikon F, etc) the lens flange - that distance means that even the extreme corners of the sensor aren't at too severe an angle of incidence.

However, on a rangefinder the register is much smaller - 27.95mm for Leica M bayonet. That means that the corners of the sensor will receive light at a more acute angle. This effect can be mitigated somewhat by offset microlenses, but it still becomes a problem. Leica have implemented an auto-correction of vignetting (much like Canon DPP can do for the lenses) for the M9.

Note that this vignetting is in addition to the "natural" vignetting of the lens.

So, in summary, it can be done but it has technical challenges to overcome.
Click to expand...

I thought full frame and film would be a straight swap so to speak, I didn't realise there was more to it than that.
Must be why digital backs for 35mm SLRs didn't make it to the market.
 
Garry, that's one reason but there are others. For example, the distance between the velvet slot where the film exits the canister and the edge of the "gate" (not sure of the correct term in stills cameras) is different in each model, so the sensor film doohickey would either need to be specific to each make and model or be adjustable.

IIRC, the M9 and other FF bodies use a combination of angled microlenses and software correction to keep the corners evenly illuminated.
 
Digital "backs" for film SLRs didn't make it for rather more mundane reasons. Not many cameras were offering interchangable backs, and without removing the back you couldn't have a review/settings/live view screen. Film cameras weren't designed with power sources for digital in mind so would have required additional, separate battery packs, etc. The integrated DSLR was a far better technical solution.

Again, Leica DID do the digital back though. It was called the Digital Module R and could work with the R8 and R9 film SLR bodies. It was basically a new back and sensor plus booster section (akin to the canon PB-E2 booster), replacing much of the lower half of the camera. It had an APS-H sensor (1.37X).

http://www.dpreview.com/news/0306/03062502leicadigitalr9.asp
 
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