Leica M-D: Why is it not as thin as the Leica M6?
I've lost count of the number of times I've been asked why the M240 and its variations cannot be made to the same depth as the M3 or the M6—33mm instead of 37mm. The rear screen and associated gubbins was often cited as the reason for this discrepancy in the bulkier digital. So when the M-D was announced there were renewed gasps of disbelief that the dimensions were exactly the same as the M240. Surely, many reasoned, without the screen and all those buttons it should have been possible to shave 4mm off the depth of the camera.
Of course it isn't as simple as this. Take a look at this M6 picture and the film-plane symbol. That shows where the film (that is, the sensor) sits in relation to the back of the camera. There's not all that much space. But the distance from the film plane to the lens is absolutely necessary and must be reproduced on a digital camera with the sensor taking the place of the film.
Now, as can be readily acknowledged, a sensor and its electronics is much thicker than a strip of celluloid. It easily accounts for the 4mm difference, even when you take away the screen and all its circuitry. This isn't to say that a slight reduction in depth couldn't be achieved; after all, sensors are probably getting thinner as technology progresses. One day a sensor could indeed by as thin as a piece of celluloid. Perhaps, if Leica were starting from scratch, some depth saving could be made.
For the moment, however, the M-D is a niche product and I am sure that retooling to allow a thinner body would be uneconomical. I hope, though, that advances in sensor technology and the success of the M-D will combine to make some reappraisal possible.