Focus confirmation in a future M

[adan]

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Let me just add that for me, this is an interesting engineering exercise, but with no real point in the real world.

 

The M viewfinder/rangefinder, exactly as it is, is why I use the system. If it doesn't work for some people, there are plenty of other cameras to choose from that may work better - for them.

 

Personally, I can take off my glasses and still focus the resulting very fuzzy RF images with a 75 f/2 @ f/2 90% of the time - using "contrast detect" or other clues.

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[giordano]

John, are you familiar with the metering arm used in the M5 and CL cameras? It had no back-and-forth movement at all. Instead it moved up and down in an arc parallel to the camera body, so it needed no more depth than its actual thickness (plus a mm or so leeway).

 

Yes - and I wouldn't trust the swinging mechanism (even beefed up a bit) to retain micron precision.

Just replace the big CDS cell with a mirror about 3mm x 3mm and tilted forward.

I think the mirror would have to be bigger than 3mm x 3mm to direct light from near the periphery of the lens onto the focus sensor. The secondary mirrors in SLRs seem to be somewhat bigger than that - and see the sketch below.

The AF sensor wouldn't move at all. It would be fixed in the bottom of the camera mount, just as the flash-exposure sensor is in ttl M bodies (or AF sensors are in SLRs)

The light path from the lens via the mirror to the focus sensor has of course to be exactly the same length as that from the lens to the image sensor. This means that the closer the mirror is to the image sensor, the closer the focus sensor has to be to the optical axis. My sketch suggests that if the mirror is placed far enough back to allow the same choice of lenses as an M5, the focus sensor will be in the light path between a fast lens and the sensor - so will itself have to be moved out of the way before exposure - more precision engineering problems.

 

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[ohnri]

A CDAF system would be very helpful and could be used to calibrate the RF to each lens.

 

An electronic linkage between the lens mount and the RF prism would allow a drive-by-wire system that would allow the camera to focus perfectly for every lens once the simple initial calibration was performed.

 

Operationally, focusing would remain identical to the present experience with an all optical VF and RF.

 

Reliability and precision would increase.

 

Best,

 

Bill

[adan]

OK - I see your point(s). I might quibble with the size you've drawn your generic "lens" and whether there is some leeway for the sensor to stick up in a permanent position without blocking the image area. And I guess the whole mirror/sensor stack could drop vertically like a sub's periscope, but that would likely require a taller body. Or of course the focus spot could be lower than the center of the image (higher in the frame).

 

The good news is at least we are discussing real engineering, not just "I want it - make it happen."

[giordano]

The good news is at least we are discussing real engineering, not just "I want it - make it happen."

 

[diogenis]

Actually, like Adan explains there is no need to discuss engineering the mechanism, because we don't have the means to do so. There are many factors involved, and experts in the field, like Leica can solve the issue. Main thing here is to first find a necessity for such a mechanism.

 

I don't want an auto focus mechanism on an M because I can;t use the manual rangefinder.

I want the mechanism to stay as it is and a retrofit that will assure me of precision focusing under some difficult occasions, or when my eyesight becomes more demanding.

 

This will also give a pseudo feeling of technology to people like Zlatkob and others that believe that technology and advancement is in microelectronics.

In any case a somewhat "servo" focusing mechanism will eventually be a good thing just as we use servo breaks/steering in our cars.

 

Real question is, do you want a mechanism that will help you even more and be a little faster with moving subjects? Or a mechanism that is gonna be a bit more user friendly for when age takes over good eyesight? I vote yes