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05-09-2012, 03:22 PM   #1
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Why no metering when we press the shutter on old lenses?

So, by using the green button, we can pre-meter in manual mode. This lets us meter with K and M series lenses. But we have to do it ahead of time.

Why isn't there a mode (Av? Green?) wherein we set the aperture on the lens, and then by pressing the shutter:
  1. The lens is stopped down
  2. The camera meters the scene per settings
  3. The photo is captured

Obviously, this would delay the shutter a little bit as the metering happens, but if this were in a separate mode from manual, it would only add to our options, right?

05-09-2012, 03:27 PM   #2
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Probably because a. there would be a delay, as you mentioned, b. it would not be a mainstream feature.

It would be nice if they could just release a non-crippled DSLR other than the 645D.

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05-10-2012, 04:44 AM   #3
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Well I was thinking in similar directions, but my "solution" does not have to be a HW one.

As far as I understood, the K and M lenses have same (similar) mechanical aperture coupling as A lenses. What they don't have is electrical coupling telling the body the capabilites of the lens (effective maximum and minimum apertures). The aperture opening is then obtained by moving of the aperture lever. In case with new bodies, the lever is not moved all the way, but rather moved a "bit" thus choosing the aperture.

Moreover the choice of aperture in-camera (i.e in A mode on A lenses and newer) just tells the camera by how much the aperture lever should be moved once tha shutter is pressed. In that matter there is actually nothing that crippled KAF mount could do which the non-crippled counterpart can except that it can not read the apperture setting on the ring nor the capabilities of the lens (max and min apertures).

The "obvious" soulution would be to enter the aperture cababilites of the manual lens once the lens is inserted, perhaps in a similar fashion like the focal length is entered. Then the lens could be set to minimum aperture and the aperture could then be set in camera. The main advantage is that all modes could be used on old (non-A) lenses with aperture lever, and we wouldn't be limited only to M mode. This "trick" wouldn't work on M42 or lenses with completely manual iris (no aperture lever), but even in that case we could use lenses similarly as we do today in "A" mode since camera does the metering prior to the shot.

I hope that this makes sense.
05-10-2012, 06:46 AM   #4
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A simpler (but really neat) solution would be to stop-down the lens on half-press, and keep it stopped down until you fully depress the shutter (or release it to wide-open if you enabled AEL on half-press)...

This way, manual focus would be easily made wide-open before the half-press, then the camera stops-down and meters the scene live while you half-press the shutter, giving you a real-time metering.

Bonus point : P-TTL could be enabled with this solution (as it's basically what the DIY aluminum foil trick does).

Only difference with an actual A lens would be in the residual duration of metering after an half-press is aborted : currently, the camera keeps metering for 10-30s, but with this solution it would stops as soon as you release the half-press...


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