A screw mount lens will be stopped down when mounted. A K/M lens will be wide open regardless of aperture set on the lens. Hence, the camera need to stop down (with a motor) when metering with the latter. How does it know it is a K/M lens and not a screw mount lens?REPLY:
The camera need not know whether the lens is screw mount or k-mount. If the lens is screw mount, then it is already stopped down and the camera trying to close the aperture has no effect. If the lens is k-mount DOF preview stops down the lens.
This will be an awful solution both technically and in use only to please extremely few users.REPLY:
This is what is already is implemented in *ist and *ist D (unfortunately without metering when DOF preview is activated). It is not an awful solution but straightforward.
What if you forget to active DOF preview when metering?REPLY:
With a lens not in "A" position, metering should only be ON when DOF preview is activated. Actually, this would probably save battery power.
What if you accidentally use the same procedure with an FA lens out of habit?REPLY:
With an FA lens in A position, the meter should be OFF when DOF previewing. With the same lens not in "A" position, the meter should only be ON when DOF previewing. Quite simple, isn't it? How can you confuse the meter being ON or OFF?
Is the exposure value remembered by the camera or are stucked in manual mode only? If it use exposure lock then the camera must be designed so that it locks the metered value when activating DOF preview only with K/M lenses.REPLY:
See above: With a lens in "A" position, there is (and should be) no metering when DOF previewing. With any lens (FA, F, A, K, M, screw) not being in "A" position, metering should only be active when DOF previewing, and the measured value could be locked when DOF preview is ended.
The idea is probbaly to make a camera thats easy to use. The above make it truly crippled not to mention confusing.
REPLY: I hope your confusion is cured by now.
Pentax really had three choices. 1) Stick to the old KAF2 mount. 2) KAF2 with "electronic" metering . 3) Two separate metering systems 1)+2). 1) would probably make the *ist D incompatible with future lenses hence doing the customers no favour. 2) is what they did. 3) would be both awkward in engineering and expensive.REPLY:
It would only cost a few hours of programming and rewriting instrucion manuals. Stop-down metering as described by me would neither require any changes in the hardware nor would it complicate the use of the camera. On the contrary: The camera would be much easier to use with the built-in meter than without it.
Customers won't pay for it.REPLY:
Customers would not need to pay for it as it wouldn't have costed anything extra if Pentax had thought of it in the first place, and to update the camera software now would be payed for a lot of times by the extra cameras that would be sold, even if it were just a few.
Arnold
