This is why we
love our discussion group. Thanks for all the comments.
Here is my
understanding of the
differences between MK lenses and A lenses. I will give you some of my "dreams" in the end.
I suspect that the key
difference is how the aperture is operated in the A mode vs. in the the manual modes. I think that the aperture is
electronically operated in the A mode. Electronic operation is faster than mechanical operated aperture which is the case for M or K lenses.
Mechanical vs. electronic operation
I looked through one of my A lenses (the 50mm f1.2 one) from the front. When I click the shutter in the automatic modes, it first moved to the pre-assigned aperture and then moved to the smallest aperture and then move back to the largest aperture.
When I put the A lens in manual mode by moving the aperture ring, it functioned like a M or K lens. It is mechanically operated. In this case, the aperture moved to the pre-assigned aperture (based on the aperture ring instead of the number on the LED). Then it moved back to wide open. So the operations are different between the A mode and the manual mode.
Slower aperture operation?
When I moved the aperture ring from the "A" setting, the "A" lens worked exactly like a "M" or "M" lens. I believe that the mirror moved faster than the mechanical aperture.
Even though the "A" lens would close the aperture to the pre-set one (using aperture ring), the speed is slower than the mirror flip.
I think that this is why K M lenses only seem to work in the largeset aperture even the aperture does shrink (is this the right word?) during the operation. The mechical aperture just moved too slow (much faster than our eyes can recognize).
My tests
So I did some tests ( you can do that too) on my K10D. If you set the camera to "continuous shooting", it would shoot significantly faster in the AV, SV, P... modes than in M mode. Why? My hypothesis is that the mirror moves slower in the M mode to accommodate the slow speed of the mechanical aperture operation.
I also tested my MZ-5 and SF-1 cameras. They both have the uncrippled KAF mount. There seemed no speed differences between the M mode and the automatic modes. I suspect that this is due to slow speed of film cameras in winding films. I do not have any Pentax cameras that are faster.
Dreams
Now I have s ome new wishes/dreams. I wish that
1. Pentax could restore the uncrippled KAF mount (which seems unlikely);
2. create a new Ma mode (some sort) to allow the apertures in older M and K lenses to operated properly while permit photographers to manually dial in the proper aperture to the camera. It does not need to be a sperate function on the dial ring. It could be hidden and only allow geeks to access it. This would permit P-TTL function;
3. Even better, Pentax could make something similar to P-TTL? The camera can pre-shoot first and then shot again using proper speed or ISO? Given the speed of P-TTL, I believe that this is doable and will not be very slow.
These could be small tweaks and can be done with new firmware. Here is where my dream ends. I do not expect Pentax to update K10D firmware anymore...
I know I know. I am dreaming. But hey who would not dream from time to time?!