Originally posted by dlacouture Well, I should have written "a false aperture is needed to fool the camera and enable P-TTL with m42".
But P-TTL could perfectly work with preset lenses (m42) without any aperture information, if only Pentax would make the tiny firmware fix needed for this.
I don't disagree, with M42 lenses do the preflash and assume nothing changes
Quote: And, moreover, P-TTL could be made fully functional with PK-m lenses, with the simple algorithm change here : do the metering flash once the lens is stopped-down, not before. So simple it's a wonder they didn't made it right from the *istD days.
this will make an unreasonable shutter delay because it requires the lens to stop down fully before the mirror moves, presently they both take place at the same time
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In fact, PK-m lenses could be fully supported (meaning Av and P-TTL) by the following behavior (could be added to the "Permit A ring" custom function):
- if a non-A manual lens is mounted (either m42 or PK-m, doesn't matter), then stop it down in permanence (so, the PK-m would behave just like a m42, enabling Av mode).
except that the stop down function takes power, the camera is designed to wide open meter not stop down
Quote: - DoF preview could open the lens for ease of focusing.
- P-TTL can now be enabled, and the metering flash will always occur while the lens is stopped down, so the reading will be accurate.
while it can work the camera is not designed this way, you are implying a reversal of logic where the camera does not hold the lens open while focusing, this would make the camera incompatible with A series lenses
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This is just a matter of moving the aperture actuator in the right place, so this should not drain the battery (except if a constant force is needed for this, but I don't think so).
i believe you are wrong here, if you consider that the priority must be to deal with A and not non A lenses, For A lenses it must hold the aperture open with no power, for non A lenses it is the opposite
Quote: In this case, the camera does not need to know the actual aperture used and the lens' aperture range, as both metering and actual recording will occur at the same physical aperture. That's what we do when tricking the camera with m42 lenses by selecting the greatest aperture available.
Another solution would be to stop down the lens on shutter half-press only, at metering time, but if the aperture is slow to close (oil on blade, etc), this could lead to exposure problems.
actually the best way is to enter the max and min aperture, and let the camera re-scale the activation lever to deal with the diameter linear with lever movement as opposed to area linear with lever movement, issue
Quote: OT : in the same time, it would be great if Pentax added the following tweaks (not P-TTL related):
- Enable trap focus with PK-m and m42 manual lenses when the body is set to AF (currently need to shorten the mount contact pins).
- Enable trap focus with all lenses when the body is set to MF and the user presses the AF button.