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Forum: Pentax SLR Lens Discussion
08-22-2018, 05:48 PM
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Good question. P-TTL with A-series lenses is less reliable due to apparent preflash at maximum intensity* and fail-over to full intensity when close, large aperture, and/or high ISO. There is no harm done in trying. You could see if having just the "A" contact taped would be adequate or if two other contacts must be made to provide equivalence to a known combination (LINK).
Steve
* Anecdotal based on personal inquiry
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Forum: Pentax SLR Lens Discussion
07-16-2018, 09:25 PM
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Because, depending on lens and set aperture, exposure may be wildly off. My K-3 works pretty well for stop-down metering with several lenses and not so well with others. Hacking the mount contacts is seen as a way to fool the camera into metering properly. It can work pretty well from the metering end of things, but automatic aperture control by the body does not work so well.
Steve
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Forum: Pentax SLR Lens Discussion
07-16-2018, 09:31 AM
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...qualified a bit to say that very few lenses without "A" contacts on the mount have a properly calibrated aperture mechanism. It is rumored that some late production M-series lenses are that way, meaning that a standard amount of movement of the aperture actuator results in the appropriate change in relative aperture (f-number or fraction thereof). Unusually this requires a cam mechanism specific to the iris size.
Steve
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Forum: Pentax SLR Lens Discussion
07-16-2018, 09:04 AM
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This has been tried before by more than one forum member, but never with fully favorable results. The best utility was that metered exposure settings would be accurate and that they could be used for full manual exposure in M mode using a combination of aperture ring on the lens and minimum aperture on the camera.
Steve
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