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03-11-2020, 03:39 PM - 1 Like   #16
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Thanks everyone for your comments!

QuoteOriginally posted by gofour3 Quote
Well done! I only shoot film so this is very interesting to me. I wonder if the Z-1/Z-1p film bodies can control the DFA* 50 f1.4 lenses aperture via the body like A/F/FA lenses?

Thanks, Phil.
For the reasons others have mentioned already, I can basically guarantee that the Z-1/Z-1p will not be able to control the electronic aperture of the DFA* 50. However, I don't know what to expect otherwise in terms of functionality with that combo. I don't see a reason why it wouldn't at least allow taking a picture, unless the Z-1/Z-1p gets some kind of unexpected info back from the lens and decides it cannot work with it. The reason why the LX is easier to understand is that it has no electrical communication with any lenses, so it is intuitive what will or will not work. Probably the only way to know the level of functionality of that combo is to directly test it. I would guess that AF will not work, you would need to put the camera in aperture-priority, and you would need to select f 1.4. The reason for this is that the Z-1/Z-1p will think it can stop the lens down, but it actually can't. Thus, if it is in any exposure mode besides manual or aperture-priority, you will likely end-up with a wildly incorrect exposure.

QuoteOriginally posted by kiwi_jono Quote
P.S. the corners of the film frame had me doing a double take for a moment (was obviously not vignetting as that would not look like that at f1.4) - LOL.
I didn't think to mention that. You are correct that the dark corners are from the slide frames, not vignetting.

QuoteOriginally posted by gylfimag Quote
Part of the beauty of the LX exposure system is that in auto mode (aperture priority) it does not matter if the camera can determine pre-exposure whether the lens is stopped down. The TTL system measures the light being reflected off the film during exposure and closes the shutter when the film is correctly exposed. This was state-of-the-art when the LX was introduced and basicallyl still is.
I was forgetting about this aspect of the LX. My assumption was that, because I was getting correct exposures, the opening on the DFA* 50's mount was in the correct place to indicate wide-open. However, if it was the case that the off-the-film metering was correcting for error indicated by the lens, my assumption could be incorrect. Testing would be needed on another aperture-priority-only body that has more standard metering, such as the ME Super.

QuoteOriginally posted by pentageek Quote
Definitely - you made me think about similar experiments. Opposite combination (new camera/old lens) is quite common, but here we have something Pentax engineers probably never envisioned
Not many tests are done with newer lenses on older bodies. There is a lot of potential there. I am also not sure that this compatibility was unintentional. They could have just as easily had the opening for the aperture indicator signal stopped-all-the-way-down as is the case with all other DFA lenses without aperture rings.

03-11-2020, 08:49 PM   #17
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QuoteOriginally posted by stevebrot Quote
Why would the charts indicate that? None of those older cameras had shutter or even flash sync interlocks.

In the chart all film cameras, including the LX, under the DFA 50/1.4 column have a red "X" indicating the "Although the lens fits the body, it cannot be used: The shutter will not fire (manual focus lens) or the lens cannot be focused (DA focus-by-wire lens)." The chart is incorrect and should be a purple "!", indicating "Not Recommended. Aperture will remain wide-open and cannot be controlled."

It's clear now some of these newer Pentax lenses have until now, never been tested on film cameras. The chart needs to be updated for the DFA 50/1.4.

03-12-2020, 03:28 AM   #18

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QuoteOriginally posted by stevebrot Quote
As with the K-3, the K-50 supports KAF4 with firmware update.

yes! Never understood, why they didn't also do the firmware update to the K-5 too
03-13-2020, 06:00 AM   #19
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You could always try a series of step down rings on the front to reduce the aperture - assuming aperture works this way? I've heard people do this for astro work to ensure a circular aperture .

03-13-2020, 06:16 AM   #20
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QuoteOriginally posted by johnha Quote
You could always try a series of step down rings on the front to reduce the aperture - assuming aperture works this way? I've heard people do this for astro work to ensure a circular aperture .
This is probably a thread derail but I would be interested in how to do that as well and not just end up with a really vignetted image instead. There's also the math required to use a step-down ring as a hood and not cause vignetting which isn't completely known to me (although I have working examples of such that I use often, I just don't know completely how to lay out the equation).

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