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05-27-2019, 12:53 PM - 1 Like   #1
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Continuous shooting with non-A lenses

Perhaps this has been noted and posted before, but it was new to me. Yesterday evening, I was confirming that continuous drive mode works with CIF* and noticed that the frame rate on "H" was downright slow (about half) with my XR Rikenon 50/2. I switched to a lens having the "A" contacts (camera controls aperture) and the rate was at the expected 8 fps. This happened in M mode with the speed set to 1/250s for both lenses.

Why might this be?


In case it might be a factor, my K-3 is early production (Nov 2013, SN 4867947) running firmware v1.30.


Steve


* PF info request


Last edited by stevebrot; 05-28-2019 at 09:35 AM. Reason: clarification
05-27-2019, 02:34 PM   #2
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Hmmm. That's interesting, Steve... Not something I've tried myself, but I'll endeavour to give it a go in coming days...
05-27-2019, 07:37 PM   #3
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Try flipping the focus mode to auto? I have the same lens (I think), Iíll try tomorrow
05-27-2019, 09:33 PM   #4
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Could it be that the K3 does not confirm focus as quickly with the XR Rikenon 50/2 lens as it does with other lenses?

Photobill

05-27-2019, 09:43 PM   #5
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QuoteOriginally posted by bobbotron Quote
Try flipping the focus mode to auto? I have the same lens (I think), I’ll try tomorrow
That was the setting when I discovered the behavior; I was doing CIF. I then tried a selection of my non-A K-mount, A-series, FA-series and adapted M42 lenses both in AF and MF setting.

Results:
  • Pentax K and M: slow
  • A-series on "A" position: expected speed
  • A-series using aperture ring: slow
  • FA-series: same as A-series
  • Adapted M42 (non-conductive base): expected speed


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05-27-2019, 11:00 PM   #6
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I haven't noticed any slow down with my M's with K30, K5 or K1, if there is enough light for fast AF lock.
05-28-2019, 09:31 AM   #7
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QuoteOriginally posted by Photobill Quote
Could it be that the K3 does not confirm focus as quickly with the XR Rikenon 50/2 lens as it does with other lenses?

Photobill
Does it when on MF too.

QuoteOriginally posted by iheiramo Quote
I haven't noticed any slow down with my M's with K30, K5 or K1, if there is enough light for fast AF lock.
Perhaps I should have been more explicit. What I noticed is a drop in frame rate when in continuous drive mode.


Steve

Last edited by stevebrot; 05-28-2019 at 09:36 AM.
05-28-2019, 10:24 AM   #8
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QuoteOriginally posted by stevebrot Quote
Perhaps I should have been more explicit. What I noticed is a drop in frame rate when in continuous drive mode.


Steve
That's also what I ment. Of course assuming good light so AF regognation works well. Also the fact that, if I don't notice something, doesn't necessary mean that it doesn't excist.

05-28-2019, 10:48 AM   #9
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Thanks Steve
Just out of curiosity with the Rikenon do you get a similar hit in frame rate with another body.
Regards
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05-28-2019, 02:11 PM   #10
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QuoteOriginally posted by Photobill Quote
Thanks Steve
Just out of curiosity with the Rikenon do you get a similar hit in frame rate with another body.
Regards
Photobill
I only have the K-3. I checked several other lenses (LINK). Using the aperture ring on a K-mount lens resulted in about half the expected frame rate as from when the body controls the aperture.


Steve
05-28-2019, 10:13 PM   #11
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QuoteOriginally posted by stevebrot Quote
I only have the K-3. I checked several other lenses (LINK). Using the aperture ring on a K-mount lens resulted in about half the expected frame rate as from when the body controls the aperture.


Steve
I just did the same test with my K3II with a couple of older lenses with aperture rings. I would say there is about 20/30% decrease in FPS. I will try the same test in the next day or two on my K20.

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05-29-2019, 06:36 AM   #12
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Unlike earlier film cameras, the K3 has no way to know the current manual aperture setting for a lens. On the 'A' setting, the camera reads the matrix from the rest of the pins to determine a len's min-max apertures and knows it can control aperture within that range from the camera body. So, unless the camera thinks it has an 'A' lens, I am guessing the camera is taking the time to re-check exposure between each frame. I suspect you either need to lock exposure or fool the camera into thinking you have a 'A' lens.

My K3 thinks all my lens are 'A' capable ('A' pin shorted with a bit of foil under the body's lens mount), and when using a lens or lens adapter without the aperture matrix contact points (e.g. extension tube), I insulate the aperture matrix pins appropriately with a bit of magic tape so the body knows the mounted lens' aperture range. Then you set the same aperture on the body and on the lens. Full disclosure: most images are correctly exposed using this hack, but I have seen exposure variations of less than 1/3 stop which are easily tweaked in post production. Test the lens before you shoot so you know.
05-29-2019, 07:48 AM   #13
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QuoteOriginally posted by JimJohnson Quote
I am guessing the camera is taking the time to re-check exposure between each frame. I suspect you either need to lock exposure or fool the camera into thinking you have a 'A' lens.
I did the test in M-mode (no metering).* I set the shutter speed above the X-sync so that would also not be an issue. I am thinking that it may have something to do with cycle lead times for the aperture actuator. Those are known when the body is in control, but unknown when using the aperture ring.


Steve

* AF time to detect is also not in the mix; while PDAF for CIF might be an issue, this happens when set for manual focus as well.
05-29-2019, 08:21 AM   #14
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QuoteOriginally posted by stevebrot Quote
I did the test in M-mode (no metering).* I set the shutter speed above the X-sync so that would also not be an issue. I am thinking that it may have something to do with cycle lead times for the aperture actuator. Those are known when the body is in control, but unknown when using the aperture ring.


Steve

* AF time to detect is also not in the mix; while PDAF for CIF might be an issue, this happens when set for manual focus as well.
Makes sense. Only way I know to test it, is to go the step further and fool the camera into thinking all lenses are in 'A' mode. There isn't a lot different mechanically between KM and KA lenses. While exposure might be off a bit by not telling the K3 the aperture range on the lens, it wouldn't take 5 minutes to temporarily short the A contact (stuff a tiny ball of aluminum foil into the hole on the body's lens mount) and see what happens when you repeat your fps test.
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