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12-15-2023, 10:18 AM   #1
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Pentax K-X and SMC Pentax-A 50mm. f/1.7 question

Good day,

I've mounted my SMC Pentax-A 50mm. f/1.7 on my new old Pentax K-X to figure out manual exposure and focusing.

What I observe is that when I put the camera in manual mode and press the AV button to get an exposure reading, deviating from the proposed shutter value doesn't result in showing the -0.3 or +0.3 et cetera under or over exposure value in the view finder.

Why is that? Is this because there's no electronic communication with the lens? ISO value is fixed to 200. Aperture is f/5.6. Switch on the camera body is "MF".

Thanks!

Best,

Robert.


Last edited by Robert1966; 12-15-2023 at 10:31 AM.
12-15-2023, 12:05 PM   #2
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This is how manual mode with an "A" lens (SMC Pentax-A 50mm f1.4) aperture set at "A".
Note: Exposure compensation is disabled in manual mode

Activate meter:
Set desired aperture with eDial e.g. 5.6
either press the green button (camera will set the shutter speed, e.g. 200) and adjust the shutter speed with the eDial using exposure bars of the meter over or under from 0 (zero).
or
set the shutter speed with eDial to over or under from zero on the exposure bars.

Make sure the EV setting in setup is 1/3 if that's you want (vs 1/2).
12-15-2023, 02:38 PM   #3
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It sounds like the OP is using the aperture ring on the lens to set the aperture in order to emulate an older, pre-A lens.

I don't have a K-X, but on the K1, with the camera in manual mode and the lens aperture ring set to f5.6, pressing the green button will set the shutter speed to what it thinks is correct.
It does not show an over/under bar since the shutter speed should now be "correct".

If you change the shutter speed, it does not update the bar because it has not stopped down to take another meter reading.
It assumes you know what you are doing

So it sounds like your K-X is working as intended... even if it is a bit inconvenient...

If you leave the lens in A, you'll get the more expected manual behavior, since it knows what the aperture is doing at all times.

-Eric
12-15-2023, 03:07 PM   #4
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The first question is, is the lens in the A position or is he adjusting aperture manually

If he is using the lens aperture manually then he has to set the function Use Aperture Ring to on. Not sure how to navigate to that function on the K-X

But, if thenOPmputs the lens in the A position, the lens should behave just like any newer lens, and all the same functions should be available

12-16-2023, 06:01 AM   #5
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@TwoUptons: the bar is not updated when changing the shutter speed, that sounds reasonable to me, thanks for the info!
12-16-2023, 10:46 AM   #6
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QuoteOriginally posted by Robert1966 Quote
@TwoUptons: the bar is not updated when changing the shutter speed, that sounds reasonable to me, thanks for the info!
If your lens has an aperture ring with the "A" setting, just leave the aperture ring set there. You then get full aperture control from the body in all modes without the need to use stop-down metering.
12-17-2023, 02:06 AM   #7
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Thanks, I know, but I wanted to know how things work when you don't have the lens on "A", like with a Pentax-M lens for instance.

12-17-2023, 07:00 AM - 1 Like   #8
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QuoteOriginally posted by Robert1966 Quote
Thanks, I know, but I wanted to know how things work when you don't have the lens on "A", like with a Pentax-M lens for instance.
1. Change the menu setting to "allow aperture ring"

2. Use Manual exposure mode only. Either press the AE-L button to make the camera stop down and select a shutter speed, OR turn and hold the DOF preview switch (needs to be on the default Optical Preview) to turn on the meter. Adjust either shutter speed or aperture ring to get desired reading.

3. You can also use a non-"A" lens in Av mode but it will only capture wide open.

4. Any other auto mode (Tv/TAv/P) will default to Av and only capture wide open.

Last edited by pschlute; 12-18-2023 at 12:58 AM.
12-17-2023, 07:49 PM - 1 Like   #9
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QuoteOriginally posted by pschlute Quote
1. Change the menu setting to "allow aperture ring"

2. Use Manual exposure mode only. Either press the AE-L button to make the camera stop down and select a shutter speed, OR turn and hold the DOF preview switch (needs to be on the default Optical Preview) to turn on the meter. Adjust either shutter speed or aperture ring to get desired reading.

3. You can also use a non-"A" lens in Av mode but it will only capture wide open.

4. Ay other auto mode (Tv/TAv/P) will default to Av and only capture wide open.
Everytime I saw such thorough and practical instructions for certain issues that are aroused quite often among new users, I say to myself if only there was a SAVE button besides it and I can collect all those insights into one place. Just a thought, haha.
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