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12-21-2019, 11:59 AM   #16
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QuoteOriginally posted by Hawkfan Quote
Also it does appear that in AV, the camera shoots wide open no matter the F-stop set on lens. Is this "normal"?
I don't think so. If you have an f/4 lens set to f/11, the aperture will stop down to f/11 when you press the button. This is done via a mechanical link between the lens and camera. The shutter speed will be set the value for f/4 though, leading to an underexposed image.

The reason for all this is that modern Pentax bodies do have the link needed to detect what the aperture ring on your olde M lens is set to. See "crippled K mount" for more detail. It started out as a cost cutting measure in the film era. It must have seemed like a good idea at the time...


Last edited by Wasp; 12-21-2019 at 02:13 PM. Reason: typo
12-21-2019, 12:19 PM   #17
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QuoteOriginally posted by grog85361 Quote
The KX doesn't give you that option. Also, in M exposure mode, exposure compensation, even if set in another mode, has no effect.

I have been trying to duplicate your problem with my KX, but when I adjust the exposure to "0", it is right on. I would suspect a problem with your lens, since the DA lens works properly. Do you have other M lenses to try? This is a stumper. Best of luck.

---------- Post added 12-21-19 at 11:36 AM ----------

What aperture is your lens ring set to? In your second sample, a shutter speed of 1/2000 with ISO 200 would be appropriate for a very open aperture, like around f4.
F8 was setting on lens. While I do have several other K and M lenses, they are in storage right now in another state so I can not access for awhile. I guess I will have to wait a bit until I can grab another lens.

---------- Post added 12-21-19 at 12:40 PM ----------

I have taken lens off and and I think I was presumptuous in stating it was snappy. Upon inspection, it appears slow to close. I suspect this may be causing the intermittent results. I will access another old manual lens when I am able but it will not be possible to get to where they are stored for awhile. I will report back. I do wish to thank the respondents. What a great community.
12-21-2019, 12:56 PM   #18
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If that's the case, there's a quick check: Set the lens to f/22 (or whatever minimum it is), and a suitably long exposure. Take a selfie and see if the blades close quickly.
12-21-2019, 01:00 PM   #19
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The lens will only stop down to the setting on the aperture ring in Manual mode when you press the green button, operate the optical DOF or release the shutter. The iris will stop down in B or X mode when you use the optical DOF preview or take an exposure.

In Manual mode when you press the green button the iris stops down to the ring setting, the camera takes a meter reading and sets the appropriate shutter speed. When press the shutter release the lens stops down to the ring setting and takes the exposure at the shutter speed set by the green button.

On "flagship models" (K10D/20D, K-7, K-5, K-3, K-1) if you operate the optical DOF preview the lens stops down and the EV is shown as a bar meter and you can zero the EV by turning the eDial for the shutter speed or change the aperture with the aperture ring. Pressing the shutter release stops down the lens to the ring setting and uses the shutter speed set by the eDial.

Pressing the green button in Av mode should do nothing unless you programmed the green button to do something else.


Last edited by Not a Number; 12-21-2019 at 01:06 PM.
12-21-2019, 01:37 PM   #20
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In my K-X, the green button is set to P-line in M mode.

When I press the AV button in M Mode the lens stops down to the ring setting and sets the correct shutter speed. It is the same behaviour as I press the green button.
12-21-2019, 02:02 PM   #21
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IIRC the k-x uses the AE-L button as It's "green button". But acts the same when the camera is in M mode. It stops the lens down for a reading then calculates shutter speed. In the OP's case, a sticky or slow lens aperture would cause the overexposures he's seeing.
12-21-2019, 02:09 PM   #22
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QuoteOriginally posted by Hawkfan Quote
Also it does appear that in AV, the camera shoots wide open no matter the F-stop set on lens. Is this "normal"?
Yes, this is normal. M and B modes are the only modes on your camera where the lens will stop down to a value set on the aperture ring.


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12-21-2019, 02:55 PM   #23
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QuoteOriginally posted by paulh Quote
IIRC the k-x uses the AE-L button as It's "green button". But acts the same when the camera is in M mode. It stops the lens down for a reading then calculates shutter speed. In the OP's case, a sticky or slow lens aperture would cause the overexposures he's seeing.
The K-X has its own green button. The older cameras as the ist series do not have green button.

12-21-2019, 03:02 PM   #24
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QuoteOriginally posted by Not a Number Quote
The lens will only stop down to the setting on the aperture ring in Manual mode when you press the green button, operate the optical DOF or release the shutter. The iris will stop down in B or X mode when you use the optical DOF preview or take an exposure.

In Manual mode when you press the green button the iris stops down to the ring setting, the camera takes a meter reading and sets the appropriate shutter speed. When press the shutter release the lens stops down to the ring setting and takes the exposure at the shutter speed set by the green button.

On "flagship models" (K10D/20D, K-7, K-5, K-3, K-1) if you operate the optical DOF preview the lens stops down and the EV is shown as a bar meter and you can zero the EV by turning the eDial for the shutter speed or change the aperture with the aperture ring. Pressing the shutter release stops down the lens to the ring setting and uses the shutter speed set by the eDial.

Pressing the green button in Av mode should do nothing unless you programmed the green button to do something else.
Correct. The lens stops down when green button pressed in M mode. No function in Av mode.

---------- Post added 12-21-19 at 03:25 PM ----------

QuoteOriginally posted by dantonvb Quote
In my K-X, the green button is set to P-line in M mode.

When I press the AV button in M Mode the lens stops down to the ring setting and sets the correct shutter speed. It is the same behaviour as I press the green button.
Odd, as my K-X has no P-Line setting for green button.
12-21-2019, 03:26 PM   #25
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I checked my k-x and *ist DL. In k-x we can use the green button or the AV button to obtain the correct shutter speed automatically, in M mode with a lens with aperture ring. In *ist DL the button to be used is the AE-L button. Same result in both cameras, the shutter speed set correctly.

---------- Post added 12-21-19 at 03:31 PM ----------

QuoteOriginally posted by Hawkfan Quote
Odd, as my K-X has no P-Line setting for green button.
You have to set Green Button function to Green Button, and not to Optical Preview. Then it will appear two options bellow Green Button. One for M Mode and other for Program Mode.

Last edited by dantonvb; 12-23-2019 at 03:23 AM.
12-21-2019, 05:10 PM   #26
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QuoteOriginally posted by dantonvb Quote
I check my k-x and *ist DL. In k-x we can use the green button or the AV button to obtain the correct shutter speed automatically, in M mode with a lens with aperture ring. In *ist DL the button to be used is the AE-L button. Same result in both cameras, the shutter speed set correctly.

---------- Post added 12-21-19 at 03:31 PM ----------



You have to set Green Button function to Green Button, and not to Optical Preview. Then it will appear two options bellow Green Button. One for M Mode and other for Program Mode.
OK, I see it in menu. So can you explain what exactley the P-Line setting does? What is Program Line?
12-21-2019, 05:59 PM   #27
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QuoteOriginally posted by Hawkfan Quote
OK, I see it in menu. So can you explain what exactley the P-Line setting does? What is Program Line?
The camera has a combination (shutter) of shutter speed and aperture for each exposure value (EV) programmed in memory. Think of EV as the amount of light or brightness of the scene. The program line is this set, recommended for the situation.
This article explain this in detail: Pentax Green Button Guide - Articles and Tips | PentaxForums.com

See the graph in the article to understand.

When the camera is in manual mode M, with a lens without aperture ring or lens with aperture ring in position A, the green button sets the aperture and shutter speed according to the program line. If the lens has an aperture ring out of position A or an M or K lens, the green button sets the shutter speed for the aperture selected on the lens.

Last edited by dantonvb; 12-22-2019 at 04:46 AM.
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