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11-26-2009, 01:33 PM   #1
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Av mode and M42 lenses

Is the Av mode supposed to always try to achieve 1/125s shutter speed or is it supposed to depend on the focal length you select?

My K-x seems to always try to get 1/125, if I select 600mm+ FL and if I select 8mm FL in good light. The ISO changes instead, and only at the limits of 100 and 12800 does it change the shutter.


Last edited by Eruditass; 11-27-2009 at 02:08 AM.
11-26-2009, 01:46 PM   #2
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QuoteOriginally posted by Eruditass Quote
Is the Av mode supposed to always try to achieve 1/125s shutter speed or is it supposed to depend on the focal length you select?

My K-x seems to always try to get 1/125, if I select 600mm+ FL and if I select 8mm FL in good light.
No matter the aperture?
11-26-2009, 06:56 PM   #3
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No matter the aperture, no matter the light coming in (which is effectively the same as changing the aperture since the body doesn't know the aperture).

I'm hoping this is a K-x bug and assume that all other Pentax's actually try to get a shutter speed based on the FL.

In addition, I noticed in M mode it doesn't meter the scene unless I assign the green button to optical preview and hold it down. Is this normal behavior as well?
11-26-2009, 07:02 PM   #4
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The camera is metering from the actual light coming into the lens, your FL should have nothing to do with the shutter speed.

Hummm....did you "enable aperature ring" in your settings?

11-26-2009, 07:06 PM   #5
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QuoteOriginally posted by Eruditass Quote
In addition, I noticed in M mode it doesn't meter the scene unless I assign the green button to optical preview and hold it down. Is this normal behavior as well?
As far as i know, yes.
my M series lens also does this.
11-26-2009, 07:34 PM   #6
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QuoteOriginally posted by Eruditass Quote
No matter the aperture, no matter the light coming in (which is effectively the same as changing the aperture since the body doesn't know the aperture).

I'm hoping this is a K-x bug and assume that all other Pentax's actually try to get a shutter speed based on the FL.

In addition, I noticed in M mode it doesn't meter the scene unless I assign the green button to optical preview and hold it down. Is this normal behavior as well?
All this is normal behaviour, not a bug. When using manual lenses on my K200D or K-x, in M mode, the camera only meters/calculates an exposure once the green button has been pressed. See the K-x manual at page 284: 'Notes on [22. Using Aperture Ring].

The way I use my M lenses is:

- I always set the mode dial to M,
- then compose the shot,
- set the aperture (or stick with a handy default),
- focus,
- press the Green button to get the camera to calculate the appropriate shutter speed (by stopping down to the indicated aperture), then
- press the shutter.

Works pretty reliably.

I have the Green button action in Manual mode set to Tv SHIFT [Menu 4 > Green Button > Action in M Mode > Tv SHIFT].

I think the default may be P LINE, but when using M series lenses the camera forces Tv SHIFT on you anyhow, since in M mode using M lenses there's no other real option other than to have the camera adjust the shutter speed, since it can't dynamically read or adjust the aperture like it can with A and newer lenses.
11-26-2009, 07:55 PM   #7
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I'm not talking about M series lenses, they are significantly different than M42 lenses which stop down as you turn the ring, and I use M lenses exactly as you describe, except I set the shutter before focusing. I assume you mean Av shift, where it sets the shutter, Tv would set the aperture.

The Av mode is not a bug? That's a pretty crappy implementation, then.

I know it is expected that in M mode it won't meter M-series lenses since it focuses and meters wide open. It just wouldn't make sense to have the meter on with a half press.

With M42 lenses that stop down as you turn the ring, it would make sense to do it. But it wouldn't be a big deal if Av actually worked like it should..

Many people said they prefer M42 lenses because they can use Av mode with more apertures than wide open, but it only half works at least on the K-x.
11-26-2009, 08:06 PM   #8
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Sorry - my bad re M42. That was a bit of copypasta from another post of mine on a related subject.

11-26-2009, 11:14 PM   #9
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Your camera is not reacting the way it should. It sounds like your aperture ring is not enabled. I shoot almost exclusively with M42s, but on an *ist DS. I imagine the control for your aperture should be somewhere in the custom menu. I don't know if this is your problem, but doublecheck it just to be sure.
11-26-2009, 11:19 PM   #10
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Does the M42 lens have an A and M setting?

If so set the lens to M.

As you turn the aperture ring, you should be able to see the lens stop down. If you do not see this, the camera will not know that the aperture has changed. The viewfinder should get darker as well.

Remember that the M42 lenses have a pin that is pushed in to close the aperture. Modern K mount cameras do not have the linkage to work with the pin. You need to set the lens to "M"

Edit:

The setting of focal length has nothing to do with exposure. It is how the camera knows what lens is on it so the SR functions.
11-26-2009, 11:36 PM   #11
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I'm starting to get confused!

I haven't had a PK or M42 lens on my K20 for a while.
In AV mode the camera should give you a ball park idea of metering with these lenses attached.....right?
I'll give it a go tomorrow.

Cheers,
Ray
11-26-2009, 11:44 PM   #12
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QuoteOriginally posted by raymeedc Quote
Your camera is not reacting the way it should. It sounds like your aperture ring is not enabled. I shoot almost exclusively with M42s, but on an *ist DS. I imagine the control for your aperture should be somewhere in the custom menu. I don't know if this is your problem, but doublecheck it just to be sure.

This sounds right to me.

IIRC the camera SHOULD change shutter speeds as you step the aperature up or down in AV mode.
11-26-2009, 11:56 PM   #13
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QuoteOriginally posted by Eruditass Quote
I'm not talking about M series lenses, they are significantly different than M42 lenses which stop down as you turn the ring, and I use M lenses exactly as you describe, except I set the shutter before focusing. I assume you mean Av shift, where it sets the shutter, Tv would set the aperture.

The Av mode is not a bug? That's a pretty crappy implementation, then.

I know it is expected that in M mode it won't meter M-series lenses since it focuses and meters wide open. It just wouldn't make sense to have the meter on with a half press.

With M42 lenses that stop down as you turn the ring, it would make sense to do it. But it wouldn't be a big deal if Av actually worked like it should..

Many people said they prefer M42 lenses because they can use Av mode with more apertures than wide open, but it only half works at least on the K-x.

For an example.

With your M42 attached to your Kx (aperture not important) and you have a very different scene with shadows and brighter bits, your shutter button is depressed half way, moving your camera from the shadow areas to the bright parts the shutter speed does not change from 1/125?
11-27-2009, 01:59 AM   #14
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...

I mention the light coming into the sensor is different and how opposed to only stopping down while shooting, M42 lenses stop down as you turn the ring (thus of course my lens is stopping down and doesn't stay wide open as if it were on A), but the shutter speed is the same. I should've also mentioned that in Av mode it is changing the ISO, from say 200 to 12800 to compensate for the aperture ring turning and keeping the shutter locked at 1/125. And of course the viewfinder gets darker.

QuoteOriginally posted by Raybo Quote
The camera is metering from the actual light coming into the lens, your FL should have nothing to do with the shutter speed.

Hummm....did you "enable aperature ring" in your settings?
Yes it should, at least in Av mode. As opposed to arbitrarily choosing a shutter speed to aim for, it could actually be intelligent and pick a suitable shutter speed in the least, or just copy the intelligent ISO/shutter shifting of normal Av mode.

That menu setting prevents you from even taking a picture.

Last edited by Eruditass; 11-27-2009 at 02:13 AM.
11-27-2009, 02:02 AM   #15
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QuoteOriginally posted by KungPOW Quote
The setting of focal length has nothing to do with exposure. It is how the camera knows what lens is on it so the SR functions.
but it should have an effect in Av mode, as in Av mode with lenses that transmit focal length. I know it is for SR, but logically, it should also use it for an approximate shutter speed to aim for, as it does in "real" Av mode. I'm just trying to confirm whether or not all Pentax cameras are all dumb in Av mode, even though M42 lenses are touted for their ease of use due to Av mode.
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