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07-09-2008, 12:24 AM   #1
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M lenses in Av mode

Today I was playing with my Hoya 135 M lens. I always thought it's a pitty you can't use M lenses in Av mode. Then I read thread from Gooshin about snipping the apperture lever off. So you can use M lens in Av and camera will meter correctly. And then I thought....
Some clever people included something called exposure compensation in our cameras. So what if you want to use manual prime (or any other M lens for that matter) in Av mode, on it's best f stop (let's say 1 or 2 down from wide open). YOU CAN! All you need to do is, if you stop the lens 1 stop down, just dial +1 Ev - this will compensate for the metering wide open and simulates metering 1 stop down on the lens! the picture should come witch correct exposure...
I'll have to play around with Hoya bit more to see if it works correctly....
Any insights welcome....

07-09-2008, 01:08 AM   #2
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In Av mode the aperture will stay wide open during the shot, no matter what you dial in on the aperture ring.

PS. : Hoya lens on a (now owned by) Hoya camera, ain't it nice
07-09-2008, 01:53 AM   #3
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I agree with procyon, it is not just that the camera meters meters wide open in Av mode with M &"K" lenses, it captures wide open too.

if you perform surgery on your lens you can get it to behave like the M42 lenses in that it will stop down as you turn the aperture ring. You can then use Ev mode correctly. The downside of course is that the viewfinder gets very dark at small apertures.
07-09-2008, 02:10 AM   #4
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Do you want your M lenses to work as an A lens in Av mode?

Here is what you have to do.

When you put the lens on the mount, do not turn it full until it locks in, but stop a litlle before that (so that the red point on the lens is somewhere in the area of the letter P on the Pentax writing on the flash).

Go it?

Now turn the camera on an you can use it normali in the Av mode.

The blades now close as you turn the aperture ring and so the camera can meassure the exposure corectly (often you have to compensate +0.3 or +0.7).

Matej

07-09-2008, 05:45 AM   #5
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Where on earth did you guys get the idea that M lenses won't shut down the aperture if the camera is in Av mode?
07-09-2008, 05:59 AM   #6
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K mount M lenses or M42 M lenses???
07-09-2008, 06:18 AM   #7
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QuoteOriginally posted by Mike Cash Quote
Where on earth did you guys get the idea that M lenses won't shut down the aperture if the camera is in Av mode?
M as in SMC Pentax-M lenses (with K-mount) can only be used with fully open aperture in Av mode.
I suspect you meant M42 lenses? These can of course be used at any aperture.
07-09-2008, 06:51 AM   #8
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QuoteOriginally posted by procyon Quote
M as in SMC Pentax-M lenses (with K-mount) can only be used with fully open aperture in Av mode.
I suspect you meant M42 lenses? These can of course be used at any aperture.
No....I meant M lenses.

The aperture coupling armature doesn't care what mode your camera is in. It even operates when using M42 lenses, though there is no part of the lens contacting it.

M lenses will only meter fully open in Av mode. But mechanically the lenses do stop down if you attempt to shoot with them in Av mode. Of course, the metering is all wrong so there's no point to it.

You said the iris will stay fully open in Av mode, no matter what aperture is set on the aperture dial, and that is not the case.

07-09-2008, 07:06 AM   #9
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QuoteOriginally posted by Mike Cash Quote
No....I meant M lenses.

The aperture coupling armature doesn't care what mode your camera is in. It even operates when using M42 lenses, though there is no part of the lens contacting it.

M lenses will only meter fully open in Av mode. But mechanically the lenses do stop down if you attempt to shoot with them in Av mode. Of course, the metering is all wrong so there's no point to it.

You said the iris will stay fully open in Av mode, no matter what aperture is set on the aperture dial, and that is not the case.
I just made a quick test.
K10D with M 50 f/1.7
Camera in Av mode, no exposure compensation.
Shot 3 pictures.
@ f1.7
@f8
@f22
All look exactly the same. No exposure difference. Shutter value is exactly same.
BTW if I look in the lens while taking the picture it seems to stop down, but it seems to have no effect...maybe it happens too early or too late.
I'll check with another lens soon.
07-09-2008, 07:23 AM   #10
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I did some further testing.
My Hoya lens also gives same exposure regardless of aperture ring in Av mode. The aperture is too far in the lens, so I can't say for sure whether it moves.
I used +3 exposure compensation with my M 50 and now I could see clearly that the aperture closes but immediately after the shutter has closed. So either both my lenses are broken, or my camera is broken, or ???
Btw. my manual lenses work perfectly with my camera in M mode.
07-09-2008, 07:28 AM   #11
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I know I can take pictures in Av mode wide open using manual K mount lenses without the "A" setting. I was under the impression that if I wanted to user smaller aperture settings I needed shoot in "M" mode (on my K100Ds) and use the AE-L button to stop down and meter correctly.
07-09-2008, 07:56 AM   #12
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QuoteOriginally posted by Mike Cash Quote
M lenses will only meter fully open in Av mode. But mechanically the lenses do stop down if you attempt to shoot with them in Av mode. Of course, the metering is all wrong so there's no point to it.
No the metering is not all wrong. It is right for the lens fully open! The point is that the exposure that you see in the VF is the one calculated for the current aperture which is fully open. For my K100D, the camera uses this exposure (or one calculated in the same way) when it takes the photo. In Av mode, when the K100D sees that I have a K or M lens it basically gives up trying to work out what aperture I have set, and treats it as being fully open all the time. M42 lenses work in Av mode because the K100D does not open the diaphragm fully open (it cannot) so whatever aperture I set is treated by the camera as being "fully open".

QuoteOriginally posted by Mike Cash Quote
You said the iris will stay fully open in Av mode, no matter what aperture is set on the aperture dial, and that is not the case.
Well I must have a faulty K100D because in Av mode if I set my M135 to f/16 and use the optical DOF preview the diaphragm stays fully open, but if I use M mode and use optical DOF the camera stops the lens down to f/16. (I have the appropriate custom menu setting.) Similarly, in Av mode if I set the M135 to f/16 the VF shows 1/180 (metering fully open) when I take a photo and look at the EXIF the shutter speed is given as 1/180, so the camera did not stop down before taking the photo. However, if I use M mode, the camera does stop down before taking the photo, but I have to make sure that I use the AE-L button before so that the camera meters at the specified aperture and calculates the shutter accordingly (in this case 1/4).

This is how my K100D works, is it faulty?

Richard
07-09-2008, 08:34 AM   #13
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Once more:

Turn the lens for one inch to the right and use it as an A lens in Av mode!!! Seriously it works and lens doe not fall off!

And you will have no trouble with meetering anymore.

matej
07-09-2008, 08:41 AM   #14
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QuoteOriginally posted by pikipoki Quote
Once more:

Turn the lens for one inch to the right and use it as an A lens in Av mode!!! Seriously it works and lens doe not fall off!

And you will have no trouble with meetering anymore.

matej
It will be like M42 lens in Av mode not like A lens.
You have to manually stop down M42 lenses in Av mode after focussing or as an alternative focus with the lens already stopped down (hard to focus).
But A lenses stay fully open in Av mode and close down to selected aperture only when you actually take the picture.
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