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12-28-2009, 08:39 AM   #1
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pentax smc M 50 on k2000

Please see the two images below. First one in Av mode 1/6 sec exposure, second one in M mode, 1.5 secs exposure calculated by pressing the +/- button. Why is the second image darker than the first even though it had a longer exposure? Both taken at aperture f2. I tried this again and the same thing happens, in manual mode the image is darker even though it has longer exposure. When I use a helios m42 lens, the same thing happens, the exposure is always above one second when pressing the +/- button, so all the images come out blurry. Are we not supposed to use the +/- button in k2000? Or am I doing something wrong?

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12-28-2009, 09:24 AM   #2
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Was the ISO set in manual to the same setting as it was in AV?
12-28-2009, 09:29 AM   #3
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ISO 200 for both the pics. Another couple of pics.
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Last edited by jasonbx; 12-28-2009 at 09:53 AM. Reason: Added more pics
12-28-2009, 10:07 AM   #4
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Av mode always shoots wide open on M lenses. My guess is that when you are out of Av mode, the lens is stopping down to whatever you have the aperture set to and thus needs a longer exposure. Also, double check that you don't have the EV set to +- 2 on either setting


Last edited by enoeske; 12-28-2009 at 10:25 AM.
12-28-2009, 10:12 AM   #5
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Since this is the M lens, so you need to use the aperture ring on the lens. Press AE-L button to meter the exposure once you have the aperture set on the lens. Also, if you use M mode, the ISO will not change (whatever you have set before). For the K10D, K20D and K7 use the green button instead of AE-L button.
12-28-2009, 10:23 AM   #6
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QuoteOriginally posted by enoeske Quote
Av mode always shoots wide open on M lenses. My guess is that when you are out of Av mode, the lens is stopping down to whatever you have the aperture set to and thus needs a longer exposure.
You are right in what you say, but in this case the numbers don't add up.
If, in AV mode he were shooting at an actual f1.4 for 1/6th" and in manual f2.0 at 1.5" then the darker picture still received substantially more light than the lighter one. 1/6th at f1.4 would be equal to 1/3rd at f2.0. That means the darker picture received 4.5 times the light that the lighter one did.
12-28-2009, 07:35 PM   #7
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QuoteOriginally posted by enoeske Quote
Av mode always shoots wide open on M lenses. My guess is that when you are out of Av mode, the lens is stopping down to whatever you have the aperture set to and thus needs a longer exposure.
I am shooting at f2 in both cases and its the maximum aperture this lens has.
12-28-2009, 09:06 PM   #8
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Im not seeing any EXIF info on the actual images. Can you post some images that exhibit the behavior with EXIF intact?

12-28-2009, 10:04 PM   #9
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My guess: in Av mode, auto ISO was engaged, so it cranked up ISO as high as it needed to get a good exposure. No idea why the second picture came out so dark, but I'm guessing it wasn't *really* at f/2.
12-29-2009, 01:05 AM   #10
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QuoteOriginally posted by Marc Sabatella Quote
My guess: in Av mode, auto ISO was engaged, so it cranked up ISO as high as it needed to get a good exposure. No idea why the second picture came out so dark, but I'm guessing it wasn't *really* at f/2.
ISO 200 for both pics. Aperture f2 used for both pics. Will upload pic with exif data somewhere else once I reach home. The forum here seems to strip out the exif data.
12-29-2009, 07:51 AM   #11
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Uploading images to picasa.






http://picasaweb.google.com/ml.jason/Misc
12-30-2009, 01:31 AM   #12
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Hm, I have K-m (aka K2000) and M 2/50 lens.
Are you sure the aperture ring is really set to f2?

Is number 2 under the red "diamond" mark? If number 2 is under the white ball then in fact you are using aperture f22 ('cause then 22 is under the red mark) and not f2 - that would explain why you get that dark images in M mode! In AV mode the cam always shoots M lenses wide open, regardless of aperture ring position, that's why you get good images in AV!

Aperture set to f2
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Aperture set to f22
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12-30-2009, 05:20 AM   #13
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You are right.I guess I messed with the apertures. It was working fine when I tested yesterday in manual mode.

Do you find it a little tough to mount this lens to the camera? I have to apply a lot of pressure to turn this into the mount.
12-30-2009, 10:17 AM   #14
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Hi, I find that mine is a little bit harder to mount than my DA or Sigma lens but not significantly worse.

On a side note does anymore have any problems with the focus at infinity? Mine seems to be blurry when I'm at the full end of the infinity location I seem to have to rotate the infinity position to the red line and not the diamond to get it in focus.
12-31-2009, 02:02 AM   #15
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QuoteOriginally posted by jasonbx Quote
Do you find it a little tough to mount this lens to the camera? I have to apply a lot of pressure to turn this into the mount.
Yes, I also need to apply more force to mount this lens.

QuoteOriginally posted by epqwerty Quote
On a side note does anymore have any problems with the focus at infinity?
I have, but probably because my lens is in a not so good condition... I can't turn the focus ring all the way to infinity mark, can't focus on very far objects.

Mine also have a "sticky aperture", so I can't really use apertures smaller than f4. With all these issues and me finding stop down metering and manual focusing a bit tiring, I don't use this lens at all...
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