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02-13-2013, 09:36 PM   #1
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Exposure with Pentax Kx

I just tested 3 lenses (1 Tamron and 2 'A') with my Pentax Kx in Av mode, at 2.8 - 5.6 - 11.
With every lense, the image is overexposed at 5.6 and underexposed at 2.8 and 11!!!
That could explain my disappointing photos during my last vacation...
Did you experience the same problem? Why is it happening? Can I do something to fix it?

Yves


Last edited by Belgarchi; 02-13-2013 at 10:00 PM.
02-13-2013, 10:58 PM   #2
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Keeping focus and exposure in center is what works for me plus paying attention to what I am getting by keeping check on the image in the lcd.Using a lens hood will help in a lot of cases.Use exposure correction in camera when needed.
02-14-2013, 06:33 AM   #3
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Exposure issue

It is not a user problem, it is a technical problem.
I used the 'full frame, center-weighted' exposure type, and took photos of exactly the same subject.

Yves
02-14-2013, 07:01 AM   #4
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Yves, as far as I know, the K-x has a tendency to underexpose overall. Perhaps you can supply us with more details of the lenses you used, your testing methods and some sample shots with EXIF included, which might help us give a more informed and calculated response

02-14-2013, 01:07 PM   #5
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Exposure with Kx

I used a Tamron SP 17/3.5, a Pentax A135/2.8 and a Pentax A24/2.8.
Always at ISO 200, in 'A' - 'Center-weighted' exposure mode.
When going from 2.8 to 5.6, or from 5.6 to 11, the indicated shutter speed in the viewfinder was divided by 4 as it should be.
But my photos at 2.8 (or 3.5 with the Tamron) and at 11 are slightly underexposed (-1 IL?), and my photos at 5.6 slightly overexposed (+0.5 IL?)

Yves
02-14-2013, 11:34 PM   #6
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Yves, I see you have a K10D, I don't know if you have other lenses, but I assume you've tested the lenses on your other cameras to see if you can replicate the problem, but that it only happens with those three lenses on the K-x. I have a few lenses underexposing a bit more than others, but that is across the board, and when I use them, I automatically dial in the correct compensation when I start using it. As you experience the problem with three different lenses, one must assume it must be a fault with the camera, but there you've got me stumped. All I can suggest is that you do the usual, if you haven't yet, and that is to do a total reset of the camera to default settings, and give especially the lens contacts a thorough clean, and try again.
Perhaps some of the more knowledgable members have some other advice....
02-15-2013, 12:11 PM   #7
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Exposure with Kx

I don't have a K10D anymore...
But thanks for the suggestions, I will clean the contacts and reset my Kx.

Yves
02-15-2013, 03:01 PM   #8
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QuoteOriginally posted by altopiet Quote
Yves, as far as I know, the K-x has a tendency to underexpose overall.
My K-x has a strong tendency to overexpose. What I mean is that it will readily clip the highlights.

02-15-2013, 03:08 PM   #9
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I have a manual Kiron 28mm f2 that exposes well wide open, then gradually overexposes as I stop down. It's about a stop over by f8. I usually meter wide open, then count clicks for proper exposure.

I have a couple of A lenses. My Image (Cosina) A 28mm f2.8 acts the same way, it exposes properly wide open and overexposes gradually as I stop down. My other A lens, a Sears A 135mm 2.8 macro, exposes correctly at all apertures.

I don't blame any of this on the K-x, because all these lenses behave similarly with my K20D and K100D Super. Someone said the problem is that the mechanical apertures are not exact. So the camera takes a reading wide open, then adjusts for stops, but the lens openings are a bit off.
02-15-2013, 07:18 PM   #10
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Exposure with Kx

Sounds very similar to my problem. I wish so much that the aperture ring could be used on Pentax DSLRs, instead of being limited to the 'A' position.....
I suppose I will have to use bracketing or my brain (but I would prefer to 'focus' on geometry, composition and light), when time allows, to make well-exposed photos
02-15-2013, 09:49 PM   #11
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Used a K-X for two years and believe the aperture ring could be used on A type lens but not on M type in AV setting.No problem for me as I use manual most of the time.
02-15-2013, 10:29 PM   #12
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QuoteOriginally posted by Boker Quote
Used a K-X for two years and believe the aperture ring could be used on A type lens but not on M type in AV setting.No problem for me as I use manual most of the time.
That's partially correct. It's true that M lenses must be used in Manual Mode. In any other mode (Av, Tv, P, Sv) the aperture will not stop down, the photo will taken wide open.

With an A lens, you can use the aperture ring and the lens will behave like an M lens. But it makes no sense to use the aperture ring. Just set the ring to the A position and use the camera as you would any modern lens.
02-16-2013, 06:40 AM   #13
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Exposure Pentax Digital Camera

What I miss are my favorite modes with film cameras:
- Set the aperture on the lense, let the camera select the adequate speed (Av)
- Set the aperture on the lense and the shutter speed on the body, and tune the exposure (from -2 to 0 to +2 IL) using a graph in the viewfinder.

These procedures were simple, fast, and allowed full control of depth of field. Even 'K' and 'M' lenses could be used like this. But no 'modern' digital Pentax camera seems to match these procedures. And I suspect that exposure errors I noticed with the Kx would be less probable, electric connections being not used.

Yves

Last edited by Belgarchi; 02-16-2013 at 12:44 PM.
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