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11-27-2009, 08:06 AM   #1
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K7 Exposure...

To all and especially Falk

Have you noticed an exposure difference between the k7 and other cameras?
There is a thread on DP which indicates that the k7, at a given ISO, will require 1/2 stop more light.

I have run tests comparing my k10 to the k7 in a controlled environment and have noticed this as well. Gordon Good, EE extrondinaire, seems to think that the K7 exposes to the right to make up for black read noise. Much of this discussion is captured in the thread below. My moniker in that forum is Yesman.

K-x vs K-7, without K-7 ISO cheating: Pentax SLR Talk Forum: Digital Photography Review

To me, what matters is that I am able to capture an image with a given fstop and shutter speed which results in a image with good quality wrt to noise et al.

Thus if the k7 requires more ligh to achieve this objective, it is not desirable and effectively derates the ISO. However, I have often had to dial in +EV compensation on the K10 so I am not sure yet if the issue is the difference in metering or the effective ISO of the K7.

Thoughts:?


Last edited by spartan; 11-29-2009 at 07:20 PM.
11-29-2009, 07:21 PM   #2
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Bump....has anyone measured the exposure differences between the K7 and other cameras
11-29-2009, 08:02 PM   #3
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The K7 exposes more accurately than any Pentax DSLR before it. A half stop is SFA in the real world. Go and take some pictures and stop worrying about trivialities.
11-30-2009, 02:36 AM   #4
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Wouldn't this also depend on lens used ? I recall vividly when i tested my Sigma 18-50mm macro 2.8 vs Tamron 17-50mm 2.8 lens, the Sigma always gave me more overall light and working faster shutter speeds at the same iso/aperture, than my Tamron. For that reason I chose my Sigma for indoor low light shots more than my Tamron.

11-30-2009, 03:25 AM   #5
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QuoteOriginally posted by eva2000 Quote
Wouldn't this also depend on lens used ? I recall vividly when i tested my Sigma 18-50mm macro 2.8 vs Tamron 17-50mm 2.8 lens, the Sigma always gave me more overall light and working faster shutter speeds at the same iso/aperture, than my Tamron. For that reason I chose my Sigma for indoor low light shots more than my Tamron.
I've did some quick tests with my K7 Tamron 17-50 2.8 vs my K100D with the 18-55 kit lens, and when using the same apertures and iso, the K100D always gave me a faster shutter speeds and sharper pictures in low light situations.

I have yet to test the two bodies with the same lens.
11-30-2009, 05:30 AM   #6
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Hi Eva2000 and mindglow

In both cases I used a 50mm A series lens opened to 1.7 to ensure that the lens was not the determining factor.
11-30-2009, 05:45 AM   #7
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QuoteOriginally posted by spartan Quote
Hi Eva2000 and mindglow
In both cases I used a 50mm A series lens opened to 1.7 to ensure that the lens was not the determining factor.
If you check the histogram and find the K-7 histogram shifted to the right by half a stop, then it is fine. If the histograms look identical (not the shape, but the horizontal position), then the K-7 is indeed gathering less light.

This is not perfect, but is a bit better than just going by the readings alone.
11-30-2009, 07:17 AM   #8
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QuoteOriginally posted by spartan Quote
Hi Eva2000 and mindglow
In both cases I used a 50mm A series lens opened to 1.7 to ensure that the lens was not the determining factor.
Have you tried this at low iso's?
I'd be interested in the results here and w/ a lens other than the 50 because anomolies do show up at wide open w/ these lenses (fast lenses).
Soooo just reproduce this at say iso 200 and an f4 lens....


12-02-2009, 07:42 PM   #9
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Yes those are my tests of K10 and K7 under same lighting conditions converted with RawT. set to neutral

Nick
12-02-2009, 07:53 PM   #10
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Gordon B Good says that the K7 over exposes and then decreases by a little over half a stop to decrease dark read noise (this is apparently automatic with ACR). Certainly seems like he knows what he is talking about, but it is over my head. I guess if you want to, you can shoot manual and force whatever shutter speed, iso and aperture you want to. It would probably look about the same, but with more noise in the shadows.
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