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01-17-2010, 11:26 AM   #1
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KX indoor low light exposure differences w/ 2 lenses

Hi,
Below are a couple pics taken with my KX. The brighter using a Sigma 17-70mm f/2.8-4.5 and darker with a Sigma 10-20mm f/4-5.6. The pictures were taken in Program mode, AWB, auto ISO 200-3200, matrix metering, center focus, exposure not tied to focus point, no exposure compensation.

Why did the camera choose such a brighter exposure with the 17-70? It does not reproduce the actual scene. Further when shooting with the 17-70 the KX chose the widest aperture possible the exposure using the 10-20 is stopped down.

I've shot mostly with the 17-70 since getting the KX and the exposures the camera thinks is correct (whether program, Av, Tv, manual) seem to come out quite bright for indoor low light scenes.

Sigma 17-70: 19mm, f2.8, iso 3200, 0.5sec, program mode


Sigma 10-20: 20mm, f6.3, iso 3200, 0.25sec, program mode


01-17-2010, 11:36 AM   #2
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The 17-70 exposure looks correct. When set to any auto exposure line the camera should expose so that the sensor receives the same amount of light regardless of the light level of the subject. So, a dim room will appear in the picture to have the same amount of light as a bright room. The camera shouldn't under expose automatically to make the dim room look dim. The camera is not exposing correctly with the 10-20 since it is underexposing.

I don't have either lens, but maybe someone else can explain why 10-20 is underexposing?
01-19-2010, 10:25 PM   #3
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QuoteOriginally posted by mgoblue Quote
The 17-70 exposure looks correct. When set to any auto exposure line the camera should expose so that the sensor receives the same amount of light regardless of the light level of the subject. So, a dim room will appear in the picture to have the same amount of light as a bright room. The camera shouldn't under expose automatically to make the dim room look dim. The camera is not exposing correctly with the 10-20 since it is underexposing.

I don't have either lens, but maybe someone else can explain why 10-20 is underexposing?
Hi mgoblue,
Thanks... on dpreview GordonBGood (with details of calculating LV) and Marc S pointed out the 17-70 had just enough light to meter correctly (and capture an unrealistically bright picture) and the 10-20 did not.
KX indoor low light exposure differences w/ 2 lenses: Pentax SLR Talk Forum: Digital Photography Review

Then how do I adjust the exposure so I capture a realistic image with the 17-70?
01-20-2010, 01:10 AM   #4
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That is what "exposure compensation" is for, dial in -1 (for example) if you want a darker picture, or +1 if you want it brighter.

01-20-2010, 06:11 AM   #5
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I noticed a slight difference (maybe 1/3 stop) between exposure with the DA 40 ltd and the FA 35/2 at ISO 3200 as well. It was not nearly as dramatic as the results from the OP, though.
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