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02-27-2010, 03:33 PM   #1
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Exposure Pentax K7 and Sigma DC 18-50 f2,8

Hi,

the mentioned lens at the K7 shows underexposure of 2/3 stop over the whole range of aperture.

I just recently bought both and most of the shots were too dark/ resp. I had to push the exposure almost with every foto, so I started some tests:
I took several test shots of a standard grey (different apperture, different focal length) and to get the peak in the histogram in the middel I have to push exposure by 2/3 stop. I compared it with my MF Pentax 1:1,4/50mm and things are fine with that lens - so it's probably the Sigma lens.
Of course this is something for the foto shop, but I just wonder if anybody else had this effect?

Ulrich

02-27-2010, 03:42 PM   #2
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I have had and used this lens myself (I actually have it listed for sale now here in the marketplace forum). I didn't ever have any exposure problems with it on my K10D and K20D bodies.

I did once have intermittent metering problems with a Sigma 28 f/1.7. Sent it back to Sigma, they fixed it, and today it's one of my favorite lenses. Perhaps your 18-50 has a problem. Have you called Sigma?

Will
02-27-2010, 04:56 PM   #3
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Thank you for your quick reply! Not yet contacted Sigma, I wil do in the next days and post the outcome. Good to know that it's not a general 18-50 Problem, so probably my one can be fixed.
Ulrich
03-01-2010, 09:06 AM   #4
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QuoteOriginally posted by ulrich Quote
I took several test shots of a standard grey (different apperture, different focal length) and to get the peak in the histogram in the middel I have to push exposure by 2/3 stop.
In that case it's more like 1/3 a stop or less underexposed, because "correct" exposure of a gray card should yield about 1/3 to 1/2 stop left of center on a histogram on an properly calibrated (according to ISO standards) meter.

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