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06-18-2012, 08:17 PM   #1
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K7 exposure problem

Can anybody help or have experienced a problem with their K7 camera being roughly two F-stops lower than the subject light exposure. I have tried my camera and lens combination against a friends camera at same facal length, aperture, shutter speed and ISO settings and my camera is roughly 2 F-stops lower.

eg example: Shooting at same subject and lighting
My camera K7 at 50mm required F3.5 @ 1/8 100ISO, while friends camera at 50mm required F3.5 @ 1/15 100ISO

Camera details
K7 with Sigma 17-50 F2.8
Cannon 7D, 18-200 F3.5/F5.6

My photo's come out correctly exposed, its just that I required a larger F-stop setting or slower shutter speed for the same subject. Was wondering if this could be a setting issue, lens issue, CMOS sensor issue or light metering issue?

Any suggestion as to what I can do to fix or should I look to get rid of camera and lens?

06-18-2012, 10:15 PM   #2
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Check your metering mode. Is it spot, center weight or matrix? Also a sample photo would help us identifying the problem.
06-18-2012, 10:16 PM   #3
dms
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A different lens (at same indicated f number), sensor (actual iso at same indicated iso), or light meter (external or internal), internal software conversion (to jpg) etc. will not be be the same. The important thing is it's getting proper exposure, and if not one biases with a +/- ev value. Also the example you give (1/8 versus 1/15 sec) is 1 stop difference, which is not that big a difference. This kind of variation was very common when dealing with film, and would still be present in digital.
06-18-2012, 11:30 PM   #4
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Sorry, but what makes the Canon right but the Pentax wrong exposure?

Anyway, aperture is not directly equal to transmission. Look up t-stops.

06-19-2012, 08:55 AM   #5
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I use K7 with no problems,
please upload few photos so we could get an idea of your issu
06-19-2012, 09:02 AM   #6
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QuoteOriginally posted by calsan Quote
Sorry, but what makes the Canon right but the Pentax wrong exposure?

Anyway, aperture is not directly equal to transmission. Look up t-stops.

Agreed, in fact i find many out of the camera shots metered over exposed on Canon (and a tad garish on the colour for my taste)
And as pointed out this is a 1 stop variance. not a big deal. in fact there is no such thing as the one perfect exposure in any case. It's an area your camera can only guess at what you actually want.
if you haven't already read the book below, it will give you a better understanding of how to expose

Understanding Exposure, 3rd Edition: How to Shoot Great Photographs with Any Camera: Amazon.ca: Bryan Peterson: Books
06-19-2012, 10:21 PM   #7
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Original Poster
Thanks for the feedback guys,
I know its very subjective, but my K7 indicates that I need to use flash for indoor shots that other camera's/ lens combo with same apperiture can take proprely exposed photo. I have to constantly run lower shutter speeds and get blurred movement shops that other camera's can take with same apperiture and faster shutter speed. My only alternitive is to up the ISO to 200, 400 or 800.
I'm going to check it against another pentax with same lens and see if my camera still functions at lower shutter speed and larger apperiture for same photo/ light senariors? Another thought is possible white balance issue but if both camera's are set the same I should be able to eliminate this.
I can't see anyone else with simular issues on the troubleshooting forum so I hope it's just operator error.
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