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Old Aug 5, 2011, 10:37 PM   #11
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Since I am not familiar with the model, I can only guess, but as I mentioned before, the calculated exposure and actual shutter speed can vary from what is displayed. Depending on how you have selected the increments in the menu, there could be 1/2 stop or greater difference. Does your camera allow you to set the increment in 1/3, 1/2, and full stop? How is it set? If, for example, you have set to full stop, the next increment down from 1/250 would be 1/125, so if the 1/250 was closer to the calculated value, it would be shown as the zero setting for exposure, even though 1/160 was the proper value.

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Old Aug 7, 2011, 3:33 PM   #12
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I think it is certain conditions that even though the exposure meter is at 0,
it may be just on the low or high side and that changes between the A and M modes.

The only time I see the difference is in matrix metering, this consistently has one stop difference between A and M where A always has the slower shutter speed. This has been done many times with a variety of scenes.

The EXIF says exactly what the camera says.
Here is the EXIF from a series of 4 shots of the same scene,

First two are matrix metering

Focal length: 200*mm*(equiv. 300*mm)
Aperture: F8
Exposure time: 1/200"
ISO speed rating: 320/26
Program: Manual
Metering Mode: Pattern


Focal length: 200*mm*(equiv. 300*mm)
Aperture: F8
Exposure time: 1/160"
ISO speed rating: 320/26
Program: Aperture priority
Metering Mode: Pattern

Next two are spot metering

Focal length: 200*mm*(equiv. 300*mm)
Aperture: F8
Exposure time: 1/250"
ISO speed rating: 320/26
Program: Manual
Metering Mode: Spot

Focal length: 200*mm*(equiv. 300*mm)
Aperture: F8
Exposure time: 1/250"
ISO speed rating: 320/26
Program: Aperture priority
Metering Mode: Spot

Spot metering is consistently the same with shutter speed.
Thanks for the extra thoughts on this, there must be an explanation.
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Old Aug 7, 2011, 3:55 PM   #13
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The difference between 1/200 and 1/160 is actually only 1/3 stop. (A stop is half as much, or twice as much light, and would be the difference between 1/200 and 1/100.) The amount of variation you're seeing could occur from an additional small cloud blocking the Sun. I don't think you're seeing any type of systematic error.
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