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I have a Canon 60D. I've had it for a month now. Today while taking pictures I noticed that if I take a picture in AV Priority, the shutter speed is really slow. So I took a picture in Auto and noted the shutter speed ( 1/60 ), ISO ( 400 ), and aperture ( 4.0 ). Then I switched to AV and on the same shot set my aperture to 4.0 and the ISO was on 400, but the shutter speed was set to 1/6 not 1/60. I uploaded the raws to my computer and reviewed the settings and it seems everything else is the same. Just trying to find a reason for this. My assumption is that the settings to get the proper exposure between modes shouldn't matter - at least between AV and auto - when taking the same shot. I also noticed that something is different in the shot - perhaps the white balance, but that is set on auto as well. Thanks.

So I tried again comparing P and Av. I had similar results. I'm on my phone, so these images are from the info screen on the camera.

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up vote 3 down vote accepted

It would be easier to compare Program versus Aperture priority because Auto ignores a lot of other settings, most importantly Exposure-Compensation and choice of metering patterns. The ignored settings depends on the camera and I do not have a 60D on hand to check.

Had you changed any of these settings on your camera you would have a large discrepancy. The other thing is that flash works differently in Auto on plenty of cameras. This may enforce a minimal shutter-speed like 1/60s and ask the flash to fire. While in A mode, the flash wont fire unless the right Flash-mode is set and therefore a lower shutter-speed is required.

To find out what is the case in your setup, do the same comparison between P and A. If those coincide, then you have to try different settings to see which one is ignored in Auto mode.

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Thanks for the info. I compared all the other setting such as flash, exposure compensation, and metering. I sent the same question to Canon and all they said was I could send it in if I wanted. I will try what you said with P mode. I also reviewed the settings in the RAW. Thanks again. –  Brian Feb 15 '13 at 1:27
    
Please see my edit. –  Brian Feb 15 '13 at 2:36
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@Brian - Puzzling! Did the flash fire in either case? If so, what flash mode is set? Clearly Av is over-exposing and the AWB has not chosen the same color-temperature for both images. One more thing since metering is linked to the AF-mount sometimes, make sure the same focus-point is used (or use MF) to isolate the issue. –  Itai Feb 15 '13 at 2:58
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Yes. That is why I was asking about the flash. In A mode, the scene is exposed assuming no flash and then flash is added which is why you have an over-exposed scene. This is what is called Fill flash and is used to fill out shadows for a bright scene. As I said, the exact behavior depends on the camera. –  Itai Feb 15 '13 at 3:27
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Yes, it has to be because of the flash. With flash on with auto settings, camera sets 1/60th of a second and sets flash output based on the exposure required. That's why setting exposure compensation is not changing shutter speed, only flash output. –  Evaldas Dzimanavicius Feb 15 '13 at 7:55
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