Alley in Pisa, Italy

by Lars Kotthoff

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I've heard that aperture can change the exposure, but I would like to know if this is true, and how it does it.

P.S. I hope this question isn't dumb like my last two.

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marked as duplicate by drfrogsplat, mattdm, MikeW, AJ Henderson, John Cavan Mar 26 at 2:25

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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I don't think your questions are dumb. Sometimes it's unclear what direction you're coming at them from, though. It would be helpful if you could explain what you don't understand from existing Q&A like What is aperture, and how does it affect my photographs? or What does f-stop mean? –  mattdm Mar 30 '12 at 23:25
    
I found those questions by looking at aperture and clicking the word "faq" at the top of the results (not the faq link at the very top of the page). –  mattdm Mar 30 '12 at 23:27
    
A good experiment: take a picture in full auto (no flash). Write down the ISO, Av, and Tv settings. Switch to Manual and set those 3 settings. Now take more pictures, changing just the aperture between pictures. Look at the results. Does that help? Then build the rotary version in uscoles.com/exposures.pdf (from the bottom of the page linked to from the comment to the second question mattdm just posted) and repeat the experiment, changing both aperture and shutter speed according to that tool. Does that help? –  drewbenn Mar 31 '12 at 5:31
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I recommend you to read this question and the answer by @mattdm photo.stackexchange.com/questions/6598/… –  akram Apr 2 '12 at 19:50

1 Answer 1

up vote 5 down vote accepted

It depends on your definition of exposure. Exposure is the overall amount of light that falls on the film or sensor. So by that definition, if you have a fixed shutter speed, then if you use a wider aperture, you'll let in more light, so you will increase the exposure. A narrower aperture opening will let in less light, so less exposure.

Keep in mind that a camera on Auto mode will adjust, so if you narrow the aperture, the camera will slow the shutter to compensate, and you'll end up with roughly the same exposure. So for aperture to affect exposure, you have to keep other parameters constant.

People also use the term exposure as a substitute for shutter speed, as in "I took a long exposure of the stars". If you are thinking exposure = shutter speed, then I can understand your confusion. But the real definition of exposure is the overall amount of light. This is affected by the exposure triangle of ISO, aperture and shutter speed.

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