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Let's say that you're in a very controlled environment, there is no hurry to get the shot, and you're shooting manual.

In order to correctly expose the photo, what order should you alter the ISO (if shooting digital), shutter speed and aperture; and why?

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It depends on where your camera is set when you start and what you want the photograph to look like when you are done. There is no right or wrong answer to this question. –  Michael Clark May 2 '13 at 14:55
    
I am not sure this question is a good fit. There is no way to correctly set exposure...as the answers indicate, what you change really depends on what you are photographing and what your goals are. There is no correct answer here, and any answers that try to be "correct" will only mislead you. –  jrista May 3 '13 at 2:47
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marked as duplicate by mattdm, MikeW, AJ Henderson, Paul Cezanne, Caleb Dec 27 '13 at 5:15

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.

4 Answers

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It, of course, depends. You want to change that which affects the photograph negatively the least.

If you are shooting scenery, you have a decent latitude in terms of aperture. You ideally want to be above f/8 and can easily go as far as f/22 (although you may lose sharpness after f/16). You have even greater latitude in terms of shutter speed, anywhere from 1/15 with a tripod (or less!) to 1/5000 (although if it's a sunny day you'll probably be closer to the faster end of the spectrum).

ISO can vary anywhere from ISO100 to 800 (or even higher with newer cameras). You will notice noise less in brighter scenes than darker.

Before you can decide what to change, you need to decide what is important. I am assuming you are not using a flash, because that will dictate your choices for you to a greater degree. So what is important?

Are you trying to freeze something moving, such as a bird, or are you trying to give water that flowing texture? If so, you will want to fix your shutter speed at something appropriate, 1/500 for moving animals (or faster) and 1/15 or less for water. If it's just pastures and mountains, then it really doesn't matter since nothing around you is moving.

Are you trying to capture something up close and personal, or do you want sharpness throughout the frame? If it's a macro of a flower, you will want to increase your aperture as much as possible, ideally hitting f/1.8 or 2.8 depending on your lens. If it's a scene you're after, then get up to f/11 or higher. Use the depth indicator if you have one.

Once you have those dialed in, you mess around with the other two within the constraints of your scene.

Is it dark, moody, and moonlit? You will want to set your ISO to around 400, and see where your shutter speed ends up. Do you not have a tripod? Then set the shutter speed to the inverse of your focal range. A 50mm lens should be fine hand-held at 1/50 s. Now adjust your ISO again until your exposure is right. Or, have fun, and set it until it's wrong :)

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You had me at "it depends"... lol. Optimize for what's most important, though, makes sense. –  D. Lambert May 2 '13 at 16:06
    
Depending on the camera (this is the case for my D800) diffraction can start to degrade sharpness above f/8. –  daalbert May 2 '13 at 20:29
    
You're correct, theoretical sharpness usually drops at f/8 for most modern DSLRs but I personally have difficulty seeing a difference in sharpness until hitting f/16. Of course, I limit the discussion to normal photography, where you are usually sharing photos to view online or printing them out usually no larger than 5x7. If you zoom to 100% and crop to the edges, you can detect some loss of sharpness at the theoretical level. –  multiphrenic May 2 '13 at 22:50
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In perfect conditions, if you could stop time, the best will probably be:

the lowest native ISO of your camera (not counting the low 1 or similar ISOs of the different brands),

the f-number in the sweet stop of your lens, usually around two f-tops smaller of the widest you have,

and choosing your speed and/or the power of your light sources consequently.

Other things you should take into account are:

the depth of field you want, which you can be modified with your f-stop or tilting the lens (if possible), but try not going further than f16 because of driffaction,

the speed you need for freezing movement (or not freezing it, depending the effect you want). Here the best you can do is trying first with the shutter speed and the T1 of your flashes (the duration of the pulse of light) and if need then go with the ISO.

Hope this helps!

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There order does not matter if you are in Manual mode. The picture just requires all three to be set. Actually, they are always all set since exposure parameters have no unset value. If you are shooting manual it is your responsibility to set parameters to get the exposure you want but the order in which you set parameters has no impact on the outcome.

Personally I would set the most obvious ones first. This is usually is Aperture to get the desired depth-of-field. Then I set the lowest ISO if using a tripod or the lowest one which would allow me to use a reasonable shutter-speed if not using a tripod. Then shutter-speed is set last in this case. It is easy to imagine cases where I would set shutter-speed first, such as when doing portraits when I know I need a certain speed to freeze the subject.

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There isn't really an optimal choice. In general, you will almost always want the lowest ISO possible to reduce noise. You then want to adjust the shutter to be as fast as necessary to capture any movement and then want to adjust the aperture for the desired depth of field.

If the image is too bright, you can speed the shutter. If the image is too dark, you can raise the ISO. You can also choose to compromise on either shutter or aperture if keeping low noise is more important to you than a little motion blur or a slightly different DoF than you wanted.

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