Why use aperture priority vs shutter priority if they can produce the same exposure?
Asked 3/29/2013
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In a static scene with fixed light and ISO, my EOS film SLRs often give the same aperture/shutter combination whether I use aperture priority (Av) or shutter priority (Tv). For example, if Av at f/8 meters 1/250s, then in Tv at 1/250s it meters f/8. If the camera is just choosing the other variable to reach the same metered exposure, what is the practical difference between Av and Tv? Is the difference simply which setting I want to control for creative reasons, and is Program Shift basically similar in that sense?
Originally by user19032. Source · Licensed CC BY-SA 4.0
user19032
13y ago
2 Answers
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They allow you to make different creative decisions. Take Av (aperture mode), if you are creating a portrait, you will likely want a large aperture for a flattering shallow depth of field, so maybe you set it to f2.8 and let the camera figure out the best shutter speed.
However, if you want to create a landscape, you want most of the image in focus, so you choose f11, and again let the camera choose the best shutter speed.
If however, you are shooting a sports scene, shutter speed becomes critical so you switch to Tv (time value) mode and set your shutter to 1/250, letting the camera choose the smallest aperture possible. In bright light that might be f5.6, but in low like it might be f2.8.
On the other hand, if you want to take a creative shot of dancers where you want to create some motion blur, you might choose 1/15.
It all depends on what your creative goal is, balanced with the lighting conditions you are faced with. In certain conditions both modes may produce similar or identical exposure values (like low-light shooting where your aperture will usually be wide open, no matter what), but you get to decide whats important.
Originally by user8843. Source · Licensed CC BY-SA 4.0
user8843
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes: for the same scene, ISO, and metering, Av and Tv often arrive at the same exposure because shutter speed and aperture trade off against each other.
The real difference is which variable you choose to lock in:
- Av when aperture is your priority, usually to control depth of field. Example: wide aperture for blurred backgrounds in portraits, or smaller aperture for more of a landscape in focus.
- Tv when shutter speed is your priority, usually to control motion. Example: fast shutter to freeze sports, or slower shutter to blur movement.
So they are not different metering systems; they are different ways of telling the camera what matters most for that shot. In a static tripod test, they can look interchangeable because neither motion blur nor depth-of-field changes are forcing a different choice.
Program and Program Shift are similar in that the camera still aims for the same metered exposure, but they differ in how much direct control you assert over aperture or shutter speed.
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AI13y ago
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