Should I bracket exposure with ISO or shutter speed on a digital camera?
Asked 11/29/2011
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On film, ISO was fixed, so exposure bracketing usually meant changing aperture or shutter speed. On a digital camera, if I want to keep aperture constant, what is the practical difference between bracketing with ISO versus changing shutter speed? Assuming depth of field should stay the same and motion blur is not a concern, is it generally better to keep ISO fixed and vary shutter speed, or does ISO bracketing give the same result?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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ISO Bracketing
This will create images with different amounts of noise in them. I call this grain, others just call it noise. Depending on the ISO range that you are using, you may or may not cause issues by doing this. Higher in the range, if you combine different areas of a ISO bracketed image you will see different noise profiles throughout and that may be undesirable.
Shutter Bracketing
This will give you images that are taken for different amounts of time. This could give you issues if you are concerned with speed because of movement in the image, such as if a car or person is in the shot. It also can cause issues if you are hand holding the camera. If the shutter speed becomes so slow that you introduce blur into the shot from your hand movements, then that would be a concern.
Recommedation
I wouldn't call one solution better or worse, it all depends on the situation and what your desired output is. If you are in a low ISO range already, bracketing will have few downsides. If you are in a fast shutter speed range already, bracketing will have few downsides. It is when you are in the upper limits of each that you have to chose what trade offs you are comfortable with.
Originally by user4892. Source · Licensed CC BY-SA 4.0
user4892
14y ago
0
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They are not exactly the same.
Changing shutter speed changes how long light hits the sensor. Changing ISO changes the sensor gain applied to that captured signal. In practice:
- ISO bracketing mainly changes the amount of visible noise. Higher ISO usually means more noise, and if you combine bracketed frames later you may end up with uneven noise across the image.
- Shutter-speed bracketing changes the exposure time, so it can introduce motion blur from subject movement or camera shake if the shutter gets too slow.
If motion blur and camera shake truly are not concerns, it is generally preferable to keep ISO constant and vary shutter speed, because that preserves a more consistent noise profile across the bracketed shots.
A special case: some digital cameras can create different ISO versions from a single capture by applying different sensor gains. That can be convenient because it avoids taking multiple frames, but the tradeoff is still that the higher-ISO versions will typically be noisier.
So: use shutter-speed bracketing when you want cleaner, more consistent files and can tolerate exposure-time changes; use ISO bracketing when keeping shutter/aperture fixed is more important.
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