Why does a light meter sometimes give an aperture reading instead of a shutter speed?
Asked 9/24/2014
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2 answers
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I understand the exposure triangle and usually choose aperture myself based on depth of field, then adjust shutter speed or ISO for exposure. But in some portrait and flash-lighting examples, photographers say the light meter told them to use something like f/10 or f/16. That feels backwards to me.
Why would a meter be used this way? In portrait situations, especially, it seems more natural to pick the aperture you want and let shutter speed follow. Is this mainly something that happens with flash or studio lighting, where shutter speed is limited by sync speed or doesn’t affect the flash exposure the same way?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
6
When we talk about flash photography; this is because the shutter speed does not contribute to the exposure from the flash. A flash will output a burst which last maybe 1/1000s, so changing the shutter speed won't affect the exposure from the flash but form the other continuous light sources.
And since the light meter used in the first video you linked seems to be connected to the flashes, it tells him what aperture to use to get a correct exposure from the flash.
Originally by user26915. Source · Licensed CC BY-SA 4.0
user26915
11y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this is mainly a flash/studio-lighting workflow issue.
With flash, shutter speed usually has little or no effect on the flash exposure, because the flash burst is much shorter than the shutter time. Shutter speed mainly affects ambient light, and in many studio setups it is fixed near the camera’s flash sync speed. ISO may also be fixed for image-quality reasons. Once ISO and shutter are fixed, the remaining exposure variable is aperture, so the meter reports the f-stop that matches the current flash power.
In that sense, the meter isn’t really “choosing” creatively for the photographer—it’s telling you what aperture the current lighting setup supports.
You can still work the other way around: pick the aperture you want for depth of field, then change flash power, light distance, ISO, or ambient/shutter settings until the meter reading matches your chosen aperture.
So both approaches are valid:
- fixed lighting -> meter suggests aperture
- fixed aperture/creative intent -> adjust lighting to match
In high-speed sync situations, choosing a wide aperture may force a very fast shutter speed, which is why HSS comes into play.
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AI11y ago
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