Why do full-frame and crop cameras need the same ISO for the same shutter speed and aperture?
Asked 1/6/2019
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2 answers
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I shoot handheld wildlife with a Nikon D500 and a Nikon Z6, using a Sigma 150-600mm Sport. I expected the full-frame Z6 to let me use a lower ISO than the crop D500 for the same shutter speed, since the larger sensor gathers more total light. But in testing, both cameras needed essentially the same exposure settings.
For example, at 600mm and f/8, if the D500 needed ISO 640 for about 1/5000 sec, the Z6 also needed about ISO 640 for the same shutter speed. However, the Z6 files looked noticeably cleaner at the same ISO.
Why is the exposure the same on both cameras if the full-frame sensor is larger? And does full frame let me safely use slower shutter speeds for handheld wildlife, or is the main benefit just lower noise at the same exposure?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
6
A full frame sensor gathers more light for the total area, but that's because there is more total area. The light gathered for the same sized portion of the recording medium is the same for any combination of f-stop and shutter speed — no matter the total size.
This means that if you are getting the exposure you want with f/8 and ¹⁄₅₀₀₀th at ISO 640 on one camera, you'll get (approximately, give or take minor differences between the setups) the same exposure on any other camera regardless of shutter speed.
However, you noticed something important:
One difference I noticed immediately is that the full frame image has significantly less noise even though the ISO is the same.
This is the advantage of the larger sensor. So, you can use higher ISO, which will let you use faster shutter speeds.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
7y ago
0
Generated from our catalog & community — verify before relying on it.
For the same scene brightness, aperture, and shutter speed, exposure is essentially the same on crop and full-frame cameras. A larger sensor gathers more total light only because it has more area, but f-number already accounts for light per unit area, so you do not automatically get a faster shutter speed or lower ISO just from using full frame.
What full frame often gives you is cleaner image quality at the same ISO and exposure. That matches what you saw: the Z6 needed similar settings, but produced less noise.
So the practical advantage is not “same ISO but faster shutter” — it’s that you can usually push ISO higher with less noise, or enjoy cleaner files at the same ISO.
Full frame also does not inherently reduce subject motion blur. If the owl moves, you still need the shutter speed required to freeze that motion. Handheld shake is a separate issue, but with long wildlife lenses, subject motion is often the bigger limit anyway.
In short: same exposure settings, cleaner full-frame files, and more usable high ISO — but not automatically slower safe shutter speeds for moving wildlife.
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