Does a larger sensor make the image brighter at the same field of view and f-number?
Asked 7/6/2015
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If two cameras have different sensor sizes but are set up to give the same angle of view, and both lenses are set to the same f-number, will the larger sensor produce a brighter image? For example, compare a 1/3-inch sensor and a 1-inch sensor, both with 1 MP resolution, both using lenses matched to the sensor format, both around 100° field of view, and both at f/2.0. If the smaller-sensor camera looks dark indoors at 100 fps, would the larger-sensor camera look brighter? If not, how would you determine what f-number on the larger format would match the image brightness of the smaller one?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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The image brightness will be the same. The entrance pupil size does not matter for image brightness - what matters is only the F number (or more accurately, T number which is equal to the true f number divided by the square root of the transmission.)
In a bit more detail:
If you fix your field of view at 100deg and vary the sensor size, the focal length scales between different image sizes, as does the entrance pupil diameter. Since the focal length directly affects magnification and shorter focal lengths provide greater magnification in image space (that is, behind the lens) the sensor sees a much bigger pupil for a 10mm f/2.8 lens than it does a 20mm f/2.8 lens.
Originally by user40937. Source · Licensed CC BY-SA 4.0
user40937
11y ago
0
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For image brightness on the sensor, sensor size by itself does not matter. If both cameras have the same field of view and the lenses are set to the same f-number, the illuminance at the sensor is essentially the same, so the image brightness per unit area is the same.
Why: f-number already accounts for the relationship between focal length and entrance pupil diameter. With a larger sensor, you use a longer focal length to keep the same angle of view, and the entrance pupil grows proportionally. Those changes cancel out in terms of image illuminance.
More precisely, transmission is best described by T-stop, but if both lenses are truly the same f-number and similar in transmission, brightness will match.
So a 1-inch sensor at f/2.0 will not be inherently brighter than a 1/3-inch sensor at f/2.0 just because the sensor is larger. To match brightness, use the same f-number (or, more accurately, the same T-stop) and the same exposure time.
A larger sensor can still collect more total light overall because it has more area, but that does not make the image itself brighter per unit area.
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