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Comment by esteth | Hacker News Reader

stops only need to be adjusted for total photons gathered, not for photons per unit square

Yes, and a much smaller sensor will of course gather much less light.

For the same aperture, sure. But you are not going to be shooting macro photos at f1.5 on full frame (for depth of field reasons alone). For real world macro photography you'd typically be stopping down at least to f8 on a full frame camera. At that point the DSLR has a considerably smaller advantage in terms of the total amount of light gathered.

One thing that people often miss is that you can think about all of this just in terms of the absolute diameter of the aperture (not the f number, just the diameter in mm). For a given angle of view, the diameter of the aperture determines how much light you gather. The question is simply whether a photographer using a DSLR is going to be able to use an aperture that is significantly wider (in mm) than the ~4mm aperture of a phone camera. For depth of field reasons, it's unlikely that they will be able to do so.

Why wouldn’t you need to stop down similarly on a phone camera?

Because depth of field depends on focal length as well as f number. Or to put it another way, it depends on the absolute diameter of the aperture, not the ratio of the focal length to the aperture diameter (= the f number).

(Also, of course, you can't stop down on a phone camera as it has a fixed aperture.)

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