Tuesday 6 March 2018

file size - Why is the amount of photos that fit on one card dependent on ISO?


I have a Canon 550D with a 16GB SD card. I noticed that, when in P-mode, if I choose an ISO of 100 I can shoot 595 raw files on an empty card. If I choose an ISO of 200 this is 590. And if I choose 400 this number decreases to 583. Here below is the rest of the ISO vs. space



ISO __ | __ Amount of raw files that fit on 16GB
800 __ | __ 569
1600 _ | __ 556
3200 _ | __ 539
6400 _ | __ 510
12800_| __ 477




Does anybody know, why the filesize of one raw photo increases with the ISO?



Answer



In general, photos at lower ISOs will have less noise. This means that they compress better (remember that RAW files have lossless compression) and so, on average, you'll be able to fit more images onto the card.


The other important thing to remember is that the number shown is only an estimate - how many images actually fit depends on what you take photos of and how much they compress.


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