Picture capacity

Dont know if I am being an idiot and missing something. Only if I set my 5D mk3 to auto ISO I get 185 shots with my particular cards. If I set any other ISo ie 100 200 or even 6400 the counter shows 232on the frame counter?

Any thoughts?

Hard to say what logic Canon follows - but a photo does not have a fixed size, so Canon have to make use of some average size to give an approximate count of number of photos that fits.

With low ISO, the sensor can produce lots of bits of data.
With high ISO, there will be much noise.
But what you shoot will also greatly affect how large the files will be, i.e. amount of noise/features to capture.

So it is reasonable that the guestimation shown by Canon will vary depending on your ISO settings. In the end, neither value will be correct. Just better or worse guesses.

Thanks pwm2. Makes sense!

Appreciated!

hmm, that number should go down as ISO goes up. Increased ISO adds to file size. For example, the 5D3 sensor produces ~22MB @ 100 ISO, but crank the ISO up and you can get a 30MB+ image.

Even with RAW the file is compressed, although in the case of a RAW losslesy. Anything that makes compressing the file harder, be that high ISO noise, or just an image with lots of very fine detail in will make the file size bigger. In the case of ISO noise Canon have a very good idea how that will affect the file size, hence the changes in the estimate of number of shots left.

Alan