I am using 32Gb cards in my D7200 set one to NEF and two to JPEG. The "shots left" display shows 589 on a new card and I am trying to calculate why. Can someone help me with my sums / tell me where I have made a wrong assumption?
To start, the raw image will be 24MP - so 24,000,000 pixels
NEF encodes each pixel as 14 bits - so picture will be 336,000,000 bits
8 bits in a byte - so each picture will be 42,000,000 bytes
Using the salesman's Mb(1), each picture is thus 42Mb
32 Gb SD card = 32,000Mb - so should hold 32,000/42 = 762 photos. 25% more than 589.
So where have I gone wrong?
Looking at the NEF files on a PC I see they are between 29Mb and 33Mb - so less than 42 - so I would expect to fit even more on the SD Card.
Also, why are NEF files different sizes? Is there some optimisation taking place with them too?
(1) salesman's Mb = 1,000,000 bytes rather than 1,048,576 - used to make smaller disks seem bigger on the box label!