Help with NEF

niemeyjt

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?

Thanks,

Julian

(1) salesman's Mb = 1,000,000 bytes rather than 1,048,576 - used to make smaller disks seem bigger on the box label!

Ironheart

The counter is highly conservative, based on worst case with a head-wind. Files are lossless-ly compressed, so a picture with a lens cap on will be smaller than a field of daisies. You will be able to squeeze more files onto a card, YMMV.

heartyfisher

The space on the card is not like a bucket of water, more like a bucket of bricks. so the volume of the content is never as much as the total volume of the bucket.

paulr

Good analogy Heartyfisher