I am thinking about acquiring a 64GB iPad mini and other than its other purposes, use it for back up for RAW captures on my Nikon D80 while on vacation. I'm wondering approximately how many RAW files I can expect to fit on the device.
Suppose you want to dedicate 50gb to photos. (50gb * 1024 mb/gb)/SIZE_OF_PHOTO, for my d7000 I get a result of about 2k photos.
The 'easy' way is to just select a chunk of your image library, find the size and then see how many pictures it is. If you want more space used, select more pictures from the library.
Divide the amount of free space on your iPad mini (x) by the size of each RAW image (y).
The number of RAW images you can fit on the device (b) is:
So if you have 50,000MB of space on your iPad and your RAW files are 12MB, then the number you can fit is 50,000 divided by 12, which is 4,166. However, you'll need to replace 50,000 and 12 with the actual space on your iPad and the actual size of your RAW images (which varies according to camera model) and then do the calculation yourself.
You would need to factor in how much space you would use for other things on the Mini. My 32GB iPad has about 28GB usable, so I'd expect that you would see about 56GB usable. Subtract how much room you need for music, ebooks, apps, etc. I'd guess that you could probably count on 32GB of pictures, maybe as high as 48GB. Look at the SD cards you use, and extrapolate. If you currently can put X RAW files on an 8GB SD card, expect 4X to fit in 32GB or 6X in 48GB. That should get you in the ballpark.