Q: do i have 2 buy a sd card for the r4 or can i use my camera sd card???
A: There are 3 different size SD cards, regular, mini and micro. Your camera most likely uses a regular SD card--you need the micro SD card for the R4, and no, they are not interchangeable. The micro cards are tiny, 4 of them would fit on a postage stamp. The most common use for a micro SD card is in a cell phone, most cameras though take the regular size. So yes, you most likely will have to buy a micro SD card for your R4 if you don't already have one.