Nikon's Mysterious r00 Error and Other "r" Numbers
Modern digital cameras are complicated pieces of equipment. New users in particular can have a hard time making sense out the various messages their camera's LCD panels and viewfinder convey. If you're a Nikon shooter, you've probably noticed the mysterious "r00" other "r" numbers when you press down on the shutter release. Here's the scoop on what they mean.
When you take a picture with your camera, the final result ends up on your compact flash or SD card, but it doesn't get there right away. Temporarily, it lives in a buffer memory area in your camera. Nikon made it work this way since it takes far less time to write to the buffer than it does to the storage card. Think of it in much the same way as the relationship between the memory and the hard drive in your computer. One is just a lot faster than the other. By temporarily buffering images in the camera's memory, you can keep shooting even if the image you just shot hasn't had time to make it all the way to the storage card.
But there are limits. As camera resolutions go up so do file sizes, and fast buffer memory isn't cheap. Different camera models have space for different numbers of images in their buffer, but with a fast enough shutter speed you can fill up even the biggest. The "r" number that you seen when the shutter release is partially depressed is an attempt to show you how many shots remaining you have room for in the buffer. The "r" stands for "remaining."
Depending on whether you are shooting raw or jpeg, the count will start out at a different number and count down as you shoot. Pause for a while so your storage card can catch up a bit and the count will start to go back up. If you get down to r00 you can't shoot any more unless do wait a bit. This is the point at which at least some users notice the "r" number for the first time. Their camera locks up and they have to figure out what is going on. The fiddle with things a bit and then it starts working again. Of course they didn't really fix anything; the camera simply offloaded some of the buffered images to make more room available. Understanding what happened isn't entirely obvious since the "r" number doesn't show unless you press the shutter release. As you might guess, the details are in the manual, but few users read the whole thing. If you missed this, don't worry. It's a frequent question from new users.
The "r" number will also vary based on current image quality settings such as whether you are shooting jpeg fine or jpeg basic, 12-bit RAW versus 14-bit RAW, and so on. This stands to reason since the space needed for each varies. The number also changes based on whether you have the Long Exposure Noise Reduction function enabled. With this turned on and you are shooting at shutter speeds slower than one-half second, the camera will take two shots, one with the shutter open and the second with it closed. Any noise recorded on this "dark frame" is assumed to also be present in the actual image and gets removed accordingly. The function only kicks in for slow speeds even if it is enabled so many users (me included) leave it on all the time. But since your camera can't guess what the shutter speed will be several shots from now, the "r" number is always a worst case estimate, assuming that every shot will require noise reduction. The "r" number can also be a bit off for jpeg images since not all will compress equally.
Be forewarned that if you turn your camera off while it is in the process of offloading the buffer, it will finish the image currently being written, but any beyond that will be lost. When in doubt, let the little green LED that tells your camera is busy be your guide. So long as it is lit, don't turn off your camera. At least not if you just shot images that you want to keep I suppose.