My what? Your view into the camera's lens might be blurry even if your lens is in focus. Your diopter adjusts your eye piece on your camera in accordance to your vision. Neat, right? Did you know it was there? Or maybe you always saw that little dial but didn't pull out the manual to see what it did?
Most brands of DLSRs have a dial of some type to the right of the eyepiece. Nikon’s can be big or small and obvious, Canon’s is a bit smaller. They function the same on both systems. That little dial on a camera typically has an adjustment range of -3 to +3, with 0 being the idea of 20/20 vision. If your eye-site is anything less than average, this dial will be your best friend to help shoot better photos, especially if you attempt to use manual focus.
To set the diopter correctly, you will need to set your camera on a tripod and point it at something flat with enough texture to be easily seen. Press your shutter release halfway down to force your camera with auto-focus. Without moving the camera, turn the diopter control until (with or without glasses) the image is in focus to your eye. Really that is all there is to it! Maybe this tip will help you if you believe your focus is a bit out on your camera?