Some digital cameras have a diopter adjustment that helps improve the clarity of the viewfinder. By adjusting a dial, lever or knob located near the viewfinder, sharpness and focus changes. Since the diopter is connected only to the viewfinder, the focus of the camera lens itself is not changed nor does it affect autofocus.
You may be able focus the viewfinder to match to your eyesight, be it near or farsightedness. In some cases, you may not have to wear eyeglasses when using the camera.
As the dial is rotated, the viewfinder image comes in and out of focus. Make sure the camera lens is focused before making any adjustment. Make adjustments while actually looking through the viewfinder until the scene is sharpest.
Preferably, if your camera has focus brackets, keep your eye on them until they come into sharp focus. Remember, it’s the viewfinder that you want matched to your eyesight.
A word of caution
Be careful not to stick your finger in an eye while making diopter adjustments!