Another question I have been asked a number of times is “what in the world is this small wheel by my viewfinder?” That “wheel” is called the diopter and it serves a very handy purpose for those that need it. I included a shot here of the top of a Canon camera with the diopter circled in red.
Not everyone has 20/20 vision, many people wear glasses or contacts to make up for our eye’s natural failings and this is where the diopter comes in. When using a camera, it is often not comfortable to wear your glasses as they tend to get in the way. I personally have glasses but only need them for reading and only then because my right eye is slightly weak.
The diopter allows people that normally wear glasses to use their viewfinder without them and still see clearly, although it’s use is primarily only for shooting using manual focus. The diopter has no marking index or starting point, you simply look through your viewfinder without your glasses and if the viewfinder seems to be blurry then adjust the diopter slowly one way or the other until the readout becomes clear. Below is a shot of the viewfinder as you look through it.
The diopter only has adjustment from -3 to +3, so it might not be able to compensate for everyone’s vision, some people who are extremely near or far sighted might need to purchase a custom diopter lens to be added to their camera to make their viewfinder clear and sharp for their eyes. It is also possible for the diopter to accidentally get bumped and out of whack for your vision, just tune it back to your eyes and everything is back to normal for you. If you are in a situation where you share your camera with a friend or family member, the diopter will need to be adjusted each time one of you uses the camera.
Now that you have a better understanding of that tiny wheel next to your viewfinder, adjust yours to your eyesight and then get out there and make some great images!