In photography, the diopter is an often overlooked component on a DSLR. However, it is very important to have it adjusted correctly to get the most out of your camera. For some people (who are aware of the diopter), this will be the most basic of posts. For other photographers, this will be a moment of revelation and will save a lot of literal and figurative headaches.
Rotate the +/- knob to adjust the diopter
What is the diopter?
The diopter is used on anything with a sight, most notably, cameras and firearms. It is just an optical element, like a piece of glass, that magnifies the image and brings it into focus. Of course, focus is relative to each person’s eye. That is why some people wear glasses or contacts of varying prescriptions and some people do not. The diopter is used to adjust the focus based on each camera owner’s eyesight.
How do I adjust it?
Right next to the eye cup (the part you look through when framing up a photo) there should be a little knob. Put your eye to the cup and look through. You can do this with or without glasses on, depending on what you prefer. As you turn the knob you should see the focus change.
The best way to check the diopter focus is to take the lens or body cap off the camera. Make sure the camera is off while you are doing this and you are not in a location where there is a lot of dust in the air, since your sensor will be exposed. Adjust the little knob on the eyecup until the autofocus points appear sharp to you. There may be a range of sharpness depending on your eyesight. Put your lens back on and see if the autofocus appears to put things in focus.
Another quick way to check the diopter for focus is to use your autofocus points to focus on something very easy for the autofocus system to detect— a large subject with some sort of texture to it. Once your focus is locked, take a look through the viewfinder and adjust the diopter until the subject is sharp.
If everything looks blurry and you suspect there is something wrong with your autofocus system, check the diopter first. It may be that your images are turning out fine, but the viewfinder is blurry. Diopters can be easily messed with unintentionally while operating your camera or while the camera is moving about in a bag.
If you can’t get the diopter to be in focus at all you may need to get a different diopter or use your glasses or contacts with it. You can buy a custom diopter with a bigger viewing area, higher magnification, or one that is just more comfortable for use by people using eyeglasses. There are all sorts of aftermarket options for most cameras.
Also, make sure your lens is clean and your diopter is clean. Dirty glass can also make a difference in your ability to see a sharp image. I like to clean camera diopters with a damp Q-tip.