What Is a Diopter?
In the most technical sense, a diopter is a measurement of refractive power on a lens that is equal to the reciprocal of the focal length. Pretty confusing, right? Here’s a better way to understand it. A diopter (strictly in the sense of how it applies to a DSLR or SLR camera) is a focal adjustment on the viewfinder that determines how well you see the image and information projected on the viewfinder.
The diopter adjustment is usually located right by the eyepiece in the viewfinder, and it’s typically a small dial, though it can be a slider in some older models of cameras. This dial adjusts the magnification through which you view the image and the image capture data (referred to as symbology) displayed within the viewfinder.
Most cameras have a standard diopter adjustment of +1 to -3, but it can vary slightly between camera models. If you need an adjustment outside that range, diopter lenses can be purchased for most popular cameras through you favorite camera vendor.
How a Diopter Functions in a DSLR Camera
In a camera, a diopter can increase or decrease the magnification used to display the image inside the viewfinder. This doesn’t affect the image displayed on the view screen, which is located on the outside of the body. It only affects the image and data displayed inside the camera when you’re looking through the viewfinder.
This image should be tack sharp when the image is in focus. If it’s not, it can lead to incorrect settings and focusing adjustments that will appear in your image. But don’t let that confuse you; the diopter doesn’t adjust the focus of the image you’re trying to capture through the lens of the camera, but only changes the focus of the image you see inside the viewfinder. This is why it’s possible to take pictures you think are perfectly in focus only to find in post-processing they’re not as perfectly focused as you thought.
Conversely, you can capture images you think are slightly out of focus, but turn out to be completely in-focus when you load the images to your computer and can see them on a larger screen. For this reason, it’s essential to have a correctly adjusted diopter when taking photographs.
How to Adjust Your Camera’s Diopter
Even a brand new camera can have an incorrect diopter adjustment. While you may think the diopter adjustment is perfect, it’s good practice to double-check the adjustment before you begin taking pictures. However, the adjustment methods are slightly different if you have perfect vision (which is considered to be 20/20) or if you wear glasses.
Diopter Adjustments If You Wear Glasses
If you wear glasses, then you already know you have vision problems that could affect the outcome of the pictures you’re taking. However, before you can adjust the diopter in your camera, you should first decide if you want to wear your glasses or remove them when taking pictures. This decision could impact the way you adjust your diopter.
If you’re going to shoot without glasses, take them off before proceeding. If not, then you can jump right into these instructions with your glasses in place.
Mount your camera on a tripod, and find something with high contrast on which you can focus the lens. Use Auto Focus to bring the image into focus. As you’re looking through the viewfinder, examine the image closely to make sure all parts of the image are in perfect focus. Also look at the symbolology at the bottom of the viewfinder screen to make sure it is in focus. If the image or the symbolology are out of focus, use the diopter adjustment to adjust the image until it and the symbology appear sharp inside the viewfinder. As you’re adjusting the diopter, move the dial left or right until you find the setting that brings your image into focus. Then, move the dial past that point until the image is no longer sharp and finally dial it back to the point the focus is the best. This is to ensure you don’t stop short of the perfect focus. Take a picture using the adjustment you just made, then load it onto a large screen to review it for focus. If the image is perfectly in focus, then your diopter is set correctly. If the image still appears slightly out of focus, repeat the instructions above to further adjust the diopter.
Adjustments If You Don’t Wear Glasses
If you have perfect vision or don’t need to wear glasses, your diopter can still get out of focus. A few simple adjustments (even adjustments on the fly) can make the difference between okay images and tack-sharp, stunning images. Here’s how to adjust the diopter if you have good vision and do not wear glasses.
Mount your camera on a tripod, and find something with high contrast on which you can focus the lens. Use Auto Focus to bring the image into focus. As you’re looking through the viewfinder, examine the image and symbology closely to make sure all parts of the image are in perfect focus. If the image or the symbolology are out of focus, use the diopter adjustment to adjust the image until it and the symbology appear sharp inside the viewfinder. Remember to find the focus, then move past it and back to ensure you don’t stop short of the perfect setting. If the image is perfectly in focus, then your diopter is set correctly.
How to Adjust the Diopter on the Fly
If you accidentally bump the diopter adjustment while taking pictures and you don’t have time to set up the camera on a tripod to readjust the diopter, you can make the adjustment on the fly by finding a high contrast frame in your current location.
Focus on the subject, make your adjustments to the camera, then continue taking pictures. In most cases, if you have good vision, this shortened version of the diopter adjustment activity is all you need to get back on track.
