Modern cameras, especially DSLR’s, use autofocus systems to help focus the view/subject you see through the viewfinder. Before these systems were introduced the only option you had with a SLR was to focus the lens manually (by the turning of the focus ring on the lens) until the image as seen through the viewfinder appeared sharp.
Nowadays we rely on autofocus. Depending on how your camera is configured you will see a number of autofocus points in the viewfinder that flash once focus is achieved on that particular focus point(s). You may also hear a beep also indicating that focus has been achieved. Whether you have all focus points active or just one is up to you. One thing to remember is that the central focus point is the most sensitive.
Some Photographers just have the centre focus point active and will use this exclusively. They do this by positioning the centre focus point over the the area of the subject that is the prime point of focus (e.g. the eye if it is a portrait of someone). They lock focus by half depressing the shutter button and then move the camera to compose the shot all, the time keeping the shutter button half depressed (maintaining focus lock). Once they are happy with the composition they completely depress the shutter button.
There are times however when the camera struggles to achieve focus. The reason for this is that you may be shooting in low light or there is little contrast in the scene. So what can you do? One option is to focus the lens manually.
Turn off the autofocus by moving the button/slider on the lens to the manual position. You can now focus by turning the focus ring on the lens until the image appears sharp. However, you should always ensure that you have calibrated your viewfinder according to your eyesight as the judgement on whether the subject is in focus or not will be based on what you see through the viewfinder.
Most cameras have a viewfinder dioptre adjustment facility. This is a small wheel that sits behind the viewfinder (normally a wheel showing a +- scale).
You can follow this simple procedure to set this up correctly.
- Find a notice, sign or maybe a magazine or newspaper.
- Use the camera as you would normally. If you wear glasses or contact lenses when you use the camera, keep these on.
- Affix your camera to a tripod or stablise it in some way so that it does not move.
- Look through the viewfinder and focus the camera on the text using the autofocus.
- Switch the autofocus off and do not move the camera.
- Look through the viewfinder and rotate the dioptre adjustment wheel until the image appears at its sharpest.
- Once you are happy, leave the adjustment in this position for all of your photography. You should only need to change it if your eyesight changes or you have a change in glasses or contact lenses.
- Please note that this does not affect the autofocus on the camera, it merely changes how sharp the image appears to you as seen through the viewfinder.
If you share your camera with someone else the chances are their eyesight will be different to yours and that they will see unsharp images when they next use the camera.
We cover this topic and also the autofocus functions in our Getting Started course.