As we often find people complaining that their lenses do not focus properly or they are back or front focused or they cannot produce sharp images! However most problems with apparently out of focus images are down to bad technique or a lack of understanding of how autofocus works. So I decided to try and give a little tutorial on how to focus and what to look out for.
First the myths.
Myth 1: You can always sharpen up an image in Photoshop.
This is true but focus and sharpness are two different things. If the image is out of focus you will just end up with a sharp out of focus image!
Myth 2: Shoot with a small aperture to get a wider focus area.
While using a deeper depth of field with a smaller aperture can improve the “apparent” sharpness of a photograph. There can only be one focal plane, so if the focus is out things will relatively look out of focus. And this will get worse as you sharpen. You can normally see this in portraits where the eyes looks OK but once you see the tip of the nose in better focus the eyes then look slightly soft. This type of problem can often be corrected by selectively sharpening things like the eyes but it is no substitute for the correct focus in the first place.
Now the tips…
Before you start taking pictures check your diopter setting. The small wheel next to the eyepiece should be adjusted until the viewfinder information (the numbers at the bottom or to the side) look crisp. Adjusting this will not help your camera focus but it will help you see if things do not look right.
How does the camera focus? When you look through a viewfinder of any SLR you normally see squares which light up red when you half press the shutter. If the camera is on defaults it will look almost random as these squares light up. They are in fact picking up the different focus points in your picture – normally the closest bit to the camera. The camera will then calculate an average focal plane for the image. This can work fine for a typical snapshot of the kids in the garden but not for things where you what to place the focus on a specific point (like the eyes) in a portrait. As we get better as photographers we want more control and focus is a key skill so:
Tip1: Focus mode
Unless you are shooting action shots like Birds in Flight or Football Games keep your camera in one shot mode rather than servo mode. Why… well in servo mode you camera is trying to predict movement of the subject and the focus is constantly hunting. The camera is also choosing the focus points itself so you will not be able to choose the plane of focus yourself and your image will only have the correct focus by chance rather than design.
Tip2: Center point Focus
Unless you are shooting action photographs, set your camera for center point focusing in one shot mode. This uses just the single square in the center and only focuses as you half press the shutter button. Why… well the center point is the most sensitive on all cameras and is always a cross type sensor (meaning that it can recognize both vertical and horizontal edges) most of the other focus points can only sense focus in one direction unless you have a very expensive camera.
Tip3: Set you focus points to show on preview
This will enable you to see where the focus point is upon review in the camera screen and ensure you are at least getting the focus in the right place.
Tip4: Focus Recompose
This is where you place the focus square over the area you want to focus on (leading eye in a portrait for instance) half press the shutter button and then (whilst keeping the shutter half pressed) move the camera back to the correct position to compose your shot and fully press the shutter.
Do it properly – the things to watch…. Keep your body still and try to only move your head and arms with the camera. I have seen people take a small step back or lean backward to compose the shot after focusing and then wonder why the image is not sharp. Also it is surprising how many people release pressure off of the shutter button as they recompose and when they take the shot they find the have focused on the chin not the eye! Some cameras have what is called back button focus this allows you to use a button on the back of the camera to hold the focus with your thumb and then you just press the shutter normally to take the shot.
Though not really related to focus, there are a lot of circumstances where lack of sharpness is blamed on focus where the focus is perfect but the image is still blurred or lacks clarity. Since sharpness is determined by a line of contrast, if you are underexposed or have flat lighting, an image will not appear sharp even if other focus criteria are met.
Tip6: Shutter speed
Blurred images that are focused properly or often down to subject movement or camera shake. You need to ensure you have the correct shutter speed for your lens. As a rule of thumb you can handhold a wide angle lens at 1/30 or 1/60 but for telephoto lenses use the “1” over rule which is the closest shutter speed to the focal length of the lens ( 200mm lens = 1/200 and 100mm lens = 1/125). Image stabilized lenses (IS/VR) allow hand holding a stop or two lower so maybe 1/125 or 1/160 for a 200mm lens but they will not freeze action so moving subjects will still be blurred. Another thing to remember is that camera shake is worse the further away the subject is from you so… adjust your shutter speed accordingly.