It is essential to learn how to focus when your cameras AF fails. When I first started using a digital SLR camera, one of the most frustrating problems I often came across, was when my lens wouldn’t lock on to where I wanted. Instead, it would constantly move in and out. Over time, I noticed a pattern to this annoying problem.
- The first thing to check is that you have the switch on the side of your lens set to AF or A (auto focus) and not MF (Manual Focus). This may seem obvious, however there have been many times when I’ve used MF and forgot to change it back to AF when required.
- Your camera may have trouble working properly in low light conditions. For example night shots. This is normal.
- You may find your lens swims in and out when photographing non contrasting subjects. For example, a cloudless blue sky or a wall that contains one solid colour.
- Photographing highly repetitive patterns like skyscraper windows or cars with reflective bodies can also cause problems.
- Personally, I find my lens sometimes has trouble if I’m taking macro shots and the insect or flower is constantly moving.
- Focusing on overlapping objects can also confuse your lens. For example, if you are trying to compose on the horizon, or say an animal in a cage. Times like these can make it hard for your lens to clearly know what it is you are trying to focus on.
- Sometimes AF may not be possible if you have an extender attached to your lens. Check your extender’s instruction manual for lens compatibility. Any other lens “add ons”, like magnification and closeup filters, can also cause problems.
What to do when AF Fails
Sometimes it’s not a matter of how to focus, but more to the point of where. Usually it’s just a matter of choosing a different point of interest. For example, if you are at the beach and can’t focus on the sand, try choosing the watermark line. Or if you are photographing a flower, try the very edge of the petal.
There will be times when your only option may be to use manual focusing. Also try focusing on an object within the same focal distance as the subject you are photographing. Then switch the lens to manual focus MF, recompose and take the shot.
An alternative to using manual focus is to focus on an object within the same focal distance, then use your camera’s ‘focus lock’ setting (check camera manual). At night time you may need to shine a torch on something nearby so you can lock focus. Don’t forget to switch your lens back to auto focus again for your next photoshoot.
Lastly learn how to use the lens infinity setting. This is especially useful for astrophotography.