Saturday, May 4, 2013

Why Won't My Lens Focus?

When I first upgraded to my DSLR camera and started using it extensively, I found myself facing a whole variety of problems, and for many of them, I couldn’t find easy solutions online or in any of my beginning photography books. I realized much later that some of these problems were so basic and fundamental that experts who had been shooting for a long time had likely forgotten that they had ever not known how to do such things.

This is the first article in an occasional series aimed at beginners called “Things Experts Forgot to Tell You” or “Things that You Forgot you had to Learn.” Maybe you’ve just purchased your first DSLR camera or perhaps you’ve had one sitting around for awhile that you’ve been meaning to start using.  The next big steps are getting out there, figuring out what you and your camera are capable of, and learning where to get answers to your questions.  While the first two steps are up to you, this series is an attempt to briefly cover some of the questions that might not have yet occurred to you to ask.

Why Won’t My Lens Focus?

Trust me, it’s not because your lens is broken.  Early on, I was convinced that I had broken my lens while trying to do some close-up photography.  I had gotten the bee on the flower nearly in focus and then my lens would make this terrible grinding sound and get stuck.  I was worried that something had gotten caught inside the lens itself and that the damage would be irreparable.  Neither the camera’s manual nor a quick search of the Internet provided any clues, and it wasn’t until sometime later that I found there was a very simple explanation.  

Each lens has a minimum focusing distance, which is a measurement of how close you can get to an object and still be able to focus on it.  This measurement is usually written on the lens itself somewhere.  For my Canon lenses, it’s written on the barrel of the lens, indicated with a little flower symbol.  For my kit 18-55 mm lens, the minimum focusing distance is 0.25 m / 0.8 ft.  The weird noises and inability to focus were caused by the fact that I was too close to the bee.

Why Won't My Lens Focus? | Boost Your Photography
Out-of-focus foreground plant with an in-focus background. I fell victim to the minimum focusing distance.

This early image of mine demonstrates the problem of minimum focusing distance. I wanted the leaves of the plant in focus, but the autofocus on my camera kept selecting the magazine in the background. I eventually gave up and just took the picture as is, not realizing that I only needed to get a little further away from the plant to keep it in focus.

If you are feeling limited by the minimum focusing distance of your lens, there are some inexpensive solutions. Close-up lenses act as a magnifying glass and allow you to focus on objects much closer to the lens. You can read all about close-up lenses and their benefits in this article. Purchase close-up lenses on Amazon.

Another reason that a lens may have difficulty focusing is because there are simply too many options for it to choose from.  This is particularly a problem if you have ever tried to photograph something obstructed like a bird in a tree.  You understand that you want the bird in focus, but the autofocus can get ‘distracted’ by all the various, overlapping branches in the way (or the film on your dirty window) and choose something other than the bird.  The best strategy here (other than trying manual focus) is to move yourself and the camera around until you have an unobstructed view of the bird.

Here the camera decided that I wanted the nice foreground branch in focus instead of either bird in the background.
Moving around slightly and waiting for better lighting gave me a much cleaner shot.
This picture was taken four minutes after the image above.
Bohemian Waxwing at Dawn by Archaeofrog on Flickr
Finally, your lens might have difficulty focusing because of a lack of contrast.  Autofocus relies on a contrast between the focus point and its surroundings.  If you try to autofocus on a blank wall or background, your camera will likely hunt back and forth without settling and maintaining focus.  To overcome this, you may have to put something on or against the wall or background for the autofocus to latch on to.  Similarly, your camera will have a much harder time focusing in low light, as a lack of light contributes to a lowered contrast.

Trying to focus on this blank wall  was not working.
In the picture above, I used the pictures framed on the blank wall to set the focus. Then I used the 10-second timer on the camera to put myself in the shot and check on the focus. After that, I switched the focus to manual to keep it in place, took the pictures off the wall, and was able to take a series of pictures of myself attempting classic Peter Pan poses. A bit of work in Photoshop combined the best pose with the best shadow for the final image.

Final Peter Pan image showing both the images combined for the final product.
Peter Pan by Archaeofrog on Flickr
So, if you are having problems getting your lens to focus, think about whether it might be for one of the reasons above.
  • If you are closer than the minimum focusing distance of your lens, you’ll either need to back up or use something like a close-up lens that changes the minimum focusing distance.
  • If your autofocus is having trouble finding what you want in focus, you may need to move around for an unobstructed view or give manual focus a try.
  • If your camera can’t find focus due to a lack of contrast, put something up against what you want to focus on and use that. Or use a flashlight or other lighting to add contrast to a dark situation before switching to manual to lock the focus in place.
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