Depth of field

How often have you been wanting to photograph something and the camera has got the focus all wrong, instead of you it picked the background or worse, nothing at all and you got this:

camera gets focus wrong

If this is shitting you off, perhaps its time you took control of the camera and told it what to do!

One of the most handy physical facts of how a camera works, and one most often forgotten in this day and age, is the fact that as the aperture of a lens gets smaller, the range of things that are in focus gets deeper. This is to say that things closer to you and things further away from you will be in focus.

How close, and how far, well that depends on a few things, like the "F-Number" you've set as well as how far away the subject is.

Basically, the bigger the number the deeper the DOF is, and the further away the subject is, the deeper the DOF is .... easy :-)

So how does this look? In the image below I've taken a picture of something close, and put a ruler across the picture to see just how far the DOF extends. I took this picture at f5.6. You can see that barely 1cm is in focus. So, hover your mouse over the image, you'll see another image taken with a much larger f number (f16 actually). I had the camera set in Av. This means that I can change the fstop and the camera works out the shutter needed to keep the exposure the same.

hover mouse over to see deeper depth of field

So, how can we make this work for us? Lets say, you have a scene with Bill here standing about 5 meters away, and you want to get him in the shot, and have the beautiful mountain scenery hundreds of meters behind Bill also focused. You might wish for an image like either of these ...

but you probably don't want one like this:

You don't need any fancy modes on the camera, you just need some basic understanding how the lens focuses and you're set. The good news is that this is really quite easy, but only if your camera has some sort of manual focus. (If not, well, all you can do is half press the shutter to focus on Bill and hope for enough depth of field.)

So, do the following

• change your camera from fully Auto (probably called P) into Av mode. This is one of the most useful modes a camera can have for a photographer.
• (this step depends on your lens) set an aperture of something like f5.6 on a compact digital or f11 on a DSLR
• set the focus to MF, and move the focus point to around a bit further away that what you think the distance to bill is.

If you're using a compact digital camera then its even more likely you can just do away with auto focusing when your using wide angle! It works out that for most compact digital cameras that if you preset your manual focus to 3 meters, then everything from 1.7 meters to the sky will be in focus

TIP: This can be very useful when in the following situations:

• photographing through a window of a bus (can confuse autofocus)
• darker areas like old church building interiors where the camera probably can't even find focus
• candid moments when you don't want shutter lag or wait for focusing