Telephoto lenses and shallow depth of field

The other thing we haven't talked about yet is telephoto lenses and their use in portraiture. Now it's pretty well known that they're a favourite with portrait photographers because they flatten the facial features making them look more appealing.

But another reason they're so popular is because of the way they really blur everything in front of and behind the point of focus. Now to get this effect the first thing you need is a wide open aperture (small f number say f2.8, f1.4 etc). And a full frame SLR camera is going to give you a shallower depth of field than a crop dSLR or a point and shoot.

All that being said, if you like to have blurry backgrounds the longer the lens you use the better it is. Take this shot here above. While the light on my aboriginal guide Vera isn't too bad for the time of day (middle of a sunny day in Aurukun, Cape York) the background is a mess.

Look at the light and shadows, gnarly branches and tree trunk, burnt out rocks on the ground. Just a really big mess that would relegate this picture to the junk pile. It was taken at a reasonably wide angle setting - 34mm on my zoom. Yuck.

Now look at what happens when I walk back a few paces and stick a longer zoom lens on and dial in 100mm.


Instantly that messy background of burnt out ground, jumbled branches and tree roots is a blurry, insignificant nothing. There are a couple of branches up in the top right hand corner that are a bit distracting but nothing as bad as the shot above.

So here the telephoto lens has done a couple of things. The narrower angle of view has cropped out the burnt out ground just behind Vera's body. The messy branches way off in the background appear closer but because they're so blurry they're not anywhere near as intrusive as the shot above.

And by having Vera larger in the frame she actually becomes the dominant feature. Plus the flattening effect of the telephoto lens makes her appear more natural.

Usually I like to move myself around to find a cleaner background but in this case we were in the middle of the forest and it was all as bad everywhere I looked. So I took the lesser evil and looked for trees that were far enough away to be blurred by the shallow depth of field. Just one more way that the background becomes really important in using your telephoto lenses.

Well that's covered the differences between wide angle lenses and telephoto lenses which should keep you lens fiends busy for a little while. Please if anybody has any questions or would like me to post on a particular topic write your comments after this post and I will help out where I can.

Have a great weekend and see you next week.