Photography Lesson No.1. Selective Focusing.

As explained in my earlier post, "Photography Lessons. Why?", this post will concern the technique needed to show a girl in a crowd highlighted by being in sharp focus while all around her are out of focus. Easily obtained in a few seconds with your camera and without spending hours editing your photographs with Adobe Photoshop or similar picture editing software. The technique can be equally applied to any number of subjects, it is often used to photograph a small flower head in sharp focus with a blurred background for example.

Selective Focusing in this case is created by adjusting Depth of Field. Depth of Field is the amount of a subject either side of the main focus point which is still in focus, i.e. the amount in front and behind which is still in focus. In the case of our girl in a crowd there should be very little in front and behind her in focus i.e. we require a narrow depth of field.

So how do we create this? Simple, we adjust the f stop on the lens aperture ring. A small f stop number which gives a large aperture, say f2.8, will provide a narrow depth of field so few children if any in front or behind our girl will be in focus. A large f stop number which gives a small lens aperture, say f16, puts a great deal in front and behind our girl in focus. It's as simple as that.

Now, like all creative techniques it is best to practice before you use them for real. If you are lucky enough to have a digital SLR you can take as many practice pictures as you want at nil cost so there is no excuse. If you have a SLR film camera you can still practice reasonably well using the preview function. I suggest that if your camera offers an 'aperture priority' setting you select it now as it gives you much less to worry about particularly if you want to take actual photographs during your practice session. To practice I suggest you find something like a picket fence or similar which has clearly defined uprights, focus on something about 2 metres away and set the lens aperture to about f2.8 or the smallest number (widest aperture) you have available. Now either by taking a photo or using preview have a look at how much is in focus, hopefully the upright you set your focus to and very little in front or behind it. Now as a comparison set a large f stop number, say f22 which gives a small aperture, and compare the difference. You should now have not only your chosen upright but nearly everything else as well. I recomend that you now try the same exercise with several f stops in between to get the feel of what happens with your particular lens and camera. The more you do this the better because the best pictures are nearly always taken 'on the hoof' and previous practice will greatly increase your chances of success. There is a small cheat you can use, if you look on your lens you should find a depth of field guide which will help you to know approximately how much will be in focus. I say approximately because they can be a little crude and cannot replace experience gained with your equipment.

So that's the basics of Selective Focusing using Depth of Field. At this point I should point out that depth of field changes with the focal length of the lens, a wide angle lens will have less depth of field than a telephoto, so if you have more than one lens you should practice with them all or at least the ones you use most. If you have a zoom lens like an 18-135mm then the amount of depth of field will change greatly between the 18 and 135 settings.

Hopefully all is clear. If not please ask me questions via a comment. Additionally if you have any questions on photography I would enjoy answering them, it will help me know what to put in my next Photography Lesson.

Now, "Go Out And Practice".