Depth of Field
with a camera like this, there is only one point of focus that is the focus distance. Anything in front of or behind that point of focus is actually out of focus, however, because the human eyes unable to resolve detail beyond a certain point. There is an area in front of and behind the point of focus. It appears to be sharp, and this is what we're referring to when we use the term depth of field. Now deaf, the field is influenced by two things. It's influenced by camera to subject distance. There's also influenced by the focal length of the lens that I'm using. However, it is controlled by lens aperture. A small aperture will give you a large depth of field. Large F number, large depth of field. A wide aperture will give you a small depth of field, small left, number, small depth of field. And I'm going to demonstrate that now, using this row of standing stones. So I have the cameras set up with the focus point on the first stone in the road on. For the purpose of this demonstration, ...
I've got F 2.8 set for lens aperture, a small left number, which is going to give me a small amount of depth of field. Take that picture now. If we look at that photograph, you'll see that the first stone is sharp. The second stone is sharp enough that you can see some detail, but it's starting to drop off. Even at this point in the 3rd 4th and the fifth Stones are all out of focus. So have a very narrow depth of field which has given me sharpness, really only from the first stone up towards the second stone. What I'm going to do now is I'm going to keep the focus point on the first stone. I'm going to set lens aperture. I have 22. So this is a very narrow aperture, a large F number, and this is going to give me a large amount of depth of field if I take this picture. What we see here is that if you look closely at the stones, not only is the first and the second stone sharp, but also the third going towards the fourth stone in the picture also have gained sharpness. So I've increased depth of field, have increased visible sharpness from the first stone to somewhere between the third and fourth stones. So with your narrowest aperture that your largest F number, you'll get the largest amount of depth of field. And with your widest aperture, that's the smallest F number. You'll get the smallest amount of depth of field. And, of course, you can change exactly how much sharpness you get in a picture from foreground to background. Simply by changing the F numbers, a medium F number will give you a medium amount of depth of field.