Does Lens Focal length sway Depth Of Field?

For some time now I have been reading reports about this and trying to outline out how it should sway my digital photography.

[b]Lens[/b]

The basic interrogate is: Does a wide angle lens (smaller focal length) furnish more depth of field than a telephoto (longer focal length) lens?

This has been taught to us in the textbooks and the photo magazines for a long time and it appears that you get more depth of field with a wide angle lens than you do with a telephoto lens.

If you crusade the Internet for "depth of field", you will not look long until you come over many articles that say that using a wide angle lens does not increase depth of field.

Tests have been conducted by many, together with some of the photography magazines, that prove that depth of field is not dependent on the focal length of the lens being used.

This is a very technical issue and technically it is true. You can even conduct similar tests or experiments to verify it for yourself. However, from a practical standpoint what does this mean to me, the photographer?

All of the data that I have seen so far is based on the hypothesis that you keep the image size the same.

The test goes something like this: using a zoom lens, take a photograph of some subject using a telephoto or long focal length setting. Then zoon out to a wide angle or shorter focal length setting. You could also do this with interchangeable fixed focal length lenses, one telephoto lens and one wide angle lens.

Now, advance some section of the photograph taken with the wide angle setting so that the image in that section is the same size as the image in the selfsame section of the photograph taken with the telephoto setting.

Upon examining the resulting photographs, you will find the depth of field is approximately the same in each of the photographs. There is basically no difference. So, you have proven that technically zooming out to a wide angle focal length did not increase your depth of field.

But, let me ask you a question. Why do you zoom out or switch to a wide angle fixed focal length lens in the first place?

Suppose that you are standing out before some great mountain scene that is beautifully lit with sunrise colors. You zoom in to a telephoto setting and take a picture. Then you zoom out and take a photograph using a small focal length setting.

You want and expect to see more depth of field in the second photograph - all the way from the flower in the foreground to the sunlit mountain peeks. And that's what you appear to get.

Will it cross your mind that if you blow up a section of the second photograph that you will lose all that apparent depth of field? No, the greater depth of field still appears to be in the photograph taken with the wide angle focal length setting.

You zoomed out so that you could get a wider view and a larger depth of field or at least the perception of more depth of field. You also knew that the images would appear smaller.

Same for zooming in, you wanted to make the image appear larger and you also knew that there would be a perception of less depth of field.

From a practical point of view when you change focal lengths seldom if ever, will you zoom in or out with the idea in mind of keeping objects the same size.

Using different focal lengths, zooming in or out, gives the perception that depth of field changes. What you get with the wide angle lens appears to have more depth of field than what you get with the telephoto lens.

Technically this may not be the case.

But, what is all of your photography about? The main riposte is: what appears right to you. So, I say unless you are a stickler for technical correctness stick with the old time proven rule.

· If you want more depth of field, or you want it to appear that way, use a shorter focal length lens or zoom out.

· If you want less depth of field and a larger image of some part of the scene, zoom in to a longer focal length setting.

This will still give me the photographic results that I want. I have taken a gorgeous photograph of a mountain scene and my zone of sharpness appears great.

To me this technical revelation does not change the way I take my photographs. What about you?

After all, this is your art that you are creating. Don't let the pure technical explanation get in the way of you creating what you want to create.

Continue to pretend that a wide angle lens gives you greater depth of field than a telephoto lens. Your results will show it.