DSLR Photo Tip, Using the Depth Of Field Preview Button!

Today's DSLR photo tip is about depth of field. Have you been using the "black button"? Continuing with our study of features your digital camera has - that you probably aren't using and may not be aware that exist - the depth of field preview button certainly qualifies!

This one, the "depth of field preview button" is not new to digital cameras or digital photography. It has been an added feature on most of the higher end cameras for decades! But, it's one of those things that, while we may know about it, few of us use on a regular basis.

What is the depth of field preview button?

To answer that question, let's take a quick step back and define depth of field. When you see a photograph, how much of it is in focus? Is it sharp from the foreground all the way to the horizon? Or is it so narrowly focused that the front of a fly's eye is in focus, but the back of that same eye isn't!

DOF is the amount of a photograph that is acceptably sharp and in focus.

The amount of a photo that is acceptably sharp can vary greatly from photo to photo depending on the lens used and the distance from the subject. (And your creative vision!)

A rule of thumb to predict the area of acceptably sharp focus is... Take the distance from the lens to the subject; the image will be sharp for a distance of about 1/3 of that distance in front of the focus point to about 2/3rds of that distance behind.

For example: Let's say you are shooting a large group of people and you have them posed in 4 rows. If you focus on the first row, the last one will be out of focus (or very soft). If you focus on the last row, the first one will be out.

If you focus on the third row, you still have a soft first row. But, focus on the second row and the first row falls in the 1/3 in front and the fourth row falls into the 2/3rds behind DOF range.

Before all you technicians write in... We don't need all the calculus formulas! The above is only an example! The actual depth will vary depending on the lens and the distance from the subjects!

By the way, you can increase the depth by moving further away from your subject and using a longer lens.

When you change the exposure settings on your lens or change the lens itself, the viewfinder is still going to show you the scene with the lens wide open. This is so that the lens can gather the most light possible to aid in setting up the shot.

Your lens won't stop down to the actual exposure settings until you finally depress the shutter button. What this means is that the scene you see in the viewfinder is NOT the way the final image will turn out.

Have you ever shot an outdoor scene where the background was nicely de-focused in the viewfinder, but in the final image all the background branches were in sharp focus? They look like antlers sticking out of your model's head!

That's because the viewfinder was showing the image with a wide open lens, (which has a shallow depth of field) but the final image was stopped down and sharper. Using the depth of field preview button would have shown you the problem.

Since the depth of field will vary from lens to lens and photo to photo, wouldn't it be nice to be able to see exactly how it will turn out BEFORE we shoot?

We can!

There is (on most of the better cameras) a little black button that - when depressed - will show you the image the way it is going to turn out! It is called the "depth of field preview button".

When you depress and hold this button - it is going to stop down the lens to show you the final image. Keep in mind that since you have been looking at the image with the lens wide open, when you stop down it is going to be letting in less light so the image is going to be darker in the viewfinder. Depending on your exposure settings, it could be a LOT darker!

Most of us don't use this feature because we either don't know about it, forgot about it or since it is darker, we think something got messed up.

Today's DSLR photo tip is to start using the depth of field preview button. It should be a regular check you make on virtually all of your photography. This will help you get the shot you pre-visualized and avoid potentially embarrassing mistakes.