DOF Preview??

[JohnQ]

Can someone explain to me what the depth of field preview button does on my 20d?

[studio206]

all it does really is give you a preview of your dof be4 you shot it without changing your focus o.O

[staticantics]

while looking through the lens when you push the dof preview it is supposed to give you an idea of what will be in focus. depnding on the quality of the lens you are using you may get varied results.

[duderton]

first of all, do you know what Depth of field is?? Say your shooting a portrait of some-one three feet in front of a tree. When you shoot whide open, say f1.4, your background will be blurry, thats a shallow DOF. If you stop down and shoot at f16 not only will your foregroud be sharp, but more of your background will be sharp. If you stop down even more, say to f64, both your foreground and back ground will be sharp as a tack. So say you set up your camera and you wanna see what will be in focus, you simply push your DOF button after you stop down and you'll know whats gonna be in focus. It's especially useful if you plan on shooting things stopped down, so you can determine if you want things to be in focus or not. It comes in handy, but eventually you'll be able to do it by eye.

regards,
rich

[JohnQ]

Thanks for all the help folks, I will give it a try tomorrow. I think it may be the quality of my lens thats stopping me from seeing a major difference. I will post my findings when I get a chance to experiment more. Thanks!

[duderton]

sure it makes a difference what kind of lens you use. What kind is it? If there isn't much of a difference between wide open an closed down, your not going to see a big difference.

[TX_Gulf_Coast]

DOF is affected by more than just the aperture or F Stop of the lens. Focal Lenght of the Lens, the distance to the subject and the F Stop all play a part in the DOF. Depth of Field is the plane that will be in Focus based on the factors mentioned. Example: on a 200mm F/1.8 lens (35mm) if the subject is 10 feet from you, everything about 9.96' to 10' will be in focus...you have a VERY shallow DOF. The opposite of this relationship is true as well. Same lens, F/32 subject 10 feet away, your depth of field increases to about 1.4 feet, as compared to the .08 of a foot at F/1.8.

With a shallow DOF, you have to be more selective in your focus, you do not have much room to play with. But it is a great tool in photography to learn and use.

Try it, shoot an image at your largest aperture (smallest F / number) then shoot the same image at the smallest (largest F / number). You can change your ISO to make the image work, that will have no effect on the DOF.