What am I actully previewing? When i activate my DoF function on my camera the viewscreen darkens. how do I interpret this darkening as it relates to DoF. I understand that the darker, the more depth of field, due to how much the aperature closing. But that has really no meaning to what I'm seeing. What does the darkening viewscreen have to do with what the actual DoF in the final print.

-- (moschika@sirius.com), September 15, 1997

Answers

Try this. With an faily standard lens, set the focus to 5 metres, and the aperture the minimum, say f/22. Look through the SLR. Thisng 5 metres away should be in focus, but trees on the horizon will not. Press the DoF button. Sure, the image will get darker (because less light is getting through), but look carefully at the trees on the horizon. They should look much sharper -- in fact, about as sharp as if you had focused at infinity.

Because the image is darker, you do have to look carefully.

With some cameras, you can gradually press the DoF, which will progressively darken the image, and sharpen distances away from the sharp plane.

-- Alan Gibson (gibson.al@mail.dec.com), September 16, 1997.

Depth of field preview

Since the 60's, maybe earlier, most manufacturers made lenses that close down to the aperature at which you are shooting, as soon as you depress the shutter button. When you use your depth of field preview, the camera shuts the lens down to that aperature you;ll use at the moment of exposure and lets you "SEE" how much of your pic will be in focus. I didn't realize this when I began and always used the marks on the lens tops, and the little multi-colored lines that told me where my primary focus would be. Then, knowing something about the fact that the smaller your aperature-the deeper your focus would carry, I would adjust my aperature to where I thought it SHOULD be. Guess I played lucky for years. The darkness in the viewfinder is caused because the lens is temporarily closed down to the shooting aperature and you will have to look, carefully, to determine just where the focus breaks off and begins to soften. Remember: The larger the aperature-- the less "depth of Field". The smaller the aperature-- the deeper the depth of field.

-- H. David Huffman (craptalk@ix.netcom.com), May 12, 1999.

Or, focusing on the same subject, you could open the aperture up all the way and press the DOF button. There should be no change in brightness. Then, with the DOF still pressed, stop down and you will see the screen get progressively darker. Watch the background and you will also see it get progressively sharper....

-- brad schade (bcschade@aol.com), September 16, 1997.

depth of field preview

When you look through your viewfinder you are not acctually seeing what you will shoot with your camera. In complete truth you are seeing that image with the aperature wide open. When you snap the picture the aperature steps down to the setting you have given it. The reason is for ease in focusing. When you hold down the preview button the aperature is stepped down so the depth of field at the set aperature becomes viewable. and this is why the view gets dark. if this run on sentance explains anything at all.

have fun jason

-- Jason Smith (jasmith@laca.ohio.gov), October 20, 1997.