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

Sorry this is supposed to be in the third forum discussion.

-- (moschika), September 15, 1997.

This feature closes your aperture to show you the depth of field. It darkens because less light is passing through your lens. Look carefully at the darkened image, you should notice a difference in sharpness, depending on the change in aperture. This darkening is unavoidable, but only takes a little getting used to.

Be thankful you have the feature.

Use it wisely.

-- KEVIN PAUL (KPM927@aol.com), October 22, 1997.

As a practical matter if your working aperture is F22 or smaller it will be virtually impossible to see anything meaningful when you use your depth of field preview because the image will be too dark to see how the depth of field looks - you just can't see anything at extrememly small apertures, except perhaps in very bright light. At larger apertures (e.g. F8 and larger, perhaps F11 and larger depending on the light) it helps somewhat to move the depth of field preview lever very gradually. In this way your eyes can become accustomed to the darker image, so that when you finally are stopped down to the actual aperture you will be able to see things better.

-- Brian Ellis (bellis@fowlerwhite.com), December 04, 1997.

DoF

okie, when you press the DoF preview button on your camera, the apperture is closed down to the the Fstop that is currently selected (same as if it was going to take the picture, but the shutter isnt fired), thats why it gets darker. If you dont see what i mean, select a small aperture (like F32), look at the lense from the front, and press the DoF preview button, with most lenses you'll be able to see the aperture close down.

The smaller the aperture (the larger the value) the larger the DoF, i.e. the more is in focus (your lense may have markings on to help show this) with my Nikkor lense, if I select F32, and focus at 3 metres, then everything from infinity to 1.5 metres should be in focus (theoretically anyway!) wider apertures have smaller DoF, right down to F2.8, by which point only the exact distance that you focus on will be in focus. the DoF preview allows you to see for yourself what's in focus (although you do have to do it with limited light)

To test this out, make a small setup of objects at different distances from 1 metre to 10 or so, focus on an object in the middle and take 2 photos, one at F2.8 and one at F32 (if the lighting permits. - perhaps use a tripod) the difference should be clear from the prints, u should also get a rough idea from the DoF preview before u take the shot- thats what it's there for :)

good luck, hope that made sense!

Tim

-- Tim Coleman (timcoleman_@hotmail.com), November 11, 2001.