Film-Tech Forum ARCHIVE: Depth of Field or Depth of Focus?

This is topic Depth of Field or Depth of Focus? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Iben Jimenez (Member # 3713) on 06-05-2006, 05:33 PM:

Greetings
In photographic terms, the depth of field is the space in front and behind the subject where it can be photographed with sharpness, and depth of focus is the space behind the lens where you can move the film plane and still have a sharp focus. But in terms of film projection, Where is the depth of focus and where is the depth of field? Is the depth of focus the space behind the lens, and depth of field the space in front and behind the screen?
Thanks for your help?
IJ

Posted by Bobby Henderson (Member # 840) on 06-05-2006, 06:35 PM:

"Depth of field" is only relevant in what is actually captured in the photograph itself. Different lens types, the size of negative, amount of lighting and length of exposure time when making the photograph will all affect depth of field. Once the image is photographed, it might as well be etched in stone. The depth of field is set permanently.

Depth of field can range from everything being in razor sharp focus all across the image to where the focal plane is reduced to a mere sliver of thinness. At that point only a small part of the image is sharply focused while everything else in the frame falls off into a blur. Either extreme and various points between can be used to great dramatic effect.

When projecting the image, you really only want to get the image dialed in as sharp as possible and with an appropriately bright, even amount of light. There's lots of stuff to balance in that. But depth of field is not one of them. Still, the auditorium must be designed properly and the projector, lamp strength, lens type and all sort of other stuff must be carefully balanced to get that image dialed in to proper brightness and focus as closely as possible.

Posted by Iben Jimenez (Member # 3713) on 06-05-2006, 06:52 PM:

If I move the film plane in the gate as it happens when you have film flutter, you are altering the depth of focus of the lens and would have a loss of sharpness. Equally if you have different distance in the screen as in a curved screen, the sides would be out of focus due to the difference in distance if the curve is not shallow. So my question is, If the depth of focus tolerance is only in the distance behind the lens, what about the curved screen issue?

Posted by Adam Martin (Member # 641) on 06-05-2006, 07:29 PM:

This has been discussed already at What is depth of focus, depth of field and lens stop?

And you started the other thread, too! [uhoh]