[filmscanners] Re: film and scanning vs digital photography

["Arthur Entlich" <artistik@shaw.ca>]

There seems to be two main issues with depth of focus with film.  One,
when the image is captured within the camera, and two, when it is then
reproduced, either as a print, or made into a digital file.

With 35mm frames, in my experience, the second one is not that
significant as long as the digital scanner has a decent depth of focus,
which is determined by the aperture of the lens within the scanner.  On
standard optical CCD film scanners, at least with 35mm frames, if the
light source is sufficient, it isn't a great issue, and is easy to test
for...  either the grain (dye clouds) are evenly in focus or they
aren't.  The places I have seen a real problem are with larger format
films, which may require special mounting, glass carriers, or some other
method of maintaining flatness and with film scanners that have
inadequate light sources which lead to  needing to use a rather wide
open lens to capture the image, causing limited depth of focus.

The CCD flat bed scanners I have used seem to have substantial depth of
focus.  I have scanned 3d objects with very reasonable resolution and
sharpness.

The in camera issue is another matter. I don't know the actual depth of
focus at film plane different apertures allow for in camera.  Perhaps
someone has a chart that indicates the depth of focus relative to
aperture.  It would be interesting to know.  35mm film is physically
small enough that I expect the deviation is of less significance, but I
can see how larger roll films or sheet film could end up problematical.

Does anyone know if there is a chart which shows depth of focus at the
film plan versus aperture of lens used?  That could be valuable to know.

Art





James L. Sims wrote:

>All other arguments aside, flatness is much more important that some
>realize.  Back in the eighties, I had a lengthy dialog with a well known
>research lab about depth of focus  -  it ain't exactly what the American
>Cinematographer's Handbook says it is.  Film bows and sags.  That's hard
>to control.
>
>Jim
>
>gary wrote:
>
>
>>One last point here. Film will probably never be as flat as a piece of
>>silicon.
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