[filmscanners] Re: [filmscanners_Digest] filmscanners Digest for Fri 27 Feb, 2004

["HPA" <tom@historicphotoarchive.com>]

Hello Bob, with all respect, I must disagree about condenser light, both
from the standpoint of theory and experience. Sharpness, and diffused vs
collimated light sources have been a raging debate for decades now, in so
far as enlarger light sources are concerned.  The most widely available
discussion is in Ansel Adams' book The Print.  Probably the most scientific
study as it applies to regular photography can be found in Dr. Richard
Henry's Controls in Black & White Photography second edition.  In summary,
equal sharpness is obtainable from either source. There is a substantial
difference in appearance, resulting mostly from the contrast index
(collimated light produces higher contrast, approximately one paper grade)
and the other notable difference is due to the Callier effect, which
accentuates contrast in the denser areas of film (accentuated slope on the
high values of the gamma curve).  Personally I have all types of light
source in my 5 enlargers, condenser and cold light, as well as the semi
diffuse like in the Leitz Focomat.  I have also used Besler point source
heads, which are the most extreme condenser (your lens aperture no longer
works when you use this).

Personally, I think minor differences in production models of scanners make
a big difference.  And I think that the temperature of the scanner light is
sufficient to cause minor softening of the image in any scanner because the
film expands a bit.  I can prove it on my flatbeds, but have not compared
slide scanners.  I measured the temperature of the film plane in a SS4000 at
93 degrees F (and about 72 ambient).  That is more than enough to cause some
unsharpness.  I only scan with glass on top of the film now, so this is not
a problem for me anymore, but it may be with others.

Tom Robinson
> Date: Thu, 26 Feb 2004 08:17:07 -0000
> From: "Bob Frost" <bob@frost.name>
> ----------------------------------------
> Tom,
>
> Surely the whole purpose of collimated light sources is to achieve maximum
> resolution (I seem to remember this from my light microscopy days many years
> ago). If you use diffuse light, you will not achieve max resolution: it's
> equivalent to blurring the image. The Minolta 5400 has a removable diffuse
> light filter, and if you switch it into position, you lose resolution, and
> the image becomes soft. You also lose resolution on the dust and scratches,
> but you can't have one without the other (as Doris Day used to sing).
>
> Bob Frost.
>
> ----- Original Message -----
> From: "HPA" <tom@historicphotoarchive.com>
>
> DIFFUSION OF LIGHT SOURCE: The Polaroid uses diffuse light, which minimizes
> dust and scratch marks on the base side of the film. The Nikon uses
> collimated light and this accentuates dust on the base side.  Of course the
> Nikon has the automatic dust removal, however that does not work with
> Kodachrome because the film is opaque to IR light.

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