Re: slide vs print

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Sun, 20 Apr 1997 17:08:04 -0500
>From: P3D ron labbe  <studio3d@xxxxxxxx>
>Subject: slide vs print

>John Roberts wrote:
>>Do you understand the reason for each step in the processing of slide film?

>What I understand is that the emulsion in the transparency image was burned
>by the very light that was reflected from the real objects that the image
>represents. First generation.

Bear in mind that the photons that exposed the film when the photo was taken
were consumed in the process of exposing the film, and no longer exist.
A transfer process must be performed by either optical (new light) or
chemical means.

>The emulsion in virtually any stereo print was not. Second generation.

Fair enough.

>Marvin Jones wrote:
>>I believe the premise here is that in the reversal process film is
>>developed, then re-exposed and developed a second time, thus yielding a
>>"second generation" image.

>Come on! RE-EXPOSED? To what? Not light! Because there's an extra bath it's
>second generation? Developer, reversal, color developer... there is no
>second generation- I just can't believe that there's an argument at all...

Hey - no fair sniping at Marvin behind his rock - he was just explaining my
original (and terse) statement.

The reversal step is what makes it second generation. If feeling that a
chemical reversal doesn't "count" makes you very happy, then please feel
free to go on feeling happy. Incidentally, the chemical reversal seems to
be a fairly recent phenomenon in the history of color slides - I have a 1975
book on darkroom methods which states that the Unicolor E-6 process is more
convenient than the Unichrome process, because Unichrome uses physical
reversal by re-exposure to [white] light, while Unicolor uses the newfangled
chemical reversal. A 1970 encyclopedia only mentions the light exposure
method of reversal.

I haven't come across any claim that the switch from physical re-exposure to
chemical reversal made any difference in the image quality. Which highlights
the point that this issue of "generations" is of little or no relevance
to 3D photography. How a slide *looks* is more important than how many
"generations" it's been through, so generations are not much of a selling 
point. The appearance is one of the things that encourages many people to
use slides, despite some of the inconveniences.

John R


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