Just to add to potential confusion: X-ray film traditionally had emission on
both sides of the support base, the better to capture said X-rays; essentially
higher speed and the resolution wasn’t impacted for the purpose. In my time,
Tri-X was only coated on one side, so any multi-coat must refer to layers.
Kurt in SoDak
On 20 Jul 2018, at 16:18 , Helge Nareid <hn.groups@xxxxxxxxxxxx> wrote:
I would imagine that the main driver for scattering in emulsion is total
emulsion thickness (other factors would of course also influence it, such as
grain size). This is all from fallible memory, but I seem to recall reading a
paper showing that thinner emulsions, all else being equal, would have a more
limited tonal range, but would be sharper. Using two different emulsions
improved tonal range while retaining total emulsion thickness. Fairly modern
emulsions, such as Tri-X, tend to be relatively thin, even though they may
consist of two (or more) layers. Older, thicker, emulsions such as Super-XX
Pan were less sharp, but had beautiful tonality, which worked very nicely in
large format, where film sharpness is less critical. Late colour films
frequently had multiple layers for each primary colour.
- Regards
The Horrible Helge
PS: I don't have any reference materials to hand, so this is all from
(fallible) memory.
On 20/07/2018 21:46, `Richard Knoppow wrote:
I think Bob Shanebrook is a member of this list, perhaps he could answer
the question.
What I know is that many films of the past had two emulsions, on slow,
one faster, and of different contrasts, in order to increase the range of
exposure (lost the correct term for this). Double coating helps with this
but can reduce sharpness because of greater scattering in the emulsion.
Bob will have a better answer I am sure.
Some color films have many coatings to adjust the tone rendition of each
color.
On 7/20/2018 1:27 PM, Dana Myers wrote:
On 7/20/2018 1:08 PM, Richard Lahrson wrote:
I recently asked a question about Tri-X and got no response.
It is about Tri-X being a 2 coat emulsion. What's the difference
between one and two coat manufacturing of film?
rich
I'll have to dig out Robert Shanebrook's 'Making KODAK Film' and
see if I can get some idea. Or perhaps Robert will fill us in.
Cheers,
Dana K6JQ
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