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[filmscanners] Re: Slide flatness

al@greenspace.freeserve.co.uk wrote:

> Most of my slides have been through a projector and have "popped" in the 
>process.  I
> assume that they never go back quite as flat.  Is this right?

No, they "pop" back.  Popping might actually flatten them further (see
the last paragraph).

What causes "popping" is the expansion of the film during heating.  In a
slide mount which doesn't adhere the slide to its edges in any manner
and has enough space for the slide to expand, the slide just comfortably
expands, and then contracts again as it cools.  This would make the
slide slightly loose and movable in its mount when the film is cold.

If, however, the slide mount attaches the film at the edges (as
cardboard mounts do, often restricting the movement of the film within
the mount for up to all four edges) or there isn't adequate space for
the enlarged film to move within, the film frame "pops" causing it to
become concave or convex to adjust (the extra size has to go somewhere,
so it distorts the middle of the slide).

When the slide cools, it shrinks to normal size.  The one potential
advantage to a slide being "popped' is that if it is a cardboard mount
with adhesive that was holding the film, it might break these bonds,
allowing the film to sit even more flatly afterward.

> > I'm still toying with getting a Coolscan 4000 and I wonder whether this 
>might take the
> plane of the film outside the DOF of the scanner.  Anyone had any experience 
>of whether
> there is a difference in scanning slides before and after projection?
> I guess the ideal workflow would be to scan newly processed slides before 
>projection (or
> glass-mount them which I'd rather not do).

There have been some reports here of one or two slide mounts which tend
to keep the image falter.  You might be able to get your lab to use
them, or you may have to provide them, in which case they should give
you a discount from the normal process and mount price to cover their
costs of the mounts they usually provide.


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