In article ,
Alan Browne wrote:
Martin Francis wrote:

Further, the film companies have differing emulsion build up designs,
including Fuji "4th layer" in some negative films. I never heard of
needing special lenses for that...


Or special lenses for black and white...

Good point.

I seem to remember a special three-layer B&W film from perhaps
the late 1960s or early 1970s. I have never used it, but I read the
reviews of it with great interest.

Each layer was a different ISO, and by selective color
filtration in the enlarger, you could select the layer which had what
you wanted.

IIRC, the review showed a shot of a clear glass light bulb, in
operation, and from one layer, you could get the image of the glass
envelope (with the filament vastly over-exposed), while from another,
you could get an image which showed detail of the glowing filament.

But, granted, this is an extreme example, and as far as I know,
the film had a very short life in the market -- just too special
purpose. :-)

Enjoy,
DoN.

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