[pure-silver] Re: donut solution; enlarger lens problem
- From: Georges Giralt <georges.giralt@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 11 May 2007 22:56:12 +0200
Shannon Stoney a écrit :
Are Newton rings really named after Isaac Newton? If so, why?
--shannon
Because he discovered the phenomenom and described it.
Newton rings appear when two perfectly matching surfaces are in close
contact. (being flat or not, it is sometimes used to control lens
curvature)
The base of the film is made of perfectly flat plastic, so when in
contact with optical glass which is prefectly flat, Bingo ! here are the
rings ! By slightly frosting the upper glass in contact with the base,
one destroys the perfect flatness of the glass surface leaving no room
for Mr Newton ... because the flat film does not find the flat glass
anymore.
On contrary, the emulsion side of the film is not perfectly flat. During
proessing, silver clumps are formed which modify the gelatin thickness.
Of course, in minute amounts, but this is enough to destroy the flatness
avoiding Newton rings.
If you have to print neg upside down, i.e; gelatine up, you CAN'T put
the anti newton glass in the bottom of the neg carrier BECAUSE frosting
it has destroyed it's optical quality, it will difuse the image too much
to give you the fine result you expect...You may have luck removing
bottom glass and tensioning the negative to keep it flat. This is
sometimes trickier if the neg is at the edge of the film strip...
--
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S'il vous plaît, aidez nous à conserver nos ressources,
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