Information on Newton Rings and history of solving the problem in
rings are created when is trapped between two smooth surfaces like glass
and film. As light from your scanner or enlarger passes through this air
pocket it’s refracted. This
refracted light creates an interference pattern first noticed by Sir
Isaac Newton. They look
somewhat like the circular rainbow effect of gas on water.
the photographic process there are different methods of getting rid of
Film Holder s
most obvious is to use a glassless film holder.
Since the film is suspended over an opening there is no
possibility of creating Newton Rings.
While this is effective, glassless holders have their own set of
problems. Since there is no
overall support for the entire film area the center may be in a
different focal plane than the edges.
This causes soft focus at the edges of your scan. Also,
film can expand due to internal heat of the scanner or enlarger.
Since the film is typically rigidly held in place by clamps, as
it expands the only place for it to go is up or down.
So the center is ultimately thrown out of focus.
has been used to flatten film during darkroom exposure virtually since
gelatin base substrates were invented.
Almost immediately photographers began noticing Newton rings on
their enlargements. It
didn’t take long to figure out where they were coming from.
You only had to look at the film holder in the right light and
see the rings. It was also noticed that Newton rings almost exclusively
occurred between the smooth base of the film and glass.
The emulsion, it was determined, was “rough” enough to not
cause trapped air.
is where the experimentation began.
All sorts of solutions were tried.
Starch, baby powder, or other fine powders- These were placed in an
atomizer and a small amount sprayed into the air, creating a thin cloud
of dust. Film was waved within the cloud and some particles settled on
the film. It was then sandwiched between two sheets of glass.
The dust, in theory, allowed air to escape from between glass and
film. Since photographers
are usually clean freaks in the darkroom this method didn’t have much
of a following.
is an excellent method for eliminating Newton rings.
To use this method, photographers build or purchase a fluid mount
film holder frame. It’s
designed to hold two sheets of glass and contain mounting fluid within
the frame. Film is
sandwiched between these two sheets of glass with a slight film of fluid
between film and glass. The
fluid prevents air pockets from forming and eliminates Newton rings.
drawback is that before the digital revolution negatives were hand
retouched with dyes. The wet mount fluid removed any retouching dyes, so
the technique fell out of favor. Fluid
also can attract airborne dust to the negative.
most retouching is now performed digitally, fluid mounting has made a
small come back.
success has been achieved by sandwiching film between optically coated
glass. The glass coating is much the same as used on camera lenses and
reduces reflection and refraction of light passing through it.
In theory the coating causes light to travel through any existing
air pockets with less or no refraction.
The high cost of this glass has prohibited wide spread
experimentation or use so the jury is still out on its effectiveness.
glass first came into wide spread use in the late 1960’s.
Enlarger manufacturers were desperate to find a solution of
Newton rings for their professional clients.
Photo labs were creating wall size prints and needed to sandwich
film between glass to ensure overall print sharpness. Unfortunately
Newton Rings were causing high paper wastage.
The Newton rings were being enlarged along with the negative and
couldn’t use fluid mounting due to heavy use of negative retouching,
and glassless carriers allowed a small amount of film curl at the edges
causing soft focus in those areas of the print.
are no records on file crediting any specific person or company with the
invention of AN glass for photographic purposes.
But, with some experimentation, photo labs found it effective and
a relatively inexpensive method of solving the Newton Ring problem.
glass can have its problems depending on how it’s used.
most vexing problem with using any glass sandwich and film is
environments, poor film cleaning and glass cleaning techniques cause
dust problems. In any
glass/film sandwich you have to clean 6 surfaces.
But, benefits far out way the problems. Dust
spots can be retouched from prints and files, Newton rings cannot.
two sheets AN glass together can soften an image when enlarging or
extra sharp light created by condenser type enlargers can cause the AN
glasses texture to show up in broad even areas of a print.
Background paper and cloudless or overcast skies are typical
problem areas. The advent of
diffused light enlargers has eliminated this problem in the darkroom.
scanned at high resolution (typically over 4,000 dpi) can cause the
glass texture to show in digital images.
of the newer films have very thin emulsions resulting in the occasional
Newton Ring. Using two sheets of AN glass can solve the problem but at
medium resolution and above you may see image degradation.
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