"Cheesehead" wrote in message
...
On Feb 9, 11:41 pm, "Richard Knoppow"
wrote:
If its a standard Triplet the back cell will be a single
lens so there is no need to remove the glass. The front
cell
will have two elements. Usually in larger lenses there is
a
threaded back cap on the cell but it may have a retaining
ring on the front which is more common for smaller lenses.
If a back cap its easy to remove. The elements are clamped
between concentric edges in the cell so are automatically
centered.
If the cap is too tight for removal with simple finger
grip use one of those rubber jar grippers. It won't mar
the
surface. If you grip too tightly it will clamp it and make
it even harder to remove.
I agree with the others about cleaning but if the lens
is oily the standard optical cleaner is pure acetone
followed by dry isopropyl alcohol. Window cleaner like
Windex may streak the lens if not followed by alcohol. The
newer butyl alcohol "streak-free" cleaners are better.
While ammonia is alkaline and strong alkalies can
dissolve some kinds of glass there is no real danger from
the very dilte ammonia in Windex and similar cleaners.
If you use acetone be careful of the edge paint, if any,
and of the paint on the cell because it will dissolve
both.
I do not recommend cleaning inside elements when in a
shutter because there is too much danger of getting the
cleaning fluid into the shutter, take the cell out.
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Richard Knoppow
Los Angeles, CA, USA
I'm not absolutely certain about the Geronar formula. It is
reported
to be a Tessar.
That said, the rear should be a single piece of glass. But
it is not.
If it is a cemented piece, then it is not a true Tessar and
the
fogging may be in the cement.
That would be bad.
I've not found the formula out there to describe the lens.
In the mean time I've been searching for a replacement rear
cell.
I think you mis-typed, a Tessar _does_ have a cemented
rear component, a Triplet does not. I also don't remember
what a Geronar is but think it may be a Dialyte. Have to
look it up. If it is a Dialyte its a four element air spaced
lens. Both front and rear cells will have two lenses with an
air space between. There should be a back cap on both cells
allowing access to the inner surfaces.
If its actually a Tessary type and there is haze inside
the rear component its due to the cement being damaged. Most
old lenses were cemented with Canada Balsam. This has good
optical properties but is subject to damage from low
temperatures, which will make it milky. It also tends to dry
out at the edges unless very well sealed, so that its common
for CB cemented lenses to show a yellow ring of oxidation at
the edge. If this goes on long enough the cement at the
edges may crystalize. While a small amount of oxidation at
the edge (its not true separation) does little harm it can
cause problems if it progresses far enough. Most of these
lenses can be recemented. Modern cements are synthetic,
either binary cements similar to common epoxy or UV curing
cements. Some lenses built in about the 1950s have an
earlier synthetic cement of a type cured by heat. Some of
these show degradation or true separation due to problems in
the cementing process. I've seen a number of Kodak lenses
that seemed slightly hazy but on close examination with a
magnifier and correct light, it was evident that the cement
layer had become reticulated, having a sort of orange-peel
look. Some Zeiss lenses and some Wollendak lenses from this
period have actual large bubbles in the cement where it has
completely separated from the glass. All these can be
recemented if they are thought valuable enough. One can try
it at home using a makeshift method of centering but any
valuable lens should be submitted to someone like John van
Stelten who has the proper equipment to do it the right way.
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Richard Knoppow
Los Angeles, CA, USA
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Richard Knoppow
Los Angeles, CA, USA