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Re: [Rollei] "Balsam" issues with some Zeiss lenses?



Richard

I have had great success using acohol at RT
for separating cemented lenses and filters.

Jerry


Richard Knoppow wrote:

> At 01:30 PM 11/06/2001 -0000, you wrote:
> >Joe B. wrote:
> >
> >"A repairman I spoke to tonight said he's seeing a lot of Zeiss lenses from
> >the
> >60's with what people call balsam problems- he says it is actually optical
> >cement and not balsam that is giving this problem with these lenses."
> >
> >I've heard this too, from a specialist Rollei repairer in London. The lens
> >we were discussing was the 135mm f4 Sonnar in the Tele-Rollei, and he warned
> >me to check *very* carefully for this effect. His optical specialist has had
> >the cemented elements of two Tele taking lenses sitting in a bath of
> >whatever-it-is-they-use-to-take-them-apart for over *twelve months* and they
> >won't separate (so they can't recement them).
> >
> >www.ffordes.co.uk has three Tele Rolleis for sale on its site, and when I
> >enquired about the lens condition by mail a few weeks ago I was told that
> >two of them had separation problems in the taking lens.
> >
> >--
> >David Morton
> >dmorton  uk
> >
>   FWIW, A company called Summers Optical makes optical cements and
> solvents. Their web address is:
> http://www.emsdiasum.com/Summers/optical/cements/default.html
> Even if you
> are not interested in taking on recementing yourself the primer here makes
> interesting reading.
>   Synthetic cements have been used for nearly all lenses from the late
> 1940's. A few manufacturers began using them even earlier especially for
> aerial lenses for use at high altitude. These lenses are subjected to
> temperatures which will almost instantly crystalize Canada Balsam, making
> the layer cloudy and the lens useless.
>   Many kinds of cements have been used. The early ones were mostly
> thermosetting. While synthetic cements should have a much longer lifetime
> than Canada Balsam there are subject to some problems in assembly and
> curing. I've seen some lenses, including Zeiss lenses for the Contarex,
> which had what looked like large bubbles in them. This is the cement
> separating. I have also seen a few Kodak lenses where the cement layer has
> become turbid, looking like wax paper.
>   Many lenses can be recemented. If the elements are not completely
> separated the technique is to bathe the lens in a hot solvent solution. The
> solvent Summers sells operates at around 340F. The problem is that
> sometimes the thermal shock can cause the elements to fracture. The
> Summer's solvent is started cold to avoid this problem. Once separated the
> lenses can be cleaned with Acetone and pure Ethyl alcohol and recemented.
> Summers sells both binary type and UV setting cements. I've used the
> conventional binary type. This requires curing at 130F for an hour. There
> is also a room temperature curing cement but I prefer to have the longer
> working life of the mixed cement. The temperature is not critical and the
> recementing procedure is not too hard to do.
>   Most cemented elements have edges which are carefully centered. When
> these are clamped together the entire assembly will be centered correctly.
> The difficulty comes with lenses with different diameter elements, such as
> the Schneider Angulon. I've not recemented a finder prism but would guess
> that its practical to do.
>   Steve Grimes also has a little on lens re-cementing on his web site
> http://www.skgrimes.com
>   He uses prisms to clamp the lens edges. I've found that even large
> machine nuts seem to be suitabley square. A sheet of thick glass is used as
> the reference surface. I've used an ordinary gas oven for curing although a
> temperature controlled electric oven would be ideal.
>   I have also recemented using Canada Balsam, but it is actually more
> difficult and fussy to use and the results are not as good.
>   Lenses cemented with Canada Balsam can be gotten appart by gentle
> heating. The text books say to use a frying pan but I've also had good luck
> placing the elements in water and heating it until the fall apart.
>
> ----
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk  

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