Re: [Leica] Painful separation

[echampio <echampio@Adobe.COM>]

> Hi,
> 
>  Pardon my ignorance.  I have never had or seen a lens with separation, so
> do not know what it looks like and what effect the separation would have in
> picture taking.  Any light on this matter will be appreciated.
> 
> Regards,
> David

Hi,

Here's the text of a message that I saved that explains element separation
very well:

>   The appearance varies depending on what kind of cement was used and what
> has happened to the lens.  Lenses cemented with Canada Balsam typically
> start separating at the edge where the air can get at the cement. Usually
> it starts by discoloring and getting yellowish or brownish. In time this
> discolored area will begin to crystalize giving a granular appearance to
> the separated area.  Balsam which has been subjected to excessive heat can
> turn milky but it tends to do that all over.  If the lens has been
> subjected to mechanical shock the Balsam may start separating in feathery
> looking lines all over the lens surface.
>   Synthetic cements seem to separate in "bubbles" which are visible when a
> light is shown though the lens.  The white ring may be separation,
> especially if it is on the periphery of the lens but may also be something
> deposited on an inner surface.  Shining a flashlight through the lens often
> will tell you where a problem is.  The cemented interfaces will show some
> reflection and the quality of the reflection will be affected if there is
> any irregularity in the cement.  I have a Kodak Ektar which shows an
> "orange peel" surface this way.  This degradation of the cement shows up as
> a slight diffusion of the image.
>   It is also possible for a white deposit to be fungus but that is usually
> in round spots or feathers.
>   Lenses can often be opened for cleaning without too much trouble.  The
> retaining rings can be removed by employing a washer made of latex turned
> with a tool like a bottle cap which is the right size.  This way of removal
> can also be used on retaining rings with slots since it is much less likely
> to mar the ring or lens than using a spanner.
>   Lens surfaces can be cleaned with lens cleaner, like Kodak Lens Cleaner,
> whic is a dilute solution of Ammonium Carbonate with some detergent added.
> The standard optical shop degreaser for glass surfaces is reagent grade
> Acetone.
>   Use the Acetone with care because it will dissolve the anti-reflection
> paint from the edges of the glass and also can damage other painted or
> plastic surfaces including lens cement.  Usually, the lens cleaner will
> take off anything on the lens but sometimes the Acetone is necessary.
>   I've found that most older lenses have a coating of haze on the inner
> surfaces.  My guess is that this comes from residual plasticizers
> evaporating form the paint in the lens over many years.  It comes off
> easily.  Many older lenses are flary because of this haze rather than lack
> of coating.  Getting rid of it makes a surprizing amount of difference.
> - ----
> Richard Knoppow
> Los Angeles,Ca.
> dickburk@ix.netcom.com
> ----------

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Erich Champion : mailto:echampio@adobe.com  : 408.536.6497 Voice
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