[LargeFormat] multi coating

[Michael Briggs]

On 02-Dec-01 Les Newcomer wrote:
> Okay so where does one go to get a lens multi coated?
> 
> les
> Ken Hough wrote:
>> 
>  I disassembled it and had it multi coated.


I am doubtful about the possibility to have any lens multi-coated except as
part of the original manufacturing process, at least at anything other than a
prohibitive cost.  To be effective, multi-coating must be designed for the index
of refraction of the piece of glass being coated.  How would an independent
repair service know this information?  Plus, the labor of applying the multiple
coatings in the correct thickness, different for each glass type, would be
prohibitively expensive (lens manufacturers do many lens elements
simultaneously, using an established procedure on a production line).  I
suppose someone in an optical lab could do it if they felt like it, ignoring
the cost of their own labor.

If you want multi-coating, the cost-effective way to get it is to buy a modern
lens (perhaps used) on which the manufacturer applied multi-coating.

I am aware of only one repair service that offers coating of lenses: Focal
Point, http://www.focalpointlens.com/fp_intro.html.  They don't specifically say
"single" or "multi", but their front page says that they use magnesium
flouride, which is the typical choice for single coating.   Their web pages
imply that their service is offered for repairing single surfaces of a lens and
is too expensive to apply to all air-glass surfaces of a lens.  They also warn
that coatings can't be applied to cemented groups because the cement would be
damaged by the heat of the process.

I have heard that decades ago, when single-coating was newly introduced, it was
fairly common to have existing lenses coated.

--Michael