[LargeFormat] multi coating

[Michael Briggs]

On 02-Dec-01 Ken Hough wrote:
> Multi coating is a VERY simple prospect. Search "vacuum coaters"
> "MF2 coating""metalic optical coating"  etc. There are many in the USA that 
> will do it.

MF2 (magnesium flouride) would be SINGLE coating.   It is the standard material
for single coating.  For multi-coating more than one substance has to be used
in order to have the several refractive indices called for in the design of a
particular multi-coat.

> The problem is the cost. and volume you want to send. 
My first sentence was "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."   We aren't really in disagreement.
Obviously multi-coating can be done, the question is whether it is possible to
have done on a used lens at a reasonable cost.

> I recement lenses as 
> a business. I wanted to offer coating better than I could do myself with my 
> 1947 B+L vacuum coater. I found a company in NJ that was reasonable and 
> did Multi coating. He would do just 6 elements as a minimum run. My cost 
> was 40.00 total. A good deal considering that the machine costs a couple of 
> hundred thousand dollars and takes an hour or so. Then he got greedy.
> After 3 years he raised his prices and the minimum number of elements went 
> to 50 at a cost of 40.00 each surface. Thats 4000.00 an order. He went out 
> of business.
> Ken 

My main doubt was whether after-market coating could be done in a
cost-effective manner.   For a while you had a supplier that charged a low
price, but then seems to have decided that the price was too low for the time
involved on a very expensive machine. If you can't find any other supplier that
charges such low prices, it is probably an indication that such prices are too
low to make a profit.  He then raised his prices to a prohibitive cost.  The
situation seems to be that either the supplier doesn't make money because they
charge too little for their costs, or they don't make money because their
charges are so high that no one uses their service.

Was this supplier coating only with magnesium flouride, or was this a true
multi-coating?   If it was multi-coating, how was the index of refraction of
the glass determined in order to select the correct coating design?

--Michael


> 
> 
> 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
>