Re: Lenses Are On Order

[Tom Droege <droege@wwa.com>]

Chris and all,

The experts might comment on this.  My view is not to clean optics until
they get really dirty.  Say a loss of 20% or so in transmission.  Chris
says he has a lot of dust.  I would blow off what I could and just keep it
up week to week.  I think CO2 is used for this but the experts can comment.
 I figure that *I* will always do more damage by cleaning than it is worth.
 That is why the lens I sent Chris was in the state that it was.  I think
it had been out in the camera six months or so.   I think that lens also
has a couple of  "fungus" spots.  Chris, I could send you another from my
"collection" if you don't like that one.

I note that the objective lens is $92 each in the 80 quantity that it is
used.  We might run a few years and then just buy a new set of objectives
and replace them.  That would be cheaper than Chris's filter, would remove
one pair of surfaces.  

Comments anyone?

Tom 

At 04:37 AM 5/2/98 +0000, you wrote:
>Tom Droege wrote:
>> 
>> The subject says it.  I have grabbed the Tiger by
>> the tail, and we are now in for a ride with our very
>> own optics.  Let's hope it is a good decision.  40
>> lens sets are on order.  
>
>I don't know if you got my comments about this or not.
>I used an untested e-mail setup.
>
>First off this is good but unexpected news.  I thought
>you'd go with camera lenses at first.
>
>My comment was that these lenses will need frequent cleaning.
>The 135mm lens I have now was in need of cleaning as it had
>more dirt on the fron element then I'd like.  I now have a
>52mm "super multicoated" clear "filter" that will make normal
>cleaning easy as it can be removed and placed under running
>water to clean or at $20.00 replaced if damaged.  At my location 
>cleaning is required about weekly.  After a month you can 
>write with your finger in the dirt.
>
>The reason I bring this up is that I have seen what frequent
>cleaning can do to a muticoated optical surface.  It wears the
>coating off at best or scratches it at worst.  There are two
>easy solutions (1) cut threads in the lens barel to allow
>installation of a protective filter.
>The Mk IV would require a 125mm filter (I think.)  A good one
>costs just under $100.00  or (2) Tell the coating designer to
>use something very hard as the last coating layer even if it
>compromises the optical design.  Operators can be carful but
>"dirt happens". 
>
>
>-- 
>   --Chris Albertson             home: chrisja@jps.net        
>     Redondo Beach, California   work: chris@topdog.logicon.com
>
>
>