[AZ-Observing] Re: Image Question
- From: "Jack Jones" <spicastar@xxxxxxxxxxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Fri, 5 Sep 2003 17:51:11 -0700
It's not just a desert, but a city in the desert, so air pollution is the
big threat. We have corrosive substances in the air, sulfur dioxide, ozone,
carbon monoxide, nitrogen dioxide, and all that powdered rubber tire gunk
floating around plus smoke in the winter if there's an inversion layer
around. It may take 25 years to get thru something like Beral etc. if stored
properly. I'd worry more about my lungs, but I wouldn't wait two years to
clean that stuff off my mirror.
Back to the image question, I'd say what's driving availability is market
demand. You are not going to easily find any "mirror greater than 16 inches
before 1980" because we had no place to put a mirror like that unless we had
a govt grant. But you did have excellent mirrors. ~1980 was the start of the
Dobsonian revolution and only then did big mirrors appear in quantity, some
few of which were excellent, which is what we are talking about. We may not
be talking about the same thing, excellence, not size, cost, f.l., or
availability. The excellence was due to the skill of the artisan, as stated
before, who then found he could actually get paid for making big ones, like
his own.
Cave Optic's up and down quality is absolutely typical isn't it? The small
company hit with huge backorders, sounds familiar doesn't it. Good, Cheap,
Fast - pick any two.
Jack
> Bill Wood wrote:
>
> > The new Tak mirrors are coated with real high tech stuff that lasts a
> > long time but none of the Tak dealers suggest that they will last as
long
> > as 25 years without recoating.
>
> Is this true even here in Aridzona? Other than a lot of dust, what
> attacks coatings in this climate? Shouldn't mirror coating last for
> decades in the desert, or am I misinformed again?
>
> In the misinformed department, I will ask if it's not "technology"
> (Austin Powers quotes added for effect) that is improving mirrors today,
> what is it then? I defy you to find a good mirror greater than 16 inches
> in diameter and faster than f/5 made before 1980 that was available
> commercially for a reasonable price. Today, the shopper has many
> options. What were an amateur astronomer's options 20 years ago?
>
> Tom
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