FreeLists / az-observing / [AZ-Observing] Re: Image Question

["William R Wood" <wmrwood@xxxxxxx>]

Stan,

I think Brian hit the nail on the head.  I did not know your scope was 25
years old or I too would have mentioned the issue of coatings and mirror
cleanliness.  A fellow D-K Cassegrain owner recently had his Tak Mewlon's
primary cleaned after 6 or 7 years and he said that the improvement in
performance was huge.  The Mewlon's owner's manual specifically mentions the
need for regular cleaning and also complete recoating of the mirrors after
some period of years - the period depends on how often the scope is used and
the conditions it is exposed to.  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.  There may be
places on your mirror(s) where the coatings are better/cleaner/smoother than
other areas and that could certainly account for the "edge effect" that you
are seeing.

Regards,

Bill Wood
Fountain Hills, AZ



> -----Original Message-----
> From: az-observing-bounce@xxxxxxxxxxxxx
> [mailto:az-observing-bounce@xxxxxxxxxxxxx]On Behalf Of Stanley A.
> Gorodenski
> Sent: Thursday, September 04, 2003 1:18 PM
> To: az-observing@xxxxxxxxxxxxx
> Subject: [AZ-Observing] Re: Image Question
>
>
> Bill, Matt, and Joe,
> My D-K is about 25 years old. It is a 12.5 incher from Coulter
> Optics when they
> were making some better mirrors. The phenomena I am seeing could
> be collimation.
> If I get a clear night tonight I will see if the more contrasty image is
> localized to one spot of the circular edge of the EP. The EPs I
> am using are a
> set I bought from Meade probably about 20 years ago. I noticed
> that the 10mm EP
> did not have as good an image as I thought it should. I contacted
> Meade and the
> owner (can't remember his name now) said that particular focal
> length was not as
> good. I assume from his response that the others were of good quality.
>
> When I said the markings are darker and there is significantly
> more contrast
> near the edge of the field, I meant at the very most edge of the
> edge, to the
> point where Mars almost vanishes from the field. At first I
> thought I might be
> observing some lint at the edge of the glass, but when I rotated
> the eyepiece
> the markings on Mars did not change. It almost seems like what I
> am seeing could
> be elevated in status to something called an "Edge Effect". Could
> there be any
> wave interference effects here? This is just wild speculation. I
> will check the
> collimation when I get clear night.
> Stan
>

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