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Date: 27 May 2007 14:41:17
From: JimC
Subject: Refinishing 16-inch mirror
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I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
which I understand might improve its optical performance somewhat and
enhance its reflectivity. It has worked great for viewing the Messiers,
but it doesn't seem to handle higher powers very well regardless of
collimation. Has anyone had this done, and what were the results? - I
don't want to get into doing the work myself, so costs, and the delay
time, are a factor. - I'm assuming that the finisher would first examine
the mirror and let me know whether he would recommend the work. Anyone
have recommendations for someone who might be available?
What's a reasonable estimate for a fairly decent, but not necessarily
professional quality job? Or, is it not usually worth the cost, meaning
that I should instead consider trading up to a better scope? - This is a
rather basic Telekit Dob with an old D16 mirror.
Thanks,
Jim
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Date: 27 May 2007 16:11:28
From: The Prophet Micah
Subject: Re: Refinishing 16-inch mirror
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On May 27, 6:50 pm, "Martin R. Howell"
<martinhow...@ilikestarsisp.com > wrote:
> On Sun, 27 May 2007 14:41:17 -0600, JimC wrote:
> > I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
> > which I understand might improve its optical performance somewhat and
> > enhance its reflectivity. It has worked great for viewing the Messiers,
> > but it doesn't seem to handle higher powers very well regardless of
> > collimation.
>
> What do you consider "higher powers" and what would you use them on? For
> my 12.5 inch dobsonian (f4.5), I generally push it no further than a 6mm EP
> and find that a 9mm EP generally delivers all the power necessary for the
> objects I observe. I do have a 3.8mm Orion Ultrascopic which gets little
> use at all. . .mostly for planetary observation when conditions are ideal.
>
> --
> Martin R. Howell
> Worldwide Amateur Astronomers
> Moderated sci.astro.amateurwww.theastropost.com/moderated_sci.astro.amateur
Ditto. On my XT-12 with 1500mm FL my favorite "high power" eyepiece
is a 7mm Nagler -- 214X. However, my 10mm Radian gets more use than
any other EP -- 150X. My 4mm UO ortho gets a little bit of use but
under excellent conditions only.
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Date: 27 May 2007 15:50:28
From: Martin R. Howell
Subject: Re: Refinishing 16-inch mirror
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On Sun, 27 May 2007 14:41:17 -0600, JimC wrote:
> I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
> which I understand might improve its optical performance somewhat and
> enhance its reflectivity. It has worked great for viewing the Messiers,
> but it doesn't seem to handle higher powers very well regardless of
> collimation.
What do you consider "higher powers" and what would you use them on? For
my 12.5 inch dobsonian (f4.5), I generally push it no further than a 6mm EP
and find that a 9mm EP generally delivers all the power necessary for the
objects I observe. I do have a 3.8mm Orion Ultrascopic which gets little
use at all. . .mostly for planetary observation when conditions are ideal.
--
Martin R. Howell
Worldwide Amateur Astronomers
Moderated sci.astro.amateur
www.theastropost.com/moderated_sci.astro.amateur
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Date: 27 May 2007 18:42:55
From: JimC
Subject: Re: Refinishing 16-inch mirror
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Martin R. Howell wrote:
> On Sun, 27 May 2007 14:41:17 -0600, JimC wrote:
>
>
>>I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
>>which I understand might improve its optical performance somewhat and
>>enhance its reflectivity. It has worked great for viewing the Messiers,
>>but it doesn't seem to handle higher powers very well regardless of
>>collimation.
>
>
>
> What do you consider "higher powers" and what would you use them on? For
> my 12.5 inch dobsonian (f4.5), I generally push it no further than a 6mm EP
> and find that a 9mm EP generally delivers all the power necessary for the
> objects I observe. I do have a 3.8mm Orion Ultrascopic which gets little
> use at all. . .mostly for planetary observation when conditions are ideal.
>
I would consider a 6mm EP (which would give about 305X in my scope) to
be high power.
Please understand that I have been using low powers, usually 50X, 70X
(35mm, 26mm eyepieces), for 99% of my viewing over the past several
years as I worked through the Messiers. - I'm now thinking of going with
somwhat higher powers for a change, using an equatorial platform, to
view planets and the moon.
Regarding comments in the previous note, at least one member in our club
does have some testing equipment and has offered to help me check out
the mirror. - We haven't been able to get together yet.
Thanks,
Jim
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Date: 27 May 2007 18:48:13
From: Dennis Woos
Subject: Re: Refinishing 16-inch mirror
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> I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
> which I understand might improve its optical performance somewhat and
> enhance its reflectivity. It has worked great for viewing the Messiers,
> but it doesn't seem to handle higher powers very well regardless of
> collimation.
On nights of good seeing, you should do a star test. Also, you should park
it next to another similar sized dob of known optical quality and compare
the views. How about a 7" off-axis mask - at f10 you should get great
planetary views. This will give you an idea of the quality of the mirror.
Of course, you can send it off to any numbr of optical shops who will
evaluate it for you, and refigure it if you decide it is worth it. However,
I don't think evaluating it yourself is that hard, and you will learn a lot
in the process. In our club, there are a number of folks who would gladly
help you (one guy even has a homemade interferometer) - aren't there any in
your club?
Dennis
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Date: 27 May 2007 14:44:54
From: Jan Owen
Subject: Re: Refinishing 16-inch mirror
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"JimC" <avocat5@sbcglobal.net > wrote in message
news:N1m6i.4602$C96.4531@newssvr23.news.prodigy.net...
> I'm thinking of having my 16-inch (2-inch thick) f4.5 mirror refinished,
> which I understand might improve its optical performance somewhat and
> enhance its reflectivity. It has worked great for viewing the Messiers,
> but it doesn't seem to handle higher powers very well regardless of
> collimation. Has anyone had this done, and what were the results? - I
> don't want to get into doing the work myself, so costs, and the delay
> time, are a factor. - I'm assuming that the finisher would first examine
> the mirror and let me know whether he would recommend the work. Anyone
> have recommendations for someone who might be available?
>
> What's a reasonable estimate for a fairly decent, but not necessarily
> professional quality job? Or, is it not usually worth the cost, meaning
> that I should instead consider trading up to a better scope? - This is a
> rather basic Telekit Dob with an old D16 mirror.
>
> Thanks,
> Jim
You might contact Steve Swayze...
http://www.europa.com/~swayze/refigure/refigure.html
--
Jan Owen
To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21
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