Checking Optics of 10" Dob in Day Time?

I'd like to check the optics of my Dob during the day and before this
evening. Are there some simple tests I can run? I can at least, I think,
get it into a dark area. We have many windows. I could take to an office
where it is very dark.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews

You can do a pretty decent job of collimating it using a sight tube
and/or a laser collimator, but other than collimation I don't know what
you intend to change about it before tonight. Here's a good
collimation article that I use.

http://www.efn.org/~mbartels/tm/collimat.html

Mark


W=2E Wat son wrote:
I'd like to check the optics of my Dob during the day and before this

evening. Are there some simple tests I can run? I can at least, I
think,
get it into a dark area. We have many windows. I could take to an
office
where it is very dark.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City,
CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39=B0 15' 7" N, 121=B0 2' 32" W, 2700
feet
=20
Web Page: home.earthlink.net/~mtnviews

On Wed, 09 Feb 2005 17:31:00 GMT, W. Wat son
wrote:

I'd like to check the optics of my Dob during the day and before this
evening. Are there some simple tests I can run? I can at least, I think,
get it into a dark area. We have many windows. I could take to an office
where it is very dark.

Unless you have a Foucault Tester set up, about the only optical
check you can do in an office is collimation.

Outside, you may be able to do a rough star test, if you can see
sunlight glinting off of an electrical insulator about 1/4 mile
away. Even then, thermal problems may hamper your efforts.

For collimation instructions or Foucault software check the
appropriate linkes at

http://www.vvm.com/~piscescs/sponsored.html

Cheers,
Larry G.

Larry G wrote:

On Wed, 09 Feb 2005 17:31:00 GMT, W. Wat son
wrote:

I'd like to check the optics of my Dob during the day and before this
evening. Are there some simple tests I can run? I can at least, I
think, get it into a dark area. We have many windows. I could take to
an office where it is very dark.


Unless you have a Foucault Tester set up, about the only optical
check you can do in an office is collimation.

Outside, you may be able to do a rough star test, if you can see
sunlight glinting off of an electrical insulator about 1/4 mile
away. Even then, thermal problems may hamper your efforts.

For collimation instructions or Foucault software check the
appropriate linkes at

http://www.vvm.com/~piscescs/sponsored.html

Cheers,
Larry G.


Thanks.I should have mentioned it is well collinated. I did it about 4
months ago. However, I'm interested in resolution and related matters that
might tell me how well it might be able to split doubles, or divy up the
bands of Jupiter and the rings of Saturn.

Years ago when I ground a mirror I used a homemade Foucault tester, but
I've long forgotten how to use one.
--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews

W. Wat son wrote:
I'd like to check the optics of my Dob during the day and before this
evening. Are there some simple tests I can run? I can at least, I think,
get it into a dark area. We have many windows. I could take to an office
where it is very dark.

John Dobson tests all of his telescopes in the daytime by using the sun
glint off a power pole insulator as an artificial star.

Mojo
--
Morris Jones
Monrovia, CA
http://www.whiteoaks.com
Old Town Astronomers: http://www.otastro.org

Thanks.I should have mentioned it is well collinated. I did it about 4
months ago. However, I'm interested in resolution and related matters
that might tell me how well it might be able to split doubles, or divy
up the bands of Jupiter and the rings of Saturn.

Years ago when I ground a mirror I used a homemade Foucault tester, but
I've long forgotten how to use one.

Star test is really the easiest way if the mirror is in the scope. This
won't give you quantative data like the foucault test, but it'll give
you an idea of how well the mirror is parabolized. A glint of sunlight
off of a shiny object at a distance would work.

By the time you read this it'll be dark and you can just test the scope
on doubles, Jupiter and Saturn. Even a foucault test doesn't guarantee a
good mirror. There are other factors such as astigmatism, rough surface,
etc, which the foucault test will not take into consideration.

-tom

vic20owner wrote:

Even a foucault test doesn't guarantee a
good mirror. There are other factors such as astigmatism, rough
surface,
etc, which the foucault test will not take into consideration.

The foucault test is and EXCELLENT test for roughness. Carl Zambuto
uses
the foucault and ronchi consistantly and has no problem guaranteeing
mirrors of outstanding quality, and that includes measuring
astigmatism.
Anyone incapable of confirming a good mirror with the foucault test
isn't using it propery. It does, of course take practice.

Dan C.

The foucault test is and EXCELLENT test for roughness. Carl Zambuto
uses
the foucault and ronchi consistantly and has no problem guaranteeing
mirrors of outstanding quality, and that includes measuring
astigmatism.
Anyone incapable of confirming a good mirror with the foucault test
isn't using it propery. It does, of course take practice.

I agree that it's possible to detect these errors with foucault, however
a "simple" foucault test will not -measure- them. It takes experience
to recognize roughness and astigmatism. I was in no way bashing the
foucault test. A simple foucault test on the hubble mirror would have
saved NASA a ton of time and money.

-tom

Why not just go outside and look at Jupiter, Saturn, some doubles, and the
like? Do this for several nights because seeing conditions will vary from
night to night.

--

-----
Joe S.



"W. Wat son" wrote in message
ink.net...
Larry G wrote:

On Wed, 09 Feb 2005 17:31:00 GMT, W. Wat son
wrote:

I'd like to check the optics of my Dob during the day and before this
evening. Are there some simple tests I can run? I can at least, I
think, get it into a dark area. We have many windows. I could take to
an office where it is very dark.


Unless you have a Foucault Tester set up, about the only optical
check you can do in an office is collimation.

Outside, you may be able to do a rough star test, if you can see
sunlight glinting off of an electrical insulator about 1/4 mile
away. Even then, thermal problems may hamper your efforts.

For collimation instructions or Foucault software check the
appropriate linkes at

http://www.vvm.com/~piscescs/sponsored.html

Cheers,
Larry G.


Thanks.I should have mentioned it is well collinated. I did it about 4
months ago. However, I'm interested in resolution and related matters that
might tell me how well it might be able to split doubles, or divy up the
bands of Jupiter and the rings of Saturn.

Years ago when I ground a mirror I used a homemade Foucault tester, but
I've long forgotten how to use one.
--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: home.earthlink.net/~mtnviews

On Thu, 10 Feb 2005 01:03:19 GMT, vic20owner
wrote:


I agree that it's possible to detect these errors with foucault, however
a "simple" foucault test will not -measure- them. It takes experience
to recognize roughness and astigmatism

Actually, Carl does measure astigmatism with the simple foucault test
and the couder mask. My experience is that large and medium scale
roughness is VERY easy to recognize and I had no problem seeing this
in my ealiest mirror making days. Micro-ripple is tougher to confirm
and requiring some experience, but not as damaging as large and medium
scale roughness.

Dan