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[ATM] Re: Another Astigmatism question, but at the sphere stage
Thank you all for the ideas on this astigmatism question. I will check out the images. James and Jerry, I have seen some of that non-circular stuff on the mirror in the past, although by the time I got to my parabola the first time it seemed to have disappeared - nevertheless Sixtests indicated multiple ROCs and I did see eliptical shapes in the star test that first time.
I have gone ahead and star tested this newly oblate, TUE, sphere, and I do see some elliptical shape to the diffraction pattern, although much less than before. **Also, the ellipse seems non-existent when centered in the field, but as the star slides up and off the diagonal that's when the ellipse really shows up stronger.** So, I will rotate the mirror 120-degrees in the cell and test again tonight.
I'm feeling much better about the situation after having done the star test. Worst case, I am moving in the right direction, and more, gentle 1/4 to 1/3 COC strokes, rotating both the top and bottom pieces as I go, should take care of it. Not sure how long it will take, however. Best case, my further star tests tonight should nail down the source of the astigmatism, and maybe it's just in the diagonal. Maybe I'll put some woven rubber shelf liner under the mirror when I mount it tonight to further even out the pressure on the back, although 1.3 inch pyrex shouldn't have much of an issue anyway.
I'll also run a couple further Foucault tests to see what sort of standard deviations in the ROC output I'm actually getting from Sixtests - probably really small, especially since my input data is from sample means of 3 test runs.
Jay
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Today's Topics:
1. Re: Another Astigmatism question, but at the sphere stage
(James Lerch)
2. RE: Another Astigmatism question, but at the sphere stage (Jerry)
3. RE: Another Astigmatism question, but at the sphere stage
(Guy Brandenburg)
4. Re: Another Astigmatism question, but at the sphere stage
(john sherman)
5. FW: [ATM] Another Astigmatism question, but at the sphere
stage (James Mulherin)
6. FW: [ATM] Another Astigmatism question, but at the sphere
stage (Jerry)
----------------------------------------------------------------------
Message: 1
Date: Sun, 28 Aug 2005 19:01:46 -0400
From: "James Lerch"
Subject: Re: [ATM] Another Astigmatism question, but at the sphere
stage
To: "ATM"
Message-ID: <009801c5ac24$771badf0$6402a8c0@NewToy>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
----- Original Message -----
From: "Jerry"
>Can someone provide Foucault and Ronchi images of this astigmatic mirror?
Jerry,
I have archived 120+ unmasked Foucault images on mirror C, here:
http://lerch.no-ip.com/atm/MRR/
Click on Mirror C Results at the top, Section #3, sub-section 3 (Between the
robo Foucault results and the interferometry results)
BTW, each image is flawed by a small speck of dust some where in my CCD camera.
The flaw shows up as a small 'blotch' in the bottom center of each image.
Hopes this helps.
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)
"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"
" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
Calvin Coolidge
------------------------------
Message: 2
Date: Sun, 28 Aug 2005 19:17:53 -0400
From: "Jerry"
Subject: RE: [ATM] Another Astigmatism question, but at the sphere
stage
To: "'James Lerch'" , "'ATM'"
Message-ID: <002001c5ac26$bc476f20$0100a8c0@D85SJB21>
Content-Type: text/plain; charset=us-ascii
Ok! Thanks James. And the astigmatism does show in those images.
Jerry
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
James Lerch
Sent: Sunday, August 28, 2005 7:02 PM
To: ATM
Subject: Re: [ATM] Another Astigmatism question, but at the sphere stage
----- Original Message -----
From: "Jerry"
>Can someone provide Foucault and Ronchi images of this astigmatic mirror?
Jerry,
I have archived 120+ unmasked Foucault images on mirror C, here:
http://lerch.no-ip.com/atm/MRR/
Click on Mirror C Results at the top, Section #3, sub-section 3 (Between the
robo Foucault results and the interferometry results)
BTW, each image is flawed by a small speck of dust some where in my CCD
camera.
The flaw shows up as a small 'blotch' in the bottom center of each image.
Hopes this helps.
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating
site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)
"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"
" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
Calvin Coolidge
_______________________________________________
ATM mailing list http://www.atmlist.net/
------------------------------
Message: 3
Date: Sun, 28 Aug 2005 16:21:52 -0700 (PDT)
From: Guy Brandenburg
Subject: RE: [ATM] Another Astigmatism question, but at the sphere
stage
To: Jerry , 'James Lerch'
, 'ATM'
Message-ID: <20050828232153.96508.qmail@web40512.mail.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
If you can see the astigmatism in those 2 knife-edge
images, you either have much better eyes, or a much
better imagination, than I do. Are you serious, Jerry?
Guy
--- Jerry wrote:
> Ok! Thanks James. And the astigmatism does show in
> those images.
> Jerry
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net
> [mailto:atm-bounces@atmlist.net] On Behalf Of
> James Lerch
> Sent: Sunday, August 28, 2005 7:02 PM
> To: ATM
> Subject: Re: [ATM] Another Astigmatism question, but
> at the sphere stage
>
> ----- Original Message -----
> From: "Jerry"
>
> >Can someone provide Foucault and Ronchi images of
> this astigmatic mirror?
>
> Jerry,
>
> I have archived 120+ unmasked Foucault images on
> mirror C, here:
>
> http://lerch.no-ip.com/atm/MRR/
>
> Click on Mirror C Results at the top, Section #3,
> sub-section 3 (Between the
>
> robo Foucault results and the interferometry
> results)
>
> BTW, each image is flawed by a small speck of dust
> some where in my CCD
> camera.
> The flaw shows up as a small 'blotch' in the bottom
> center of each image.
>
> Hopes this helps.
>
> Take Care,
> James Lerch
Guy Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
------------------------------
Message: 4
Date: Sun, 28 Aug 2005 19:49:32 -0400
From: "john sherman"
Subject: Re: [ATM] Another Astigmatism question, but at the sphere
stage
To:
Message-ID: <200508281949.AA1164312708@mail.johnspics.com>
Content-Type: text/plain; charset=us-ascii
Hi Jay,
>My question is whether it's too early to judge astigmatism,
>since I'm only at the sphere stage,
Isn't it better to find and fix it now? You can use a pinhole and an eyepiece to do a star test from the radius of curvature, and there won't be any spherical aberration to contend with. You should be able to detect a tiny astigmatism in the image from the separation of the source and eyepiece, but it will not rotate with the mirror.
Of course, you can replace the eyepiece with a spot for a different view. It's the 2D version of the Foucault, and it does see astigmatism.
>Where is everybody?
I was out observing till 4am. :)
John
johnspics.com/a
------------------------------
Message: 5
Date: Sun, 28 Aug 2005 20:44:42 -0500
From: "James Mulherin"
Subject: FW: [ATM] Another Astigmatism question, but at the sphere
stage
To:
Message-ID: <20050828184501.FE12FDE1@dm17.mta.everyone.net>
Content-Type: text/plain; charset="us-ascii"
> Jay:
>
> If your mirror is close to spherical the Ronchi test offers a good check
> for astigmatism. If you can move the grating through focus while holding
> one grating fringe dead center in the mirror you can watch for rotation in
> the fringe. Ideally, you will see no rotating in the fringe as it moves
> through focus. If you see rotation this indicates astigmatism.
>
> You can also check for astig on a star, even with an uncoated mirror. Look
> at the star inside and outside of focus. If the defocused star looks
> elliptical inside and outside of focus this indicates astigmatism. The
> long axis of the elliptical star will change by 90 degrees depending on
> whether you are inside or outside of focus.
>
> In an 8" F/6 I would say the risk of astigmatism is pretty low, assuming
> you are using a fine anneal Pyrex blank. If you're using plate glass I
> wouldn't be surprised if the astigmatism is real.
>
> James
>
> James Mulherin
> Optical Mechanics, Inc.
> jcmulherin@opticalmechanics.com
> www.opticalmechanics.com
> Tel: (319) 351-3960
> Fax: (319) 351-3943
> > -----Original Message-----
> > From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
> > Of J Killea
> > Sent: Saturday, August 27, 2005 7:47 PM
> > To: atm@atmlist.net
> > Subject: [ATM] Another Astigmatism question, but at the sphere stage
> >
> > As long as nobody tells my family about the trouble I'm having with this
> > mirror, I should be able to keep working on it!
> >
> > After doing star tests and trying to resolve detail on Jupiter, I
> decided
> > I had some intolerable combination of TDE and astigmatism in my 8" f/6
> > blank. Did some nice, gentle polishing to get back to sphere (an oblate
> > one) and I've got a nice TUE that I can live with for the moment.
> >
> > HOWEVER, I just did three sets of Foucault measurements along each of 2
> > diameters and Sixtests (set to "Target b=0" with variable ROC
> calculation)
> > came back with the ROCs of each diameter differing by about 0.5mm.
> That's
> > more delta than what I had when I thought my parabola was done the first
> > time.
> >
> > My question is whether it's too early to judge astigmatism, since I'm
> only
> > at the sphere stage, and whether Sixtests with Foucault data is even a
> > valid way to judge astigmatism. I might just stick it back in the
> 'scope
> > for a star test, and hope that the radical amount of SA I will see will
> > not make it too difficult to discern just the astigmatism.
> >
> > Is it time to go back to AlOx #15 or 20? (Please say it ain't so!)
> >
> > As always, thanks a ton,
> >
> > Jay
> >
> >
> >
> > ---------------------------------
> > Start your day with Yahoo! - make it your home page
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
------------------------------
Message: 6
Date: Sun, 28 Aug 2005 22:30:44 -0400
From: "Jerry"
Subject: FW: [ATM] Another Astigmatism question, but at the sphere
stage
To: "ATM list"
Message-ID: <002b01c5ac41$ad72f0d0$0100a8c0@D85SJB21>
Content-Type: text/plain; charset=us-ascii
Look at the asymmetry in the two images on the page with the graphs.
Particularly image one shows it best. Do you see the squarness of the right
side of the number one image? The corner is at 3 o'clock. The shadow border
is somewhat square instead of round. The border of the shadow is nearly a
diagonal line on the upper right. It shows in number two also. Look at the
width of the shadow in the upper right compared to the lower right. It is
easy when you know what to look for. There are other signs in there. I only
point out the easiest to see.
Also there is surface roughness which seems to go with astigmatism. Or maybe
astigmatism goes with roughness. I have seen astigmatism on images posted on
the net and usually, in fact every one I've seen with a rough surface. Maybe
it is a result of working too vigorously and maybe too much weight for the
manner of support.
Then if you look at the numerous images a few show it. Also do you see the
hexagon shape of the central depression, just outside the little bump in the
middle?
Jerry
-----Original Message-----
From: Guy Brandenburg [mailto:gfbrandenburg@yahoo.com]
Sent: Sunday, August 28, 2005 7:22 PM
To: Jerry; 'James Lerch'; 'ATM'
Subject: RE: [ATM] Another Astigmatism question, but at the sphere stage
If you can see the astigmatism in those 2 knife-edge
images, you either have much better eyes, or a much
better imagination, than I do. Are you serious, Jerry?
Guy
--- Jerry wrote:
> Ok! Thanks James. And the astigmatism does show in
> those images.
> Jerry
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net
> [mailto:atm-bounces@atmlist.net] On Behalf Of
> James Lerch
> Sent: Sunday, August 28, 2005 7:02 PM
> To: ATM
> Subject: Re: [ATM] Another Astigmatism question, but
> at the sphere stage
>
> ----- Original Message -----
> From: "Jerry"
>
> >Can someone provide Foucault and Ronchi images of
> this astigmatic mirror?
>
> Jerry,
>
> I have archived 120+ unmasked Foucault images on
> mirror C, here:
>
> http://lerch.no-ip.com/atm/MRR/
>
> Click on Mirror C Results at the top, Section #3,
> sub-section 3 (Between the
>
> robo Foucault results and the interferometry
> results)
>
> BTW, each image is flawed by a small speck of dust
> some where in my CCD
> camera.
> The flaw shows up as a small 'blotch' in the bottom
> center of each image.
>
> Hopes this helps.
>
> Take Care,
> James Lerch
Guy Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
------------------------------
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ATM mailing list http://www.atmlist.net/
End of ATM Digest, Vol 20, Issue 33
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Start your day with Yahoo! - make it your home page
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