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Equipment Discussions >> ATM, Optics and DIY Forum

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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5743368 - 03/19/13 04:23 PM

Quote:

Made a Couder screen, tested it, 4 sets of measurements...overcorrected by 1/5.4 p-v.



Evaluated with a program, or with a calculator? How does the figure look when using FigureXP?

Quote:

Thanks all for the feedback. I was hoping that someone would say, "oh yeah, these 3 programs can't calculate pinstick setups...use paper and pencil only."



My experience shows that they work with pinsticks.....

Quote:

Obviously, I don't know how to put the numbers into XP correctly because of the discrepancy in the "ideal figures" column, yet got great wave shape. Screwed up on v2.0B, and ZONE.exe is wrong somehow.
Flummoxed.



I'd like to see the comparison of the Couder mask data to the pinstick data using FigureXP, and how all of that compares to your calculations.


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Dave O
sage
*****

Reged: 12/21/11

Loc: Sri Lanka
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5744277 - 03/19/13 11:33 PM

Quote:

"If they all agree to reasonable accuracy, I'd be suspicious of the star testing results."

Or the coater's 1/3 wave .73 strehl test? Will this ever end?




Perhaps you should have it tested by a different optician? If your testing indicates it is a good figure, I would not rush into changing anything until I was sure it needed changing (and what the necessary changes are).


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: Dave O]
      #5744829 - 03/20/13 10:34 AM

Yes. I'll sit on it for a while, more thinking than anything, and when I'm finally convinced, I'll act.

Supposed to be a hobby, not an obsession.


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5744969 - 03/20/13 11:51 AM

Quote:

Supposed to be a hobby, not an obsession.




yeah but an issue like this is one that really gnaws at you, or at least me.


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Norm Meyer
sage
*****

Reged: 02/08/09

Loc: Warren, ME 04864
Re: Caustic vs. Pinstick new [Re: Pinbout]
      #5745046 - 03/20/13 12:26 PM

That's why I like spherical systems when possible or
null testing. I guess I'm lazy.

Norm


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Caustic vs. Pinstick new [Re: Norm Meyer]
      #5745085 - 03/20/13 12:52 PM Attachment (6 downloads)

thats similar to autocollimation. no numbers.

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Tom Stokes
newbie


Reged: 03/19/13

Loc: Mission Viejo, CA
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5746254 - 03/20/13 08:52 PM

Scuse me. I joined CN in the last hour. Are you sure this isn't cockpit error? Why are the output numbers different from the input numbers? I ran the output numbers through my program Parab and got a Strehl of 0.99+ and a P-V of 1/76. I have never seen a better mirror.

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gregj888
professor emeritus


Reged: 03/26/06

Loc: Oregon
Re: Caustic vs. Pinstick new [Re: Tom Stokes]
      #5746539 - 03/20/13 10:56 PM

Sorry, dumb question. When you place the shadow, is it centered (equal brightness) on the pin or in the space between the pins?

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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: gregj888]
      #5747042 - 03/21/13 08:13 AM

Quote:

Sorry, dumb question. When you place the shadow, is it centered (equal brightness) on the pin or in the space between the pins?



The shadow crest...try to visualize the shadow shape as a 3-d donut curve... should appear to be just at the pin. The pin is, in effect, at the center of an equivalent mask aperture. This came up earlier when I was trying to convince myself that the pin location was also the "effective radius" of the zone, which is one of the software options when entering zone locations.

That means that you judge the mid-grey of the shadow as it crosses the pin. But, as I mentioned earlier, I get the same results if I measure from the first wisp of shadow crossing the pins, or the last hint of light in the shadow crossing the pin. As long as you use the same reference points for all measurements. In the photo of the mirror and pins, I'd say that the left pin is in the middle of the shadow region. The right shadow..hard to see because of the *BLEEP* photo..is not quite to the pin. This is probably a KE position of .002 too close to the mirror...wasn't meant to be a photo record of a KE setting, just an illustration.


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: Pinbout]
      #5747046 - 03/21/13 08:15 AM

Quote:

thats similar to autocollimation. no numbers.




I just love null testing. Or spheres.... That's a beauty of a Ronchigram, there, buddy.


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Ajohn
sage
*****

Reged: 12/03/07

Re: Caustic vs. Pinstick new [Re: gregj888]
      #5747071 - 03/21/13 08:35 AM

As I don't make mirrors very often I try checking a mirror several ways. One which can give good results is a mask with few holes in it ideally sized as per the caustic test suggestions in ATM. R/100 but larger works out too. Smaller may even be better. I have one central, one 70% and one near the edge. As the holes are small it's much easier to position the knife edge accurately and get the shadows moving exactly as they should do. One thing I find with coudre masks is that getting a really good central reading can be difficult. This goes back to my 1st mirror. I used several masks of a similar nature not entirely covering the mirror and found it much easier to do. When I finished that one I knocked up a Dall null test and couldn't see any errors at all. This was a 220mm F6 - wish I still had it.

Parab by the way is the only test software that allows people to work this way where the user dictates where the zones are. Others need dimensions of the mask or even dictate them. You might say what I do is a variation of makes sure zones are corrects and that the mirror is smooth between the ones that are chosen rather than completely cover the mirror with holes of one sort or another. I found that adequate for early figuring but hopeless at the end.

John
-


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747091 - 03/21/13 08:48 AM Attachment (5 downloads)

OKAY. Got my caustic rig up and running, ran 3 series of 3 measurements...different times of day with temps rising and falling in the lab a tiny bit.

I get 1/9.1 wave overcorrected.

Here's the numbers. I had to cheat because one of my mask apertures is slightly over the edge, so I called the mirror a 17.0" dia. to trick the software, which wouldn't let me enter a 1.25" dia hole at 7.5" radius.

Mirror R=142.7"
Hole dia. 1.25"
Z1 1.5"
Z2 3.0"
Z3 4.5"
Z4 6.0"
Z5 7.5"

Fixed source, adjustable slit to tune the diffraction effects around the wire.

I use a Mitutoyo Dial indicator reading in .0001". My X measurements are repeatable to about .001", so I'm working on accuracy, but the averages of 9 sets of numbers are:

Values are Y, X

Z1 .047, .0010
Z2 .186, .0048
Z3 .426, .0194
Z4 .757, .0435
Z5 1.183, .0838

I'll be doing more measurements and refine my technique, and maybe tweak my setup...as you can see, it's a bit crude. Caustic Tester sits on my Hendy lathe apron, on a piece of 12" SCH40 pipe. Mirror is seen through the aperture of my polishing room.


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747148 - 03/21/13 09:16 AM Attachment (4 downloads)

Sorry, X measurements are:
.0004
.0026
.0093
.0215
.0417


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747286 - 03/21/13 10:33 AM Attachment (3 downloads)

Parab by the way is the only test software that allows people to work this way where the user dictates where the zones are.
******
No, I find that the other programs allow different locations. Foucault analysis v2.0B, and Figure XP allow input. Or did you mean Couder? I'm not crazy about that setup, as I agree, finding the center radius seems just too "hazy". Maybe with practice, but there are a lot of moving shadows in the 6" hole. Probably make a mask with more zones, but this was the one that Foucault analysis v2.0B stated. I could throw a cat through the center aperture.


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747411 - 03/21/13 11:39 AM

you need to drive it to delmarva this weekend as a walkin, what is it $25 and have steve look at it in his rossnull.

you could pick me up on the way down.

but yeah you need another type of test other than KE or caustic to verify your results.

your going around in circles at the moment.

Edited by Pinbout (03/21/13 11:40 AM)


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: Pinbout]
      #5747430 - 03/21/13 11:48 AM Attachment (3 downloads)

Yeah, circles....

This screenshot is from entering values derived by r^2/2R.

Looks right. Nice figure, etc.


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747447 - 03/21/13 11:58 AM Attachment (3 downloads)

This one is from an entry where the only thing I changed was entering measurements that are supposedly targets for my figuring .070, .115, .159, .202, .226, .250.
As I figured it, the numbers approached these values, and the wavefront improved from 1/4 wave.

WHY did the program report different numbers?!!!

And a fine mirror.

These are about the same numbers I put into figure XP.

Why did that program ALSO report different numbers?!!!

Also a fine mirror.


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Caustic vs. Pinstick new [Re: Pinbout]
      #5747459 - 03/21/13 12:04 PM

Quote:

you need to drive it to delmarva this weekend as a walkin, what is it $25 and have steve look at it in his rossnull.




Hey! That's a good idea! Build a Rossnull! Another set of dimensions and measurements to question...

Going 'round the twist here...


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747674 - 03/21/13 01:46 PM

nobody said build it, go have him check it.

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gregj888
professor emeritus


Reged: 03/26/06

Loc: Oregon
Re: Caustic vs. Pinstick new [Re: ccaissie]
      #5747782 - 03/21/13 02:54 PM

Just checking...

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