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Equipment Discussions >> ATM, Optics and DIY Forum

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Napersky
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Reged: 01/27/10

Loc: Chicagoland
Stellafane Mirror Test Stand
      #5616013 - 01/10/13 06:25 PM Attachment (83 downloads)

My completed Stellafane mirror test stand for my new 15" flat.

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Napersky
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Reged: 01/27/10

Loc: Chicagoland
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5616016 - 01/10/13 06:27 PM Attachment (45 downloads)

Before the angle supports are cut.

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Napersky
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Reged: 01/27/10

Loc: Chicagoland
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5616018 - 01/10/13 06:29 PM Attachment (35 downloads)

Assembled before glueing.

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Napersky
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Reged: 01/27/10

Loc: Chicagoland
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5616020 - 01/10/13 06:31 PM Attachment (42 downloads)

Mostlu completed missing the top supporting rubber grommet.

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5616927 - 01/11/13 09:45 AM

Mark,
If your going to use the flat for autocollimation testing, beside the up/down tilt adjustment screw on the back you'll need a method to adjust the tilt from side to side.

- Dave


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kfrederick
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Reged: 02/01/08

Re: Stellafane Mirror Test Stand new [Re: DAVIDG]
      #5616956 - 01/11/13 10:06 AM

That flat would make a great"Fundy" telescope fixed eyepiece The planet is the mounting .Could also try EDs window Chief idea . Nice setup Maybe you could start a "Rent A Flat"

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Pinbout
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Reged: 02/22/10

Loc: nj
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5616963 - 01/11/13 10:13 AM

I ripped of Mr. Parkers AC to make a non perf AC.



still on the list of things to do...


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Napersky
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Reged: 01/27/10

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Re: Stellafane Mirror Test Stand new [Re: DAVIDG]
      #5616981 - 01/11/13 10:27 AM

Quote:

Mark,
If your going to use the flat for autocollimation testing, beside the up/down tilt adjustment screw on the back you'll need a method to adjust the tilt from side to side.

- Dave




Dave,

I have on the front of the tester two adjustible feet to move one up and the other down. Also from what I've read on the instructions for side to side I can just move the whole stand.

Mark


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Napersky
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Re: Stellafane Mirror Test Stand new [Re: Pinbout]
      #5616984 - 01/11/13 10:30 AM

Quote:

I ripped of Mr. Parkers AC to make a non perf AC.



still on the list of things to do...





Now that is cool. Also has the swivel for DavidG's "side to side" comment!


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DAVIDG
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Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5617193 - 01/11/13 12:30 PM

Mark,
Trust me you'll need a way to precisely move the flat in both axis to get it aligned. Those rubber feet will grab and then let lose and you over shot and also get the up/ down alignement out of wack. Two adjustments screws for both direction will make life much easier. If the flat isn't aligned correctly, you see astgmastism which causes the Ronchi lines and interference fringes to bow which makes it difficult to determine if the errors are in the optics your testing or coming from alignment issues.
Dick Parker's portable setup is very well engineered. It takes about 30 seconds to get the alignment dead perfect since you can easily do tip/tilt and side to side adjustmenst using two threaded rods.

- Dave


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Gary Fuchs
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Reged: 05/22/06

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Re: Stellafane Mirror Test Stand new [Re: DAVIDG]
      #5617270 - 01/11/13 01:17 PM

Here are some views of Dick's tester.





The extra threaded rods (on the left below) allow the mirror stand to be adjusted at longer distances.




For your setup you probably could have the tip/swivel controls on the inside and reach them from your viewing position.

I found what Dave G. described to be the case. If you don't have some sort of fine adjust for the swivel at least do something like a pin in the middle underneath and smooth bearing surfaces so you can push it smoothly to adjust.

The diagonal needs fine adjustability too...

Gary


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kfrederick
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Reged: 02/01/08

Re: Stellafane Mirror Test Stand new [Re: Gary Fuchs]
      #5617292 - 01/11/13 01:33 PM

Would not a Testing at the RC be more sensitive ??. I know it is a null test .Great test . Just ASKING a faint zone would the knife edge at RC be better to see?? You would know the zone was only on the mirror at the RC . Love to use the test only asking .

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Pinbout
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Reged: 02/22/10

Loc: nj
Re: Stellafane Mirror Test Stand new [Re: kfrederick]
      #5617307 - 01/11/13 01:44 PM

the AC doubles your error so they look twice as bad, but I heard Swayze say RoC is more sensitive.

You know that's a good reason to have the 3 test in your back pocket, to verify each other and rule out uncertainty, the KE, Ross-Null and AC.

the AC is so immediate with feedback, just opposite from what I'm use to so it can be disorienting.


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Gary Fuchs
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Reged: 05/22/06

Loc: Easton, PA, USA
Re: Stellafane Mirror Test Stand new [Re: kfrederick]
      #5617321 - 01/11/13 01:53 PM

Quote:

You would know the zone was only on the mirror at the RC .




My guess would be that the AC flat (or Ross lens) can't introduce a zone; but I'd like to hear a definitive answer.

Gary


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MKV
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Reged: 01/20/11

Re: Stellafane Mirror Test Stand new [Re: Gary Fuchs]
      #5617923 - 01/11/13 08:11 PM

Quote:

Quote:

You would know the zone was only on the mirror at the RC .




My guess would be that the AC flat (or Ross lens) can't introduce a zone; but I'd like to hear a definitive answer.

Gary



AC flats can depart from flatness by many waves, but their surface finish must be impeccably smooth. One way to check if the zone is introduced by the flat is to rotate the mirror. If the zone remains unchanged in the same location on the wavefront, then it must originate in the flat.


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Napersky
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Re: Stellafane Mirror Test Stand new [Re: MKV]
      #5619357 - 01/12/13 04:09 PM

Dave,

I need a mirror test stand for my interferometry. I do like Dick's mirror stand. I wonder does he have specific measurments and plans available such as for the Stellafane test stand I built?

Thanks,

Mark


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DAVIDG
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Loc: Hockessin, De
Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5619404 - 01/12/13 04:37 PM

Mark,
I understand that you need the stand to hold your flat for interferometry, but the setup to test a mirror or lens using a flat and your interferometer is exactly the same as autocollimation just instead of using a Foucault/Ronchi tester it will be replaced with your interferomter. So your going to need to able adjust things with the same or better precision as what we do when doing autocollimation since you'll be looking at fringes.
I don't know if Dick has set of plans available.

- Dave


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MKV
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Reged: 01/20/11

Re: Stellafane Mirror Test Stand new [Re: Gary Fuchs]
      #5620136 - 01/13/13 02:24 AM

Quote:

My guess would be that the AC flat (or Ross lens) can't introduce a zone; but I'd like to hear a definitive answer.



Gary, you are not looking at any optical surfaces but at a returning wavefront, whose quality is a sum-total of all the errors/deformations caused by individual optical components.

It stands to reason that a small, say, 1/30 wave valley on the flat will reflect off of it as a 1/15 wave local deformity on the wavefront and that it should be visible to an observer as a "zone".

Mladen


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Pinbout
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Reged: 02/22/10

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Re: Stellafane Mirror Test Stand new [Re: Napersky]
      #5620350 - 01/13/13 09:29 AM

Quote:

I wonder does he have specific measurments and plans available




I did another model more like his, the threaded rod ends in the dowel nuts so the stand can rotate as the screw is turned.



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Gary Fuchs
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Reged: 05/22/06

Loc: Easton, PA, USA
Re: Stellafane Mirror Test Stand new [Re: MKV]
      #5620547 - 01/13/13 11:18 AM

Quote:

Quote:

My guess would be that the AC flat (or Ross lens) can't introduce a zone; but I'd like to hear a definitive answer.



Gary, you are not looking at any optical surfaces but at a returning wavefront, whose quality is a sum-total of all the errors/deformations caused by individual optical components.

It stands to reason that a small, say, 1/30 wave valley on the flat will reflect off of it as a 1/15 wave local deformity on the wavefront and that it should be visible to an observer as a "zone".

Mladen




Thanks Mladen,

I'm in over my head so please bear with me; I'm thinking of a "zone" as an annular region of the mirror; and having trouble understanding how, say that valley on the flat, could cause a zone to show up if it wasn't there in the first place.

Gary


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