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Foucalt Mask, Software, Spider Color?

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#1 SteveV

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Posted 01 August 2020 - 09:18 PM

Searched CN and used google to find archived thinking on many questions but these are less definitive than I can determine.  Would appreciate some comments if anyone is inclined.

 

1.  I'm reading David Harbour Understanding Foucault for mind expansion.  Read these back when, will relook at Tex, Brown, Ingalls, Thompson.  Harbour suggests using a modification of Everest's stick pins vs the Couder mask for Foucault testing.  I'll be using a fixed source knife edge for testing if that matters in the choice of mask and I don't intend use digital images to assess the surface.  Question is: Is there a preferred mask for manual assessment of a mirrors surface?  What do you like?

 

2.  I have a 8" f/6 Dob built a long time ago with a with Zerodur (IIRC) mirror purchased directly from Discovery.  It has made it's way back home.  The original spider is a curved affair which is going to be replaced with a stainless steel 4 vane spider.  Question is: Do I leave the spider native shine, buff it up or paint it?  If so what color?

 

3.  Software suggestions for fixed source manual analysis of Foucault readings would be great.  I can't seem to run the old DOS programs, Tex, etc.  Any suggestions are welcome.  I'll build a spread sheet if needed but a canned program would be cool.  Don't mind paying for good work.  Question is;  Are there any new programs for manual analysis of Foucault readings, with fixed source?

 

Thank you for your time and thoughts.  Even if you don't respond that's fine there is lots of good reading here.



#2 mark cowan

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Posted 01 August 2020 - 09:30 PM

Don't use fixed source for testing unless you have a slow mirror, it's not necessary and introduces error unless the data is processed by SixTests analysis.  Moving source slitless tester is easier to build and works better.

 

FigureXP is available and works fine but the math is incorrect for fixed source.  It is correct for moving source.

 

No paint for spiders, bare metal is best.


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#3 SteveV

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Posted 01 August 2020 - 11:46 PM

Thank you.  I get the slitless vs slit thing.  Since I am going to build a new tester spent two weeks remaking and fooling around with the old tester to check the slitless out specifically because of discussions here.  It works fine but I find fixed source easier to get contrasty images, sneak up and null zones.  The 2X makes a difference.  I think it has something to do with ham, fists, sausage and fingers.

 

Thanks again.  I learn a lot reading here.  


Edited by SteveV, Yesterday, 10:15 AM.


#4 Dale Eason

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Posted Yesterday, 12:16 AM

It depends on if the spider can reflect light above and behind you into the focuser.  Mine can.  I painted mine flat black after I discovered that.



#5 SteveV

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Posted Yesterday, 12:22 AM

 Good point.  I'll check when it's mounted.  I suspect some surfaces likely will reflect light into the focuser.  Thank you,



#6 SteveV

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Posted Yesterday, 12:19 PM

 Does anyone have a preference between Everest Stick Pin as Harbour suggests or  Couder Masks?  TIA



#7 Pinbout

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Posted Yesterday, 12:33 PM

i make my own masks...couder and rona... ha ha ha

 

https://www.youtube....W8rBwA&index=25

 

all you do is divide the discs into equal areas... enter those rads into xp and your good.

 

143F65E9-1CF4-4A53-BFC5-BA9158ED5E22.jpeg


Edited by Pinbout, Yesterday, 12:37 PM.

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#8 mark cowan

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Posted Yesterday, 01:37 PM

Thank you.  I get the slitless vs slit thing.  Since I am going to build a new tester spent two weeks remaking and fooling around with the old tester to check the slitless out specifically because of discussions here.  It works fine but I find fixed source easier to get contrasty images, sneak up and null zones.  The 2X makes a difference.  I think it has something to do with ham, fists, sausage and fingers.

 

Thanks again.  I learn a lot reading here.  

 

That can all be adjusted by adding a bit of tape to the light source for the slitless to narrow it down.  Contrast is inherently the same.



#9 SteveV

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Posted Yesterday, 02:21 PM

Pinbout: I take it Couder is preferred then, but more stylish now than in the books!  

 

mark: I'll fool around with slitless some more before I build the new one.  I see Harbour uses a KE to form a slit in Design I, like the tape you mention.  Trying different apertures and diffusion screens didn't really do much for me, I'm sure it's my doing and not the principle.  Slitting the slit-less it is then.  

 

Thank you again.  




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