Author Topic: Building a Foucault tester.  (Read 283 times)

coreanoguf

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Building a Foucault tester.
« on: December 25, 2017, 02:22:15 PM »
I will facilitate my was into ATMing and thought I'd construct a Foucault tester.

The principle of the Foucault and the Ronchi I more or less grip, but I had some interest in attaching a camera to it.  Can somebody clarify the features of a lens/camera combo that would work well for all these testers?  Some I see use a DSLR, some use a webcam, some appear to utilize just a tiny telescope that they made.  Quite frequently I see it stated to post a picture of the evaluation to accompany questions, so I would incorporate it from the start.

This will be a good opportunity to utilize some various aluminum extrusions and random hardware I have been saving through time.  Although I am not adverse to using some timber parts too when it comes down to it.
In this pile are various kinds of digital measuring apparatus, hopefully one of them will be appropriate.
I'd like to construct a Foucault/Ronchi combo very similar to this video that Pinbout posted of the "Swayze" kind tester.

Any other hints would be appreciated also.

Oh, one more thing, are Teflon surfaces absolutely vital?  I am not against it, just I would have to get a thing and was wondering if these furniture feet items would be sufficient for the sliding surfaces.



facwindpsychco

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Re: Building a Foucault tester.
« Reply #1 on: December 29, 2017, 06:01:55 PM »
Quote
Oh ya, one more thing, are Teflon surfaces absolutely necessary?

you mean for the moving bed? it helps.

here's one with a cell and a 8x tele lens the cell attaches to. the wood clamps around the lens and a piece of 1/4" foamcore press fits onto the lens with the led and screen or ke taped to it.

I sit this on top of the stellafane base. [not shown]

reaipasjime

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Re: Building a Foucault tester.
« Reply #2 on: December 29, 2017, 11:21:09 PM »
here's an older version of a webcam attached to a camera lens.

I actually have a smaller Swayze thing attached to the front of the pedal lens hood.

https://www.youtube....h?v=Rs1ytxS8MAo

Chaudhari Evans

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Re: Building a Foucault tester.
« Reply #3 on: December 31, 2017, 01:49:45 AM »
Quote
<p class="citation">Quote

Oh ya, one more thing, are Teflon surfaces absolutely necessary?

you mean for the moving bed? it helps.

here's one with a cell and a 8x tele lens the cell attaches to. the wood clamps around the lens and a piece of 1/4" foamcore press fits onto the lens with the led and screen or ke taped to it.

I sit this on top of the stellafane base. [not shown][/quote]

Yes for the bed, example I have a short length of solid aluminum rod with a V-groove extrusion that might fit together nicely for the Y axis tippy linear bearing part. I will see what I can find, not a big deal I don't have to built it that way for any reason.

Hey that cell probably works well, a all in one capture view and in one device. Hmmm I've got one of those GoPros with a back LCD that never sees any "action" lol, maybe I will see if I can put that to use. Another option would be a 8" tablet I have.

So I guess it's fairly safe to say that the lens selection probably isn't to critical as long as it doesn't distort the image. Did you find the zoom of the camera lens setup to be preferred to the fixed 8x on the cell?

coepupinsynch

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Re: Building a Foucault tester.
« Reply #4 on: January 01, 2018, 07:00:26 AM »
A spare focuser makes a great tester.




Chris Goldsby

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Re: Building a Foucault tester.
« Reply #5 on: January 04, 2018, 06:15:33 PM »
That is a pretty compact device you made there.

I guess the X-axes side to side adjustments are made buy either tipping the razor blade or moving the whole device, base and all?

David Johnson

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Re: Building a Foucault tester.
« Reply #6 on: January 08, 2018, 06:24:32 PM »
Yeah the brass nob on the left is sitting on a ball bearing so when turned the knife edge moves across the mirror.

Ryan Fletcher

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Re: Building a Foucault tester.
« Reply #7 on: January 10, 2018, 08:35:37 AM »
That setup looks like it would have a lot of parallax especially in faster mirrors. This Ideally you want your return beam as close to the light source as possible to avoid that.

Mladen

leypelepha

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Re: Building a Foucault tester.
« Reply #8 on: January 11, 2018, 03:34:15 AM »
Quote
That setup looks like it would have a lot of parallax especially in faster mirrors. This Ideally you want your return beam as close to the light source as possible to avoid that.

Mladen

I don't look through the focuser, the return beam comes back just below the LED. The focuser is just there for a convenient movement device.

raposttavers

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Re: Building a Foucault tester.
« Reply #9 on: January 11, 2018, 04:52:51 PM »
Okay, I see it now, thank you.

Mladen

piesilila

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Re: Building a Foucault tester.
« Reply #10 on: January 13, 2018, 04:30:29 AM »
Quote
Yeah the brass nob on the left is sitting on a ball bearing so when turned the knife edge moves across the mirror.

I think I see it, the one in the aluminum circle in the second picture.

At first I though it was the brass knob on the red gear, maybe it is?

Donnell Keown

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Re: Building a Foucault tester.
« Reply #11 on: January 13, 2018, 11:26:30 AM »
It's the one on the red gear. It raises or lowers the left hand side.

retaweawebs

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Re: Building a Foucault tester.
« Reply #12 on: January 13, 2018, 07:29:51 PM »
OK, I get it, thanks.

Ryan Hernandez

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Re: Building a Foucault tester.
« Reply #13 on: January 31, 2018, 12:54:16 AM »
Pretty sweet tester

adlaycomsu

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Re: Building a Foucault tester.
« Reply #14 on: January 31, 2018, 07:23:15 AM »
Somewhere, there's an engine missing its flexplate

allan