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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
A SOLID 30 mm F/10 Schmidt Cassegrain
      #5661318 - 02/04/13 09:05 AM Attachment (405 downloads)

About fifteen years ago I wanted to make a very small Schmidt-Cassegrain out of one solid piece of BK7, just to see if it could be done. So it became a 30 mm F/10 instrument, just small enough to fit ín an eyepiece! Thought it would be nice to share here...

Here's what I did:
I drilled a cylinder of 30 mm diameter and made one end convex spherical (the primary mirror) and the other end flat (the corrector side). In this side a small concave sphere was made, being the secondary mirror.
I calculated the needed aphericity of the Schmidt-corrector (21 microns!),ground and polished this deformation into the surface and made corrections using flexible polishing tools. In the middle of the spherical primary I made a concave sphere to bring the focus far enough outside the 'telescope' to be used in combination with a CCD or eyepiece. To prevent straylight I drilled cylinders around the secondary and into the primary mirror acting as light baffles. Then the mirrors were coated with aluminum. Although it was meant to be used ínside an eyepiece I never actually made a barrel where it could fit in. However, I have made two larger ones, with 40 mm diameter and I kept this little one as a nice memory.... Unfortunately I have no pics of these large ones.

The pictures below show you the size compared with an 1 1/4 inch eyepiece and I did some Photoshop to give you a realistic idea of what it would have looked like ;-)

Thanks for watching!

Cheers
Rik


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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5661320 - 02/04/13 09:05 AM Attachment (262 downloads)

Here's another one

Edited by rik ter horst (02/04/13 09:06 AM)


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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5661321 - 02/04/13 09:06 AM Attachment (227 downloads)

and the photoshop pic

Edited by rik ter horst (02/04/13 09:07 AM)


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ed_turco
Pooh-Bah
*****

Reged: 08/29/09

Loc: Lincoln, RI
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5661417 - 02/04/13 10:07 AM

OH MY GOSH!!! Some folks have incredible talents and you surely are one of them. I could never even imagine your device, never mind build it.

Congratulations!


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highfnum
Carpal Tunnel
*****

Reged: 09/06/06

Loc: NE USA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: ed_turco]
      #5661433 - 02/04/13 10:15 AM

one of a kind
does it work ?
what is pct central obstruction?

so cute!


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lukasik
Carpal Tunnel
*****

Reged: 10/11/05

Loc: Lawrenceville, Georgia
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: highfnum]
      #5661471 - 02/04/13 10:39 AM

Rik,

that is one of the coolest things I've ever seen - Outstanding!!!

Best Regards,

Bob


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: lukasik]
      #5661500 - 02/04/13 10:48 AM

Bloody awesome!

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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: GlennLeDrew]
      #5661543 - 02/04/13 11:10 AM Attachment (154 downloads)

Thanks a lot!
It does work within its limitations: Field is rather small, 10 mm diameter and it is curved. Linear obstruction is about 40%, and color correction is surprisingly good. Below the spot diagrams of the design.


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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: GlennLeDrew]
      #5661546 - 02/04/13 11:11 AM

Now that would put an end to tube currents, some thin' fierce!

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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5661550 - 02/04/13 11:13 AM Attachment (112 downloads)

When made a bit longer, you could obtain better color correction and a slightly flatter field, but then it wouldn't fit in an eyepiece anymore ;-)
Small right?


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siriusandthepup
sage
*****

Reged: 02/14/06

Loc: Central Texas, USA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5661781 - 02/04/13 01:28 PM

ooooo - I want one!

That is a telescope junkie piece if ever I saw one.

How does it do on the moon?


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Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: siriusandthepup]
      #5661801 - 02/04/13 01:40 PM

Words fail to describe how insanely awesome this is! A 30mm f/10 telescope that could fit inside a 10mm eyepiece, making a 30mm scope with 30x magnification and around 1.5° field.

If you made it a Gregorian Maksutov instead, it would have an erect image! It would also be slightly longer.


Clear skies!
Thomas, Denmark


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ASTERON
Carpal Tunnel
*****

Reged: 11/24/07

Loc: ISRAEL
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Astrojensen]
      #5661888 - 02/04/13 02:20 PM

Very out of the box thinking, pretty cool !
I love it !
How fast does it cool down ?
What Glass is it made off ?
Thanks for sharing


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rik ter horst
sage


Reged: 11/01/10

Loc: Ewer, the Netherlands
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: ASTERON]
      #5661957 - 02/04/13 03:08 PM

Thank you all for your kind words!

Asteron, cool down isn't an issue, unless you cool it to cryogenic temperatures in a really short time :-)
Material is 'ordinary' BK7, surface accuracy of the mirror surfaces was tested with polished spheres. Even at this scale, coma correction was done by aspherizing the secondary. By examining the fringe pattern on the test sphere you could see the aphericity easily.

Ed, I''ll make an image of the moon with it as soon as I get this thing in front of my camera...


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TVG
member


Reged: 05/03/12

Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5662011 - 02/04/13 03:37 PM

Very cool! I want one for my key chain.
Now you can just scale everything up from millimeters to inches.

Todd


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zjc26138
Loved By All
*****

Reged: 02/24/05

Loc: Mingo Junction, Ohio
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: TVG]
      #5662252 - 02/04/13 06:22 PM

That's pretty cool and a great idea!

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ahopp
sage


Reged: 05/24/12

Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: zjc26138]
      #5662403 - 02/04/13 08:06 PM

I want one please.

Tony


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Datapanic
Post Laureate
*****

Reged: 10/17/09

Loc: Tucson, Arizona
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: ahopp]
      #5662818 - 02/05/13 01:27 AM

Can't wait to see the mount! Hopefully, it's a fork equitorial with motor drives on both axis and setting circles. Very Nice X5!

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meade4ever
professor emeritus
*****

Reged: 08/23/07

Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Datapanic]
      #5663031 - 02/05/13 08:13 AM

Incroyable

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Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: meade4ever]
      #5663131 - 02/05/13 09:20 AM

Hmmmm... could you attach an EP to the end and use it as a finder? It is *way* cool!

Clear skies,


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