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Equipment Discussions >> ATM, Optics and DIY Forum

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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 (400 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 (260 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 (225 downloads)

and the photoshop pic

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


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ed_turco
Pooh-Bah
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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
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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
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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
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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 (152 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
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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 (110 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
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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
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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
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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
Carpal Tunnel
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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
sage
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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
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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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JohnH
Carpal Tunnel
****

Reged: 10/04/05

Loc: Squamish BC Moved!!!!!
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Gord]
      #5663273 - 02/05/13 10:22 AM

This is a variation of the "Solid Cat" Vivitar 800mm f/11 which used the same principle, except a larger scale.

Its advantage was it would never fall out of collimation, not without a force large enough to shatter the glass or metal housing.


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Stipe Vladova
super member


Reged: 10/08/10

Loc: Split, Croatia
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5663297 - 02/05/13 10:33 AM

Take some photos thru the scope!

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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: JohnH]
      #5663717 - 02/05/13 02:54 PM Attachment (96 downloads)

Thanks all for your enthusiasm!

Gord, it actually fits INSIDE an eyepiece and it might be used as a finder. The field of view is limited however, so it will not make a perfect finder. For that purpose a larger diameter would be required.

John, thanks for this this interesting comment! I didn't know this Vivitar lens so after some googling I found that the optical configuration of the Vivitar consists of several (bonded) components with different refractive indices and with some air gaps. For comparison below the layout of the 30mm Solid SCT which is made from just one piece of BK7, no bonding whatsoever...
The baffles are not displayed in the plot.

Vladova, hopefully I can do some 'astronomical imaging' during the next weekend!
If I have something to show I'll post it here.


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ahopp
sage


Reged: 05/24/12

Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5663785 - 02/05/13 03:33 PM

When I said earlier that "I want one" I was not just saying it:

"I WANT ONE, please'

Tony


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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: ahopp]
      #5663808 - 02/05/13 03:47 PM

Sorry Tony! So you're actually asking me to make one for you? Ehh.... I'm very flattered! Let me think about it for a while, and I'll answer you by PM. Is that ok for you?

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ahopp
sage


Reged: 05/24/12

Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5664404 - 02/05/13 10:04 PM

Quote:

Sorry Tony! So you're actually asking me to make one for you? Ehh.... I'm very flattered! Let me think about it for a while, and I'll answer you by PM. Is that ok for you?




Yes, contact me via PM, very interested in what you have done.

Tony


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StarStuff1
Post Laureate
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Reged: 04/01/07

Loc: South of the Mason-Dixon Line
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: ahopp]
      #5664492 - 02/05/13 11:31 PM

At first I thought there was a typo and the title should have said "A SOLID 300mm....."

Wow!

Barry Crist of b. crist miniatures could probably make you an appropriate sized mount and tripod.


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: StarStuff1]
      #5664635 - 02/06/13 03:40 AM

Quote:

Barry Crist of b. crist miniatures could probably make you an appropriate sized mount and tripod.




Actual working 1:10 scale model of a 12" f/10 Meade LX200 SCT, with GOTO and Superwedge...




Clear skies!
Thomas, Denmark


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Darenwh
Carpal Tunnel


Reged: 05/11/06

Loc: Covington, GA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Astrojensen]
      #5664787 - 02/06/13 08:19 AM

Well, I think I can stop coming to the ATM thread now. I don't think anybody's going to top this one. Great job...

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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: Darenwh]
      #5665383 - 02/06/13 02:22 PM

@ Vladova, well, I just discovered a very practical problem: The BFL of the little scope is too short to be able to focus with my DBK21 camera. I could make images at shorter distances however, so whenever I have something to show I'll post it here....

@ Thomas, I agree, it should have goto! Always easy when observing faint distant galaxies ;-)

@ Daren, Many thanks! But.... there are so many creative telescope makers out there, making incredible instruments in all kinds of types, dimensions and quality, I wouldn't stop visiting the ATM threads!


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maroubra_boy
professor emeritus


Reged: 09/08/09

Loc: Sydney, Australia
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: GlennLeDrew]
      #5665634 - 02/06/13 04:43 PM

Quote:

Bloody awesome!




Just what Glenn said!



And I thought my C5 was cute - stand aside C5, there's a new kid on the block

Alex.


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tim53
Postmaster
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Reged: 12/17/04

Loc: Highland Park, CA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: maroubra_boy]
      #5665667 - 02/06/13 05:04 PM

This is neat. What is the actual size of the focal plane. Many machine vision cameras have ccds on the order of 1/4" diagonally. If your focal plane is about that big, it might not make a bad e-finder at all! Just make a C-mount thread for it to screw right on the front of the camera.

-Tim.


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: rik ter horst]
      #5666676 - 02/07/13 09:10 AM

If you look through it backwards, does it work as a magnifier?

I agree with everyone, this is AWESOME! Just the right size for Barbie and Ken.


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ZeroID
sage


Reged: 04/21/10

Loc: Auckland, New Zealand
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Dick Jacobson]
      #5667676 - 02/07/13 07:07 PM

And I thought the Hubble scope was clever .... !!
Amazing work.


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kw6562
Authoritative Ignoramus
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Reged: 06/25/08

Loc: MA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: ZeroID]
      #5668202 - 02/08/13 12:42 AM

That is such a cool idea! Great job!

It reminds me of some catadioptric microscope objectives that I bought for a project at work a few years ago: Newport objectives

--Keith


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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: kw6562]
      #5670946 - 02/09/13 03:55 PM

Thank you all!
@Tim, in the first solid cas (shown here) a 1/4 inch ccd could be used although it suffers from field curvature. I've made a new design not so long ago which has a flat useful focal plane of at least 8 x 8 mm and a larger back focal distance. I hope to be able to make it soon.
@Dick, when using it backwards the obstruction makes it kind of useless unfortunately. What is possible however is to use it as a long distance microscope, from 1 meter distance and further....
@Keith, yes you're right, the dimensions are quite comparable. Optically it is a different story, but the microscope objectives you mention are interesting indeed!

Maybe we should ask Barbie and Ken what eyepieces they prefer.
Anyone out there wanting to make a 1.3 mm Ethos?? :-)


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: A SOLID 30 mm F/10 Schmidt Cassegrain new [Re: Gord]
      #5671152 - 02/09/13 06:18 PM

I'm beside myself. I thought for sure your 30mm was a typo for 300mm. Awesome, kudos and all that.

Pete


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