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Equipment Discussions >> ATM, Optics and DIY Forum

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PrestonE
Carpal Tunnel
*****

Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Have a 12 inch Maksutov corrector...what to do?
      #5658435 - 02/02/13 04:19 PM

Hello Everyone,

Having purchased all sorts of optical glass over the years, and going through it to see what might make a nice next project I find a lovely fully finished 12 inch Maksutov corrector lens.

No details on the type of glass. I could measure the curves.

Would it be possible and is it worth the time to reverse design something from this lovely piece of glass

If so, what would be the best use and design?

There is no central perforation.

Thanks in advance for you kind ideas and suggestions.

Like I need another project, but it has been 4 years since finishing the 20" RC and we have very clear dark sky's here in this part of Mexico.

Very Best Regards,

Preston


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ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5658448 - 02/02/13 04:30 PM

If applying it to a Mak design, need accurate measurement on R1,R2 and the thickness. The glass type that was commonly used in the Mak club days was usually BSC-2, and someone from that era could provide the info on that. Sounds like a 14" Sphere is the mating R3 element.

Otherwise I can't guess it's usefulness. This is about the best place to post such a query.


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ed_turco
Pooh-Bah
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Reged: 08/29/09

Loc: Lincoln, RI
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: ccaissie]
      #5658635 - 02/02/13 06:04 PM

BSC2 had a refractive index of 1.517 and an Abbe Number (V) of 64.5. In optical parlance, it would have a number of 517645. Hope this helps.

Schott glass is listed as 517641, and frankly, that ain't much of a difference.


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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: ed_turco]
      #5658660 - 02/02/13 06:17 PM

A fast mak newt would complement the 20 RC nicely.... Would be interesting to see what could be reverse engineered outta that glass.....

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Mike I. Jones
Post Laureate
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Reged: 07/02/06

Loc: Fort Worth TX
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: gatorengineer]
      #5659256 - 02/03/13 01:37 AM

Hi Preston,
By all means measure the radii and central thickness, and clear apertures for R1 and R2 as well. The steepness of the curves will help narrow down whether to do a Mak-Newt, Mak-Cass, or even Mak-Gregorian, and if not a Newt, whether the secondary mirror can be a spot on R2, or has to be a separate optical element.

One thing to do early on is get a dummy shine on both sides and test for strain with crossed polarizing filters. If zero to very little color birefringence is observed, the blank is suitable for use in a telescope. If you see dazzling stress rainbows, Maltese crosses, etc., it should either be re-annealed by someone that has the right equipment, or set up for a few rounds of fun practice target shooting.

Mike


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PrestonE
Carpal Tunnel
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Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Mike I. Jones]
      #5659922 - 02/03/13 12:45 PM Attachment (39 downloads)

Thanks Guys,

This is the first time the lense has ever been totally unwrapped as far as I can remember.

Kindly check the following information below:

R1 radius 12.17 inches
R2 radius 12.703 inches
R1 clear diameter 11.9375 inches
R2 clear diameter 12.254 inches
Edge thickness .885 inches
center thickness .895
Hole diameter 2.996 inches

I did not know that it had a hole in the center

There is no strain at all

I purchased this lens in 2006 from a well known ATM in hopes of making a nice planetary scope.

Let's see what the best use will be and thanks in advance for your kind help and suggestions.

Very Best Regards,

Preston


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PrestonE
Carpal Tunnel
*****

Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5659924 - 02/03/13 12:46 PM Attachment (36 downloads)

And the top view.

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JohnH
Carpal Tunnel
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Reged: 10/04/05

Loc: Squamish BC Moved!!!!!
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5659965 - 02/03/13 01:09 PM

I would appear to be polished so you can o a strain test right off.

With the hole already drilled, it will be more difficult to do any more polishing or apherizing. This also suggests it was planned to have the secondary mounted separately. Cassegrain or Newtonian though is currently anyones guess.


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ed_turco
Pooh-Bah
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Reged: 08/29/09

Loc: Lincoln, RI
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: JohnH]
      #5660151 - 02/03/13 02:56 PM

I don't see that hole as much of a problem in polishing or figuring. You just use a pitch lap with a hole trimmed away to a diameter slightly larger than the hole diameter. Have done this many times.

You might get a turned up edge around that hole but that is so easy to correct.


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Have a 12 inch Maksutov corrector...what to do? new [Re: ed_turco]
      #5661351 - 02/04/13 09:29 AM

Quote:

I don't see that hole as much of a problem in polishing or figuring. You just use a pitch lap with a hole trimmed away to a diameter slightly larger than the hole diameter. Have done this many times.




I did a 6" f2 like this back in the 80's. Nobody told me I couldn't so I did it. I don't recall any issues at all.

dan


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Jeff B
Carpal Tunnel
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Reged: 12/30/06

Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5661380 - 02/04/13 09:45 AM

With the hole in the middle, it would make a really cool and trendy bathroom sink.

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Mike I. Jones
Post Laureate
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Reged: 07/02/06

Loc: Fort Worth TX
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Jeff B]
      #5661483 - 02/04/13 10:41 AM

Preston - I'm not coming up with anything (yet) that can use those radii without changing them and still have good optical performance. Can you test R1 to see if it's spherical, or if any aspherization has been done to it?

Not giving up, will post some results soon.
Mike


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PrestonE
Carpal Tunnel
*****

Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Mike I. Jones]
      #5661650 - 02/04/13 12:20 PM

Mike, I will have to dig around the ATM stuff to find the knife edge or Ronchi tester and set it up.

May be a couple of days as there are still 50 to 75 boxes that have yet to be up packed!!!!

Not near the space here as the 3 shops and attic in Houston use to have.

Best Regards,

Preston


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Ed Jones
Carpal Tunnel
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Reged: 04/06/04

Loc: Sin-sin-atti
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5661935 - 02/04/13 02:47 PM Attachment (29 downloads)

Preston,
My guess is that it is BK7 and I come up with this design. You could measure it's specific gravity to help identify it. The corrector R1 is aspherized as well as the secondary.


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PrestonE
Carpal Tunnel
*****

Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Ed Jones]
      #5662100 - 02/04/13 04:45 PM

Hi Ed,

I will source a container that I can do that with in the next few days and get that done.

How much aspherize will be needed on R1?

What is the final F ratio?

Will the primary need to be larger than the corrector?

Best Regards,

Preston


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Ed Jones
Carpal Tunnel
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Reged: 04/06/04

Loc: Sin-sin-atti
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5662186 - 02/04/13 05:37 PM

Preston,
Looks to me like ablout 7.6 fringes @.633 nm. The F ratio is f/10 and I think a 12.5 inch blank is what it was intended to be used with.

Ed


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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5663171 - 02/05/13 09:43 AM Attachment (25 downloads)

I'm guessing Preston's corrector is purely spherical, and probably very good spheres at that. Assuming spherical surfaces, I tried several configurations that did not require aspherization of R1 or R2. This design was particularly interesting: the unmodified, all-spherical, BSC-2 517645 shell matched with a weakly aspherized primary mirror and all-spherical BK7 Mangin gives very sharp spots. Light passes twice through both the corrector shell and Mangin. I've never seen a Mak shell used quite like this. The shell and primary mirror are mounted on the same spool that holds the primary baffle tube. I tried reversing the shell, and it wasn't as good as in this direction. The primary is figured with only about 6.5 waves departure from the nearest fit sphere. It's a weak higher order asphere, but you would just simply figure it from a sphere to give a double-pass system null, without realizing you're making an 8th or 10th order asphere. EFL is 122.8", f/10.4, field is 1/2" diameter.
Mike


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Ed Jones
Carpal Tunnel
*****

Reged: 04/06/04

Loc: Sin-sin-atti
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Mike I. Jones]
      #5663907 - 02/05/13 04:36 PM

That's totally unique Mike, very interesting!

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PrestonE
Carpal Tunnel
*****

Reged: 04/29/05

Loc: San Miguel de Allende,Mexico
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: Mike I. Jones]
      #5664059 - 02/05/13 05:51 PM

Now that is really thinking outside of the box

I really like this very different design a lot Mike.

What more do you need from me at this point

I will be digging around all the boxes in the next few days to try and discover just where all of the ATM goodies are including the testers.

Very Best Regards,

Preston


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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: Have a 12 inch Maksutov corrector...what to do? new [Re: PrestonE]
      #5664096 - 02/05/13 06:14 PM

Well, one thing for sure, if you build it you'd have the only one like that bubba on the block! Or in Mexico. Or Earth.

For any design you end up using, just confirm the radii values and sphericity, the hole ID to 0.001", and the thickness at the edge of the hole to 0.001" (so we can calculate what the center thickness would be). Also, get in contact with that "well known ATM" to see if he has working logs for it that document all the final dimensions.

I can put up the prescription now (it's too many surfaces for OSLO-EDU), and if your own measurements or the ATM fellow's data are different from what you said above, we can tweak the design to match.

Ed and/or I can hunt for a near-null test geometry for the separate corrector/primary assembly, and the Mangin by itself. Nice to reduce risk by getting good clean nulls on subassembly components before you put them together.

I'll also dimension the baffle tubes for you, once the design is frozen. You got good at makin' them conical baffles for sure.

It would be fun to see an unconventional wack-job design like this one built. Trying the corrector in that position was totally an experiment on my part, one I was surprised that worked so well.

Mike


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