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24" Maksutov

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#1 Steve Dodds

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Posted 11 October 2019 - 03:56 PM

There are the blanks for a 24" maksutov over in the classifieds, corrector is slumped but still 2" thick, primary is 4" thick.  How long would this monster take to cool down?

Which one of you is insane to take this on?

 



#2 Augustus

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Posted 11 October 2019 - 03:59 PM

If finished, it would be among if not the largest ever built. The largest one I know of is the 22" Stamford Observatory Mak which had similar thickness optics.

 

8000th post


Edited by Augustus, 11 October 2019 - 04:54 PM.


#3 fcathell

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Posted 11 October 2019 - 04:42 PM

I think a monster like this would have be kept in an air conditioned/refrigerated room prior to use or it would never reach equilibrium in a reasonable amount of time. At 24 inches, I suspect there could also be some corrector "sag" when pointed at the zenith.

 

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#4 JohnH

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Posted 12 October 2019 - 08:35 PM

The largest in the world is a 600mm one in Crimea.

Edited by JohnH, 12 October 2019 - 08:36 PM.

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#5 Augustus

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Posted 12 October 2019 - 08:59 PM

The largest in the world is a 600mm one in Crimea.

Is that the corrector diameter or the primary? The Stamford one has a 25" primary and 22" corrector; this has a 24" primary and 23.25" corrector.



#6 JohnH

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Posted 12 October 2019 - 09:02 PM

Is that the corrector diameter or the primary? The Stamford one has a 25" primary and 22" corrector; this has a 24" primary and 23.25" corrector.


With the maksutov, while having zero power has considerable influence on spherical aberration needs a primary that is somewhat larger and the corrector to fully take advantage of the corrections available to it. I have no idea though with these really large ones what they actually measure the primary over the corrector

Edited by JohnH, 12 October 2019 - 09:04 PM.

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#7 BGRE

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Posted 12 October 2019 - 09:14 PM

Strictly the aperture is determined by the diameter of the stop which is usually located much closer to and in front of the meniscus corrector than the primary mirror.
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#8 Mike I. Jones

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Posted 12 October 2019 - 09:54 PM

I'd be wary about the glass homogeneity and strain in a piece that big.  Also, there's no mention of melt data, or what the glass even is.  It's likely something like BSC-2 or BK7, but without melt data and other characterization the project just poses too much risk.


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#9 luxo II

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Posted 13 October 2019 - 12:48 AM

If finished, it would be among if not the largest ever built

Maksutov completed a 70cm example which is in the Crimea.

It would be a heroic effort if you’ve never made one before. There’s also the mechanical challenge of the OTA and a suitable mount plus observatory and suitable location,

As a cassegrain it is somewhat pointless - the seeing will never be good enough to reach its resolution limit or make use of such a long focal length. Better to put a camera at the prime focus (with a flattener).

Edited by luxo II, 13 October 2019 - 12:57 AM.


#10 LarsMalmgren

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Posted 13 October 2019 - 04:52 AM

As a cassegrain it is somewhat pointless - the seeing will never be good enough to reach its resolution limit or make use of such a long focal length. Better to put a camera at the prime focus (with a flattener).

 

That statement is IMO just plain wrong today with modern cameras doing lucky imaging !

Such a large telescope would catch even more light to push exposure times further down and thus being able to catch those fleeting moments with excellent seeing.

A 600 mm aperture telescope have a Dawe's Limit of ~0.2 arc-sec.

 

Measure on the best planetary photographers images, ex. D. Peach's from Barbados.

He gets well below sub-arc-sec resolution with an 14" SCT.

And when he uses the 1 meter telescope in Chile it gets even better.

 

Even deep-sky uses shorter and shorter exposures.

Now 1-2 minute has replaced 10-20 minutes.

 

Sure, there are limits.  They're just not where they used to be because of the extremely good cameras we have today.

No, that statement cannot just be used as a blanket-statement shooting down big aperture anymore.

 

Just my 2 cents flowerred.gif



#11 totvos

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Posted 13 October 2019 - 08:52 AM

The subject of Maks came up in another conversation I was having, so this is timely. I don't know much (ok, anything) about the optics involved, but does the corrector need to be that thick? Can it be a thin meniscus (sub-1"), and if the primary is also a thin, fast, meniscus, this could be a cool project. What are the glass requirements for the corrector? I saw Bk7 mentioned above, but can it be made of, say, pyrex or even (gasp) plate glass?

 

And I was also thinking about the Maksutov camera concept in conjunction with this. In place of a field flattener, can a flexible image sensor be used? I know that they *exist* but am not sure if they are commercially available, or affordable.

 

https://www.telescop.../Mak-camera.htm



#12 JohnH

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Posted 13 October 2019 - 09:49 AM

Totvos, maksutov correctors work better the thicker they get but at a certain point you get a series of diminishing returns. The general rule of thumb is the thickness of the corrector is optimized at about one-tenth thickness in relation to its diameter so a 10-inch maksutov would normally have a 1 inch thick corrector

Edited by JohnH, 13 October 2019 - 09:50 AM.

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#13 tim53

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Posted 13 October 2019 - 01:34 PM

My 16" Mak Cass optical set has a 2" thick meniscus.  I do plan to air condition the observatory when I build it.  I can't imagine it reaching equillibrium during the night otherwise.

 

-Tim.


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#14 kur3tking

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Posted 13 October 2019 - 03:23 PM

I would be very careful about  a SLUMPED corrector. Although my company can slump glass from 9" R to 1000.00" R, and I am a huge Mak fan, I have never slumped a Mak corrector. Here is why.

 

In a conversation with Roland C. of Astro-Physics about Mak correctors, He said NOT to try and make a corrector from slumped glass. The corrector will not produce good star images and I understood that to mean regardless of how well it is slumped and annealed.  He is certainly more knowledgeable and experienced than I, so buyer beware!  This conversation was 10+ yrs. ago but I never bothered to slump a corrector despite the available time, oven access, glass availability, machine time, and desire.  My intent is NOT to open a can of worms but to pass on what I believe to be trustworthy information from a reliable source. That is the purpose of this forum?  Thanks to all for your time and attention.



#15 totvos

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Posted 13 October 2019 - 03:37 PM

I would be very careful about  a SLUMPED corrector. Although my company can slump glass from 9" R to 1000.00" R, and I am a huge Mak fan, I have never slumped a Mak corrector. Here is why.

 

In a conversation with Roland C. of Astro-Physics about Mak correctors, He said NOT to try and make a corrector from slumped glass. The corrector will not produce good star images and I understood that to mean regardless of how well it is slumped and annealed.  He is certainly more knowledgeable and experienced than I, so buyer beware!  This conversation was 10+ yrs. ago but I never bothered to slump a corrector despite the available time, oven access, glass availability, machine time, and desire.  My intent is NOT to open a can of worms but to pass on what I believe to be trustworthy information from a reliable source. That is the purpose of this forum?  Thanks to all for your time and attention.

Not a can of worms, but I would be interested to know *why*, not just because "he said so". Let's say it was perfectly annealed, with no strain. Would it still not work?


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#16 JohnH

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Posted 13 October 2019 - 03:38 PM

I would be very careful about a SLUMPED corrector. Although my company can slump glass from 9" R to 1000.00" R, and I am a huge Mak fan, I have never slumped a Mak corrector. Here is why.

In a conversation with Roland C. of Astro-Physics about Mak correctors, He said NOT to try and make a corrector from slumped glass. The corrector will not produce good star images and I understood that to mean regardless of how well it is slumped and annealed. He is certainly more knowledgeable and experienced than I, so buyer beware! This conversation was 10+ yrs. ago but I never bothered to slump a corrector despite the available time, oven access, glass availability, machine time, and desire. My intent is NOT to open a can of worms but to pass on what I believe to be trustworthy information from a reliable source. That is the purpose of this forum? Thanks to all for your time and attention.


Generating lens elements from slumped or pressed Glass has been industry standard for over a hundred years.


You think someone would have noticed that by now if this was the case that they produced inferior lens elements.
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