54 replies to this topic

[Whiteduckwagglinginspace]

A simple question, just because I'm curious about it:

How big does (commercially made) aperture goes?

(I know about the 25 inch Obsession, but maybe there are suppliers who sell even bigger ones...)

[Shubham]

Refractors usually go up to at least 12”. NMT offers up to 50” dobs. ASA offers upto 2.5m RCs.

 

I’m sure at this level, the actual products are customized to fit the user’s requirements, but I’m sure these would still be considered “commercial” products despite the fact that they’re likely to be semi-COTS solutions than purely off the shelf products.

[Whiteduckwagglinginspace]

Refractors usually go up to at least 12”. NMT offers up to 50” dobs. ASA offers upto 2.5m RCs.

 

I’m sure at this level, the actual products are customized to fit the user’s requirements, but I’m sure these would still be considered “commercial” products despite the fact that they’re likely to be semi-COTS solutions than purely off the shelf products.

Thank you very much for telling this - even bigger than expected. Guess the price of a 2.5 m RC is quite out of reach for most of us. (from 7.270.000 dollar) Total weight:  17.000kg / 37.478lbs!

Edited by Whiteduckwagglinginspace, 17 June 2025 - 08:36 AM.

[NinePlanets]

This outfit has a lot of experience supplying big scopes:

 

https://www.dfmengin...com/cct_50.html

[TOMDEY]

In the truly large sizes they're custom builds. My New Moon scope is 36 inches with a Normand Fullum Techno-Fusion Primary Mirror. Where I worked (professional telescopes) our bread and butter was in the few meter class with a few much larger.    Tom

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[Whiteduckwagglinginspace]

In the truly large sizes they're custom builds. My New Moon scope is 36 inches with a Normand Fullum Techno-Fusion Primary Mirror. Where I worked (professional telescopes) our bread and butter was in the few meter class with a few much larger.    Tom

Must be a joy to look through that 36 incher! I can only imagine what that must look like.

[WadeH237]

Must be a joy to look through that 36 incher! I can only imagine what that must look like.

If you can get to a major star party, you might be able to find out for yourself.

 

Over the years, I've looked through two different 40" scopes, many scopes in the 25" to 30" range, and even a pair of "binoculars" that was built from two 22" scopes side-by-side.

[Starman1]

A simple question, just because I'm curious about it:

How big does (commercially made) aperture goes?

(I know about the 25 inch Obsession, but maybe there are suppliers who sell even bigger ones...)

You have some good answers.

The largest "portable" scope I've viewed through was a 36" brought to RTMC.

A 41" was brought to one star party but the mount broke on assembly and I didn't get to look through it.

I've viewed through several 32" scopes at star parties.

 

The thing to remember about these large scopes is that they all have long focal lengths.

A friend's 32" is very short for a 32", but still has a 2805mm focal length.

And most large scopes are much longer.

So fields of view are small and magnifications higher at the exit pupils you typically run into.

At the ubiquitous 2mm exit pupil, that short 32" has a 406x magnification.  In an 8" scope, it's only 102x.

[dustyc]

Fullum makes scopes up to 65". 

Has a 3 mirror system to keep the eyepiece height down to a reasonable level.  

[TOMDEY]

Must be a joy to look through that 36 incher! I can only imagine what that must look like.

It's like what a medium sized scope shows... but as if you are that close and then hold binoculars up to your eyes. So bright stars become almost blindingly bright and "little fuzzies" become "big fuzzies" loaded with structure. That... and it just ~feels different~ which is a qualitative feeling hard to describe buy differently distinctive. My illustration here sort of gives a feel for that experience >>>  Tom

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[A Star Geezer]

If you got the moola , like NASA does than 21 foot reflector. James Webb Telescope 

[Whiteduckwagglinginspace]

Fullum makes scopes up to 65". 

Has a 3 mirror system to keep the eyepiece height down to a reasonable level.  

That's a great thing, because observing on a ladder is far from comfortable. But also wondering if this method causes loss of light or other disadvantages... 

Edited by Whiteduckwagglinginspace, 17 June 2025 - 11:43 AM.

[Starman1]

That's a great thing, because observing on a ladder is far from comfortable. But also wondering if this method causes loss of light or other disadvantages... 

Think about it.  A 4-5% loss of light on 65 of aperture?

What % is 65" larger than your current scope?

Light loss doesn't matter.

Collimation and a large secondary are the main problems, not to mention the cost of a re-coat 10 years down the road.

[Dave Mitsky]

There's a photo of one of Normand Fullum's folded-Newtonian telescopes at https://www.optiques...com/telescopes/

[Dave Mitsky]

A photo of Jimi Lowrey's 48" f/4 Dob can be seen at https://adventuresin...ober Part I.htm

[Shubham]

I think at these large sizes, RC telescopes make much more sense than Newtonians.

[havasman]

I think at these large sizes, RC telescopes make much more sense than Newtonians.

All of the > 30" telescopes I am aware of are visual observing tools. That enterprise is better served by a Dob. And at lower cost too.

Edited by havasman, 17 June 2025 - 03:55 PM.

[Starman1]

There's a photo of one of Normand Fullum's folded-Newtonian telescopes at https://www.optiques...com/telescopes/

https://www.optiques.../photo-gallery/

Middle pic.

[Starman1]

A photo of Jimi Lowrey's 48" f/4 Dob can be seen at https://adventuresin...ober Part I.htm

More insane is the ladder he uses:

https://www.wildcard...barbarella1.gif

[Dave Mitsky]

https://www.optiques.../photo-gallery/

Middle pic.

That's the same photo as on the opening page at https://www.optiques...com/telescopes/ (Fullum-folded Newtonian telescopes)

Edited by Dave Mitsky, 17 June 2025 - 04:21 PM.

[Starman1]

I think at these large sizes, RC telescopes make much more sense than Newtonians.

Secondaries are too large a % of the aperture in RCs.  They make better astrographs.

[Starman1]

That's the same photo as on the opening page.

Yes, with other pics of his largest scopes.

[Shubham]

Secondaries are too large a % of the aperture in RCs.  They make better astrographs.

If we set aside the costs and assume a permanently installed setup, I’d doubt one would notice a significant difference between, for example, the 34% CO of ASA 800AZ f10 and a fast 32” dob. The focal lengths would differ significantly between the two but I’d much rather take comfortable, same height, seated observation with 34% CO in an RC than going up and down a ladder in dark. Not to mention the 800AZ would allow imaging and research applications as well, compared to a purely visual use of the dob.

[Keith Rivich]

That's a great thing, because observing on a ladder is far from comfortable. But also wondering if this method causes loss of light or other disadvantages... 

I have to disagree with this. A proper ladder for the scope can be quite comfortable to observe with. Matched properly there are no bad viewing positions.

[Jon Isaacs]

If we set aside the costs and assume a permanently installed setup, I’d doubt one would notice a significant difference between, for example, the 34% CO of ASA 800AZ f10 and a fast 32” dob. The focal lengths would differ significantly between the two but I’d much rather take comfortable, same height, seated observation with 34% CO in an RC than going up and down a ladder in dark. Not to mention the 800AZ would allow imaging and research applications as well, compared to a purely visual use of the dob.

 

Exactly what mount is it where the eyepiece doesn't change height and angle? Even with a short focal length refractor, the seat height changes significantly..

 

Cost and transportability are important factors.. many/most of amateur astronomers travel to observe under dark skies...

 

Jon