You want a big scope?

[xelasnave]

Should be an easy build.

https://youtu.be/yAfUBiWOjNc

Alex

[Outcast]

That's nuts!!

[barx1963]

OHS issues not a problem!!:P:P

[leon]

Yea Alex I will have one of those please.

Leon

[glend]

Seems a waste of the aperture to put it in the USA, it belongs in the Southern Hemisphere. It wouild make a nice partner to the "Black Widow".

[FlashDrive]

At my place .... !! :thumbsup:

[glend]

Alex, this one looks like something you might build, and it is bigger.


https://youtu.be/m3l3wY1wemM

[Outcast]

LOL... don't encourage him... :lol:

[glend]

Why not? Alex, here is an idea that i have had for many years, build a large primary mirror out of ordinary hexagonal mirror tiles. Hexagonal shapes suit curved surfaces. You only need to construct a parabolic subframe, which could be laid up with thin strips of plywood laided up diagonally with epoxy adhesive. Another option would be to shape the parabola surface out of surfboard foam glued to a plywood subframe. There are plenty of sources for hexagonal mirror tiles, like this one:


https://www.amazon.com.au/Hexagonal-Mirror-Mosaic-Tile-100/dp/B07DF5W7L6

Mosaic sheets are easy to layup, and individual tiles are easy to replace.
The James Webb Space Telescope uses mirror tiles. Sure these Amazon ones are not likely to be 1/12 wave surfaces, but does it really matter when you have such a large composite mirror surface reflecting onto a secondary location.
Imaging a 2 metre diametre primary made this way. :question:

[Outcast]

Coz, he'll do himself an injury trying to setup something that colossal..:)

[xelasnave]

You all probably won't believe this but over the years I have had a few ideas to build various telescopes..I have only built two in my time..one using a shaving mirror in a balsa frame with a microscope eye piece... the seven images in that one were quite sharp ... I did build a decent 10 inch with a fork mount ... It worked great.
But I have give thought to making a blank using pottery clay to approximate shape and firing it with plate glass such that you would have a glass surface atop of the fired clay ..I think that would work..I had plans to gather crystal from the rain forest down the road from the old place and make my own glass. But I must say once I saw what time exposures would show up I lost interest in big scopes.
One thing I notice with the various big scopes once completed you don't hear about them any more..I suspect they all would have problems that when encountered the proud owner perhaps loses interest.
Alex

[glend]

Yes, I have been there. It is like the challenge of building a big boat in your backyard, eventually you have to decide what to do with it. It can take over your life. In my case I got to use my big boat for some years, but I know of another where a wrecker had to be called in to remove the incomplete project.

[Sunfish]

Hexagons do not tessellate into a spherical surface. You would need to add pentagons. In addition you would need to find some first surface hexagonal and pentagonal mirrors or make your own with silver coating and they would still need to be ground or slumped I think to get anywhere close. Perhaps it would work with gaps in the mirrors to parabolise or add a corrector.

[glend]

Yes Ray, you are of course correct. I was thinking that there would be gaps between the tiles to allow the flat tiles to parabolise on the curvature of the substrate form. Typically mesh backed mosaic tiles have a separation to allow for grouting, said separation could allow for the necessary curvature. I am not suggesting it would be a high quality instrument, but it could work reasonably well for amateur use if you accept the limitations of production mirror tiles.

[Sunfish]

Perhaps metal tiles would work and be easily polished and cut to the sizes required. Not cast Beryllium like the space telescope but some other available metal , nickel plated say, which can take a polish. Nickel plating I understand from DIY telescope books is an easy backyard project.

https://www.etsy.com/au/listing/696713274/mirror-metal-hexagonal-mosaic-and

Stainless steel on ceramic?

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10566/105660P/Directly-polished-lightweight-aluminum-mirror/10.1117/12.2308200.full?SSO=1

[xelasnave]

Maybe an aluminium blank easy to shape and polish with liquid nitrogen filled coolant pipes through it so temp can be kept constant so no in and out of focus. Probably running it at neaf or below freezing would eliminate the problem of focus...computer controlled of course...And none of this standing on a ladder to get to the EP...your seat should be part of the scope with a decent harness so you can't fall out no matter where the scope points...build a decent rig.. may be run coolant thru the he frame so it does not flex due to temp change.
The challenge is the mount which must be an equatorial and I am thinking truck differentials here...one for RA and for Dec .they won't have any weight problems I expect and the load capacity of the mount should come in at between ten and twenty tons...just use decent bearings and it should be even suitable for astrophotography....now the observatory...a second hand grain will maybe.

Alex

[Startrek]

I wouldn’t think you’d get too many nights to use this monster as atmospheric conditions may limit its power ??
Unless it’s located on a mountain in the Andes ?
What’s the focal length of this behemoth ?

I’m happy with my 12” Goto dob at least I can use it most clear nights and just wheel it out of the garage with my Bunnings parcel trolley and pluck it down

When I started this hobby 4 years ago I thought a 12”” was a monster but this is ridiculous !!!

[Sunfish]

If it were a spherical reflector with a movable secondary corrector the mirror could stay fixed and be of unlimited size.