25" whit a 3.1" diagonal

[Hakann]

My progress whit the SDM 18” whit a CZ primary Quartz and a Antares 4” Quartz secondary is going just fine.
Carbon fibre trusses is ongoing etc, and the design has take some time but we are at the end of that now.
Peter Read at SDM is a great guy to work whit!
Positive and endless way of ball around the idea a customer wants.
CZ is soon done whit the optic's.


But over to more future telescope ideas!

My progress of what I want in future has change, but I had been into ZTE free glass since I got involved in this and I like cellular designs.
Of course, cast Pyrex is a good alternative. It quickly breathes the heat and is quite light ( ca ; 15 kg for a very stiff 25 inch at ratio 6;1 )
I have realized different telescopes the rules is different, it's economy, stationed or real portable etc, etc.
I think none of this is possible to combine today actually.
In general, however, the sky itself talks in the end, but if ..

I was very impressed by the depths of the optic’s and star quality in Jorge Peters 25” LOMO made mirrors at f/4.5 and a solid 70 mm thick.
Then the chassis was in completely ball-bearing and it was so smooth as steering it with a finger, really amazing.

-Then how good can a bigger mirror be and how much does it work to use it, plus the height.
All good questions.

I have realized a few things now.
I really wonder how good fast thin Pyrex mirror are in reality, and few show Ronchi or a star-test.
-Do they work well on galaxies etc, yes sure, but with such a large diagonal and thin mirrors added.
I’m sceptical. ( this is my personal believes )
Then the heat must come from them and before that, the figure will not be hold.
Here is an advantage of Zerodur or ULE ( or Quartz )
But even they will get warm air above the surface.
But it can be solved with fans and figure will stay no matter of temperature.

Jorge solved his idea with a small diagonal at 3.9" ( he had 16% )
So with short L-measure and without coma corrector ( f/4.5 ) and he just used it at at medium to high-power and used the Ethos eyepiece under 13 mm.
His mirror was at 70 mm, so ratio 9;1.

I could pocket a mill in ULE so ribs and the surface will be 1 "and then the heat will go out faster and the mirror becomes easier to get to work and handle.
Thin ribs are extremely expensive to get done in machining, so thicker becomes significantly easier, so less pricy.
This could AGI do in Rochester.
Ex than 85 mm thick ( ratio of 7.5 ) it would weigh just over 40 kg, vs 2/3 of a solid core.
( Ok it's double to a cast cellular ) but then in ZTE = 0 instead of 2.5.

I hope CZ could grind it at 25" in ULE on ex f/4.25 ( 2.700 mm FL or 106” )

I has never like the long set-up using a paracorr II or the SIPS, and I know more glass today don’t get a big lost, and they give one coma free image.
Anyway it all looks strange, and it can be a very long unit and with a barlow on the outside of the UTA can be around 12”..
I checked run-out of this before and its really terrible!
All loose ID and OD holes and this Crawford focusers on top of that.
Nice with a special build 'sag-free' focuser and just a eyepiece.

For example, I checked out diagonal size and has the eyepiece barrel in the primary light path, but then an extremely short L-measure i received.
With Ethos on 17 mm ocular ( 158X ) and a ok mag-drop not over 0.25, so one see that a 3.1" diagonal will work.
I tested it at a 3" vs the lip on the holder ( in reality a 3.1” )
Normally use EP will be Ethos 13 mm ( 207X )

This gives a telescope with ladder of 1 meter to zenith, but at only 12%!

If I use a L-distance at 14.37” and half FS clearance of Ethos 13 a 3.4” diagonal ( 3.5” ) that give a mag-drop at 0.2 and give 14%.
Might be a better deal as the eyepiece barrel will no be in the light path.


-Ok, there will be a little bit of coma on the outer edge ( so was Jorge’s scope as well, but it did not borrowed me )

With a welded chassis in round tube chrome molly steel ( super rigid ) and ball bearing and trusses and the UTA in CF and so light diagonal and stiff primary this would be a real 'killer'!
La Palma use of course ( vs the terrible Sweden weather & sky )

Ok 1 meter ladder is needed, but everything is always a compromise.
But okay, one is also rather relaxed on a ladder.

I know what a core of machined Zerodur ( round and ruff curve ) cost from Germany.
ULE is more expensive than Zerodur, but even a better glass for optic’s, but ok a overkill' for visual use maybe.
Quartz is at 0.5 ppm/C and chip less than Zetodur/ULE but its very hard to machine ( but price is way less )

Whatever ULE etc, what do you guys think of such a project?

-Does f/4.25 without coma corrector work ‘decent’ on medium or high-power?

I still remember 2 nights at IVT 2017 in Jorge's telescope when I went around in Veil, Crescent Nebula, M27 and M57 - that was big WOW!
Jorge said, you should use this scops in the alp’s or at LaPalma!