30” scope

[Hakann]

After OSP I came home with some new ideas that replaced my old 25” thoughts at either fast or slow focal ( I has not solved that..yet vs my ideas )
Ok, one see allot in a 14” scope or a 18” or 20”, but a big step up is 25”.
But really at 28” it start to become really nice.
I notice that before, so it’s not new for me.
At OSP, as the sky was good, faint fuzzies came up more on the agenda.
After see a faint galaxy 3 BLY away, one might get hook..

Diameter is always a matter, as the focal - so one need set up the idea from what one can do and willing to sacrifice..

So say at 30” it is a very nice deep sky or faint fuzzies scope.
Very big, but far from a 40”-50”.
At 0.8 meter, so bolted off it can go in a bigger car or a truck.

Focal at 5 is always more easy for serious power, but say at f/4, so even at a way faster scope one still need a ladder at 30”.
FL is 3 meter or 120”.
Ok tall, but not that tall.
At Zenith one need step up 1 meter, so a serious ladder is needed here.

As I’m not into low power here and was not for the 25” idea either, I think f/4 is a decent idea, and one do not need a coma corrector ( not me anyhow and especially not for mid or high powers ) as it become more easy to use a smaller diagonal ( less weight, less obstruction )
With low power I can still use my Nikon HW 17/14 mm ( 102 degrees ) EP.
I still also can use my Ethos 10/8/6 mm EP if I like the wider field.

But idea here is the TV Delites EP as light and less glass but still at 62 degrees.
This EP barrel is 1” long and they all has the focus pt 0.25” below shoulder.

Say barrel edge is half FS distance from mirrors edge, then I need a 3.9” diagonal ( 4” ) and that show me a near zero mag-drop and only 13 % obstruction.
Power at ex Delite 7 mm would be 435X.
They is aviable down to 3 mm ( + 1.000X )

I has a Quartz Antares 4” diagonal and I know in Sweden there is a 30” Pyrex core at 2” thick ( 15;1 factor )

At OSP it was shown a solution whit a dust free fan system that get air equal over the mirror.
3 turbo fans under mirror.
A very neat design.

Chassie I would do as my old former idea in welded bigger steel tube in thin wall ( bolted vs be portable in 3 sections )
Fork type design.

Drive system would be Dan Grays Sitech magnetic drive as it removes bearings etc and serious tolerances,but the negative is it need allot of power.

I found a way that Dan did like to integrate the system in telescope construction to save weight.

Ok, a scope like this need the sky and Sweden don’t has that.
But for LaPalma.

How is this idea sounds ?

[Jimi Lowrey]

If you want to hunt faint fuzzies I think you are on the right track.

[Hakann]

I really regrett myself to not bought Jorge Peters Lomo made 25" at Sitall at f/4.5.
26.000 euros was a good price for that scope.
The best scope I ever had my eye into.
That deep contrast was really something.
Ethos 4.7 mm was 600X and a big wow.

-But this 30" might be a way to go and I will meet the guy who has the core next week.

[Hakann]

A technical question for the above idea.

If I like to use a 3.5” diagonal.
Just a thought/question on that.

I can get a Pyrex 30" core here in Sweden maybe, but is just 38 mm thick, so a 20;1 factor.
Very thin for a 30" plano ( sigatta is near 12 mm vs a f/4 )

Well, thicker more weight/more glass but...and at ex f/3.5 the FL is shorter but then a bigger diagonal is needed.
( still a ladder )
But the chance of a better parabola is better at f/4, or say, more 'easy' anyway ( I add maybe as this is not easy )

I has a Antares 1/30w at 3.5" diagonal.
On the set-up for a Ethos 4.7 or the 3.7 mm, and that small diagonal the focus pt will be 1.33" inside mirrors edge.
At a 13.62" L-distance I has it ok ( from Bartels program ) for a 3.5" diagonal ( set at 3.4" app )
That is 11 % obstruction.
-I guess if that is 11 % or 25 %, might not make a big difference but 11% is nice.

But a 4" diagonal I has the EP outside mirrors edge at half the EP's field stop, but that is a total of 81 cm2, and a 3.5" diagonal get 62 cm2, so the 4" is around 20 cm2 bigger.
But the EP will intrude in mirror, and that is around 12 cm2, so it creates less space total than a 4" diagonal.

Would this ‘intrude’ cause spikes at mid or high powers ?
It is 0.17 in FoV for the Ethos 4.7 mm and 0.14 FoV for the 3.7 mm, so object's is faint stuff and a good sky is needed.

I has test put in a credit card at the side under observing at both low and high power before, and I never notice spikes from it or see a ‘worse’ image.

Ideas on this ?

A note, as to get the EP to work I will use the EP as a 'drawtube' and a own focuser body/Crawford.