Newton and high power star quality

[Hakann]

This is my very first thread at the forum and I will ask on a question that has my attention up.
High powers and Newton star quality.

If you don't like to read it all, read this lines and the last..



As not so many years as a visual observer ( 3-4 years ) I has of course not a great experience.
But I has take the time 'in my way' ( as I stepped in from exactly zero in astronomy ) to learn the sky and find Messier objects and try to learn on what scope design ( and size ) what I prefer and what I like to observe, and magnification, FoV, pupil size and so on.

In my astronomy I only go visual deep-space ( no planets no sun observing ) so a Newton is the way and the bigger - the better.
I did not go the traditional way to build a small scope first or what is common today to get a smaller China Newt or Dob.
I can’t stand the China telescope ( now is that said and it’s my way and it’s not critic’s to others who use them )
I got a 18” mirror here in Sweden but now I has stepped up to a CZ 18” ( f/4 ) but it’s still on order.
In this jouerny I did prefere observe whit others or go to SP or rent scops at darker sites.
Sweden has very limited nights in where the standard is the way I like it.
( Here I has enjoy bino observing and I has got me a good bino equipment whit good optic’s )
I know a Chinese scope in this sky we has might be all ok whit a decent EP, vs the diffraction vs price and size.

On my travel I has been on La Palma several times and to Oregon SP and Sahara desert and Bortel 1 in site in Australia and Europe alps for mention I has been serious to see great sky’s !
But even if I had some good sky it’s in my ’limited’ time and at a very small time frame ( vs a trip )
But I learned the hard way as ex 3 years in a row in La Palma under December it’s not real easy..
It can be dark but bad seeing or windy or ’calima’ or moister at other places is common. ( No new's for you guys, but I thought the stars was always up there ...'almost'.
And it can be not as dark one like or light polluted vs nearby cities or clouds.. or the Moon.
Here in Sweden it’s cold and snowy ( can’t stand that actually )

I has been in some very nice telescop’s.
Best I seen into so far is a Lomo mirror in a 25” in Germany.
But I has been in optic’s like Zambuto’s, Lockwood’s, Mel Bartels, Swayze, Kennedy’s, Galaxy etc, etc.

In La Palma last out my focus topics was Trapezium and the Horse head.
( I has been in 18” scoops here in Sweden but newer saw it, and I has been whit experience observes here )

I had a German made 20” rented Dobson in La Palma.
Sky was dark, and average over 21.7 and I was at 2.000 meters. ( of course ..medium seeing as it is ’always’ something )
I saw 6 stars in Trapezium and the horse head but I never saw the horses ’head’.
I had my Ethos EP collection there and the Nikon HW’s and Astronomiks filters.

What bothers me is I never really get great stars if it is jacked-up.
In Sweden one old observer told me we cannot get much over 200X here in a 16-18" Newton telescope. ( ex a decent sky and at 'what they say' ; 6 waves tolerance )
But the ’China users’ whit telescoops that price is less what a Ethos EP cost say 50X/” is a not problem here (?)
-If not they say the observer is lousy or to bad sky or bad mirror. ( they mean a GSO mirror is all we need vs they are on diffraction at 4 waves )
I personally has hard to believe a 12"-16" Skywatcher Dob has 4 waves.
I told them I had a hard time jack it up at ex Oz Sky ( Zambuto/DSM & Obsession telescopes ) or at 3 years in a row at La Palma sky etc.
Guys here mean you fall on the 3 examples - that's why you can't go over 50X/” !
At Oz Sky they said ( 2017 in April ) Ok now we has a limit, but on darkness we had near SQM-21.6-21.8.

What I do see if I jack it up is stars is big as coins, and I don't like that and wonder why.

But is this what one get in a Newton normally ?

Example in the 20” at La Palma I had ex Ethos 6 mm = 338X and that is 17X/” and stars was not what I like to see.
Blurred big time and I did collimate many times under nights whit my own Glatters tools and the 2-pupil AC.

In the Lomo 25” ( f4.5 ) we used Ethos 4.7 mm on ex M57 ( 600X ) and this was mediocre sky ( 1.5 hours by car from Frankfurt ) and around SQM 21.3, so bad but not that ’bad’.
I like it dark but realise if one is over SQM 21 one must accept that.
I also know I can’t demand refractor style stars all the time.
In the 25” Lomo we had 24X/” and I really enjoyed that mirror ( it was told to be a 8 wave ) but what numbers in RMS nm figure/surface was not mentioned.
Mirror was 70 mm thick and made of Sitall.
Owner told me on my question of fans - it is a zero expansions glass.
Now I know even at ZE glass, at a thickness of 70 mm on the edge, and that means a boundary layer above the surface as day was hot and night was not cold ( but of course cooler )
I guess he used fans as when I was there some hours around midnight 2 nights in
a row, the mirror did perform great.
He did not use a coma corrector but did prefer Ethos EP even of ’more’ glass ( and even if he was all into high powers ( builded the scope for that vs a small diagonal at 3.9” )

So what was the ’key’ here to the great performance ?
Was it the mirrors tolerance vs stiffness ( 9;1 ) or stiffness in scope, or the rather 'slow' focal or the small diagonal or if we had good seeing - I don’t know.
Owner told me you should use the scope in Austria alps at 2.500 meter at 1.000X on ex M57.
But towards my Sweden buddies, even if he goes 1.000X he is only at 40X/” up at the alp's whit Lomo optic’s in Sitall, and they is in low buck EP and China scopes in mediocre Sweden sky and +50X/” is a no problem (?)

I did try to explain to them how I see it and the sky I been at and in optic’s I look into and observes that has doing this for many years.
-But they say I’m not ’experianced’ yet.
( Ok so it can be if we was talking faint galaxys, but my eyes is ok so I know if a star is blurred or not )


If they can see pinpointed stars, why can’t I ?
( realise few or non invest here in good optic’s or bigger scoops as sky is so bad )

In my astronomy now I enjoy to learn to trace the object’s and ’eye candy’, but I know I will be chasing faint stuff down the road and I’m not afraid go to Chile or wildness Australia etc later on.

In scope build's I’m into cellulars design on the mirror and very stiff scope constructions.

From Aerospace I do know how hard ( if even possible at a 500 mm optic’s ) to test 10 nm RMS etc equal to ATM’s PV wf 8 wave.
I heard all kind if high numbers from ATM, but I shut for 15 nm RMS figure/surface @ 632 nm.
In ATM that is consider rather low ;-)
-No matter of glass material, thickness ratio or focal or dimensions.

I hope you might get my question.
Blurred stars in Newton's & sky quality.
Maybe one need to has blurred stars to see the faint stuff ?