SDM does a 25" folded Newtonian.

[gb_astro]

Just noticed the SDM site has some details and photos of a makeover
of one of Peter Read's older scopes to a convertible Newtonian/Folded Newtonian.
Looking through a 25 incher while standing on the ground must be nice!


http://www.sdmtelescopes.com.au/


gb.

[pgc hunter]

Definately my plan of attack when I get a big scope! Ladders suck can't imagine hunting limit of vision objects 10 feet off the ground standing in an awkward position on a tuny rung

[erick]

My next step in the distant future has to be to a 24" reflector, but I have to be able to stand on the ground. I'll watch, with interest, the ongoing developments in short focal length scopes.

[noswonky]

The SDM scope isn't a particularly short focal length - it's f/5, but with a folded light path - three mirrors with the eyepiece half way up the tube instead of at the top.

However, the SDM site says on the prices page:

"The Compact scope is no longer made or offered. All scopes are classic style only."

[GrahamL]

I must be missing something , how is the focuser / central obstruction not appear offset?

[erick]

Thanks Peter. Yes I recognise that this particular scope is a folded design. The Compact scope that SDM no longer makes is of the style of SDM#024.

I'm interested in the short focal length mirrors. SDM has already used a few shorter fl mirrors - eg. SDM#s 18, 22, 36. Check SDM#036 - 22", yet feet on the ground (almost, "tippy-toe"!)).

Check the Starmaster scopes using Mike Lockwood's mirrors down to f3.3. http://www.starmastertelescopes.com/

Mike has also demonstrated a 20" f3 scope. http://www.starmastertelescopes.com/MX20.htm

....and a 14.5" f2.55! http://www.loptics.com/fast14p5.html

[Satchmo]

There are already some very successful short focus large Newts around with Australian made optics too, including a current project of a 24" F3.5 mirror for a Canberra syndicate.

Fast mirrors, apart from higher production tolerances place greater demands on the rigidity of structures like diagonal spider and cage. The coma corrector can only work properly if the optical axis can be held very precisely to the optical axis of the Paracor.

[erick]

Glad to hear this, Mark - hopefully I'll see a few of them one day.

..........and I would reckon that precise collimation would be a very touchy task!