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focuser for sct


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i will soon be purchasing a new scope, it will either be a celestron 9.25" or 11" sct, any one recomend a focuser for it, or will it make much difference,

also would a better star diagnal be a big improvement to the standard celestron diagnal,

ive been looking at the william optics diagnals on FLO, will they be a big improvment??

any thoughts please

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i will soon be purchasing a new scope, it will either be a celestron 9.25" or 11" sct, any one recomend a focuser for it, or will it make much difference,

For what purpose?

For low power work (DSOs) the stock focuser is just about usable. It's too coarse for high power work, even visually, and mirror shift can be an issue for imaging.

The Feathertouch replacement focuser knob (with 10:1 microfocuser) is light, convenient & solves all the issues except mirror shift. Bolt on Crayford focusers eliminate that as well but they are heavy and can have slippage issues - why does no-one use rack & pinion instead of relying on metal-on-metal friction? Nevertheless probably the best solution for planetary imaging, if motorized.

also would a better star diagnal be a big improvement to the standard celestron diagnal,

The supplied diagonal actually works fairly well, within its limitations ... but IMHO a 8"+ SCT needs a 2" visual back & diagonal. As for the diagonal itself, optically there's not a lot of difference, but which is best for you depends on which eyepieces you have - the WO diagonals have a tendency to bite TV eyepieces, and vice versa, because of a difference in the dimensions and location of the "safety" cutout in the barrel (which actually makes it more likely that you will drop the eyepiece. Why oh why can't we have smooth sided barrels?)

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An aftermarket focuser is really an imaging 'must' more than a visual. I agree that a 2 iinch diagonal is also a must so as to use very wide field EPs which open out the view in SCTs. The Moonlite carries the imaging reducer in the drawtube, which is a nice way to maintain chip distance.

Brian is so right about these wretched safety grooves which have surely done in ten times as many EPs as they have saved!

Olly

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I bought a William Optics crayford focuser, a monster. It looks great and works well but the focuser on my C8 works almost as well. My best buy was a non branded WO clone dielectric diagonal, replacing the Celestron one, and it makes a good deal of difference in terms of brightness and sharpness. Both from astro buysell.

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Well the best choice is the FeatherTouch focuser as it's light and compact, the downside of course is ££££££££££ ;)

The Telescope Service Monorail focuser is excellent. Very strong, no sag and will handle a 4Kg load and not that expensive. It is however bulkier than the FT.

http://www.teleskop-express.de/shop/product_info.php/info/p3947_TS-2--MONORAIL-Dual-Speed-Focuser-for-SC-Telescopes.html

I also like the Baader Steeltrack focuser which is a bit more than the TS Monorail but better finished and with a nicer focusing action.

http://www.harrisontelescopes.co.uk/acatalog/Baader_Steeltrack_SCT_Crayford_Focuser.html

And yes I also recommend changing to a 2" diagonal so you will be able to use wide angle 2" eyepieces. If you're not going to add a focuser then you can get a 2" visual back and use a regular refractor type push fit diagonal rather than an SCT diagonal.

John

My old CPC 1100 with FeatherTouch focuser. Replaced by a 14" OO dob with StellarCAT.

Edited by johninderby
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