SCT Newbie (very) - questions

[erick (Eric)]

Unexpectedly, I have become the owner of a lovely veteran C8

http://www.iceinspace.com.au/forum/s...ad.php?t=33982

I was primarily after the Argo Navis for my 12" reflector, but have fallen for the C8, though I've only had a few brief looks through it and have yet to complete collimation. It's going to be nice little compact grab-n-go scope for me. (If you call that non collapsing tripod "portable" - one review says it is like wrestling an octopus, to get it folded up and into the car!) I've bought the right size DewNot heater to try and keep the dew off the corrector plate. I've disassembled the base, cleaned and re-greased, fitted a modern socket for the 240V power to the RA motors. I've bought a wedge and put it all together and - looked up at the clouds

BUT, out my window today , so tonight is the night to try again.

OK, first questions:-

1. Collimate with the diagonal in place? Yes?

2. With the basic fork mount, I could fix the diagonal (it's a GSO 2" quartz) in a set location for observation. However, up on the wedge I will have to rotate the diagonal to get it into the right viewing position. Hints? Can I do this effectively without buying anything else? All I have done at the moment is smear a fine layer of grease () on the flat mounting surface of the diagonal and tightened it by hand. I seem to be able to rotate it, but I have to watch that the locking collar remains tight. What is the chance it will just flip around unexpectedly and dump my eyepiece on the ground? Tricks to stop this happening?

3. Testing the diagonal mechanical performance. I reckon I centre a star, then rotate the diagonal on the scope and see how close the star stays to the centre? As well, I reckon I also try to monitor collimation by star testing at different rotation positions? Yes?

4. I picked up a 2" helical focusser:-

http://www.iceinspace.com.au/forum/s...ad.php?t=35183

I intend to find a way to fit it to the diagonal in place of the 2" eyepiece holder currently fitted into it. I will remove the current holder, hold the helical in approximate place with a few different eyepieces and see if I can pull focus. Anything wrong with my theory? And if that works, anything wrong with the practice - eg. will turning a helical focusser on the diagonal just stuff everything up? Eg. mechanically? Yes, I need an adapter to fit the helical to the diagonal and I have someone ready to quote turning up one for me. I gotta do it cheaply. Aluminium and I just flock the inside of the adapter tube?

That's more than enough questions to get started!

ps. thanks to all the great folks on IIS who have sold me this equipment for very fair prices.

[GrampianStars (Rob)]

Cool
I've an old'e 8" Meade LX5 (pre goto) with Agro Navis I use in the Melbourne suburbs. works a treat they're still good down to mag 13 so there's plenty to see
Collimate with the diagonal in. I keep mine fixed in the 1 position all the time even on the wedge. I picked up a JMI dec motor and a JMI electric focus motor as well
The 8" is great little b/yarder

[casstony]

Hi Eric, personally I wouldn't put any grease on the diagonal - just loosen the locking ring when you want to change the orientation of the diagonal. The diagonal can slip from the locking ring being loose or from the nosepiece unscrewing from the diagonal body - check that it's tightly screwed into the body, but don't overdo it since the threads in the diagonal are a bit sloppy and you might damage them.

Collimate with the diagonal in place then remove it to see if there is any difference without the diagonal; there probably won't be. You can check for astigmatism introduced by the diagonal by checking for oval shaped diffraction patterns on either side of focus. (remembering to check for astigmatism in your eyes as well)

[Mark]

Originally Posted by erick

What is the chance it will just flip around unexpectedly and dump my eyepiece on the ground? Tricks to stop this happening?

Tricks? Yes..get rid of it and use a refractor diagonal with a compression ring visual back.

I have had the experience of the locking ring coming loose..unexpectedly..allowing the 'flip & chuck' to happen, along with the sickening sound of a big 2" ep hitting the deck.

I bought a TV 'Shorty' 2" Visual Back and a 2" refractor diagonal. For all the years of my SCTing it never failed as a combo. The 'SCT Style' diag with a the locking ring 'got' me within the first week of use. Caveat utilitor.


..oh, and yes, collimate with the diagonal in place.

Enjoy that C8, it looks like a ripper.

Cheers,
Mark

[acropolite (Phil)]

I intend to find a way to fit it to the diagonal in place of the 2" eyepiece holder currently fitted into it.

Eric, you can buy a diagonal that will screw on to the back in place of the eyepiece adapter, GS make a nice quartz dielectric diagonal for around $140 . If you're not happy with the focusser then the feathertouch 10:1 focusser is well worth the money.

[erick (Eric)]

I think I already have that diagonal Phil - you can see it in the photographs.

The Feathertouch looks nice but the site says:- "The SCT MicroFocuser will not fit old orange-tube C8 telescopes."


Thanks for all the ideas and hints and tricks. I'll consider them all as I move forward - when I get the time and the clear sky.