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SCT Focuser upgrade

Marky1973

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Davey-T

Davey-T

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1 minute ago, Physopto said:

How much did it cost?       :p

Not much but a fiddly job to fit as I recall, never tried it myself 

Not sure now if you mean the focuser mod or the hairy thing :)

Dave

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Physopto

Physopto

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I only once had to collimate my Meade. Used a ladder about 10/15 foot away in front of the scope. Screwed a metal plate to it with a small hole in it. Lined the scope up pointing at the metal plate hole. Then viewed the scope and the rings formed in the mirror and  optics. You can get a good collimation by adjusting the knobs until every thing is concentric.

Derek

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Dave In Vermont

Dave In Vermont

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I use a JMI MotoFocus on my Meade LX90 12" ACF SCT - the JMI is an excellent unit that is rarely seen 'across-the-pond.' And I installed a GSO 10:1 Crayford dual focuser on my new 150mm Skywatcher Maksutov-Cassegrain. The GSO is a fraction the price of the Moonlite or FeatherTouch offerings. And it works about as well from what I've heard and seen. But it's only available in basic-black. But if you want that 'BLING!' - look, get the Moonlite. :D

Enjoy!

Dave

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ollypenrice

ollypenrice

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I have an old Meade. I have their motor focus for it but it still moves the mirror. Surely the big advantage of a conventional focuser added to the back is that it doesn't move the mirror? So image shift is zero. I also have a decent Telescope House gadget which is just a threaded bar and spring going into the back of the mirror where the transport screw was once placed. It pulls back on the mirror all the time. With a rear-fit focuser you can pull the main mirror back slightly with the mirror focuser to get it settled and then fine focus with the Crayford or R and P. There seem to me to be no disadvantages with this system for planetary.

Olly

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swag72

swag72

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My first experimentation into long focal length imaging was with a C9.25. I fitted the FT micro focuser to it and also a friend made me a thing that fitted around the focuser knob and scewed on and connected to that was a long lever - Focusing was really easy with that. I have to say that I didn't experience any mirror flop issues with it either....... 

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ollypenrice

ollypenrice

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Posted
19 minutes ago, swag72 said:

My first experimentation into long focal length imaging was with a C9.25. I fitted the FT micro focuser to it and also a friend made me a thing that fitted around the focuser knob and scewed on and connected to that was a long lever - Focusing was really easy with that. I have to say that I didn't experience any mirror flop issues with it either....... 

Hehheh...

microfocus%203-L.jpg

Now Tom can't get on with this gadget at all but I love it, and it holds focus with total reliability on the zenith. The smallest movement you ever make on the black knob is a 180 degree turn - and that's what you call fine focus. I made it because the slow speed focuser was missing a bit on my second hand Tak but, when the missing bit turned up, I'd come to prefer this to the standard fine focuser on the parallel scope so I've stuck with it.

Besides, it's as eccentric as I am so we get on fine.

Heath Robinson.

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Dave In Vermont

Dave In Vermont

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Posted

The trick to using a Crayford-focuser with an SCT or Mak is to first focus the knob for moving the mirror all the way foreward to lock the mirror. And leave it there. Now you can use the Crayford (or Moonlite) exclusively to focus your scope. Thus: No more mirror-flop.

For the Meade LX90, LX200, etc. series, the stock focuser is poorly designed junk! People have complained to Meade about this for decades - and Meade has responded by offering it's new LX650-series - for almost 2X the price of the LX200's! They did fix this in the 650.....Idiots. There is a solution though:

http://www.petersonengineering.com/sky/ez_focus_kit.htm

If you're going to keep using a Meade LX-series scope with the regular focuser, at least think about installing Pete Peterson's kit. It's excellent and makes a world of difference.

Dave

PS - He will be happy to ship his kits worldwide for extra postage.

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Colinlp

Colinlp

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Posted

I've just bought a Moonlite CS with the large format fitting for my CPC (in green to match the Televue eyepieces and Powermates I haven't bought yet!!).

 

I'm going to have a go at the SGL Arduino focuser for it which should be a bit cheaper that the pucker Moonlite version and more fun to build

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Marky1973

Marky1973

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Thank everyone - some great ideas to think about.

What I was just looking at was the c9.25 and whether the Skywatcher CST focuser would work with it (with any necessary adapters) or would that be selling the OTA short? I have read some good things about it, but appreciate it ir more of a budget option than some of the others. Money saved could be put towards the 0.63 reducer. Sounds like a focuser on the visual back with a home-made effort to lock the stock focuser might be a way to go, depending on weight...

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Owmuchonomy

Owmuchonomy

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Posted

Dave's suggestion is the only one I can see working in my mind. Why would you put a micro focusser on when the mirror does its own thing anyway.  Without a locked mirror or as Olly says a mirror that doesn't move it is totally useless. One day I may do my own mod but for now I can live with it. My SCT is about 9 years old and the collimation is still spot on so I have been quite lucky with that. It remains the only one of my scopes I wouldn't sell on. ?

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Stu

Stu

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Posted
On 26 March 2016 at 15:00, Owmuchonomy said:

Dave's suggestion is the only one I can see working in my mind. Why would you put a micro focusser on when the mirror does its own thing anyway.  Without a locked mirror or as Olly says a mirror that doesn't move it is totally useless. One day I may do my own mod but for now I can live with it. My SCT is about 9 years old and the collimation is still spot on so I have been quite lucky with that. It remains the only one of my scopes I wouldn't sell on. ?

I have to say I agree with this. The issue for me was not the fine focus of the SCT but the fact that the mirror shifted whenever you change direction of travel. That for me made it impossible to get critical planetary ficus, so I don't see how adding a FeatherTouch microfocuser would improve the situation? It still leaves the mirror shift issue.

My solution for my 8" EdgeHD was a Baader SteelTrack focuser on the visual back, and a SteelDrive motor focuser. This for me was a brilliant solution, I locked the mirror in a central position to get focus with all my eyepieces and left it there; no more mirror shift and accurate fine focusing. You can even still move the focuser manual with no power to the SteelDrive to get course focusing done quickly.

Dave's solution of locking the mirror by pushing to one extreme or the other seems a good one for non Edge scopes, provided it still gives you enough focus range for your eyepieces.

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Peter Drew

Peter Drew

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I would be reluctant to move the primary mirror its full extent to create a mirror lock for two reasons. First, on any of my SCT's that would push the focus point well out of the rear cell needing extensions, second, a SCT is opitically optimised at "normal" focus settings, outside of those the correction changes.

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Owmuchonomy

Owmuchonomy

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Yes, I can see how the focus could be disrupted.  However, with my TV 2x powermate and ASI 120 MM the sweet spot is with the standard focuser almost fully home. This would concur with Peter's point. I can't stretch to an Edge.

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Colinlp

Colinlp

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Posted

How much mirror flop do you guys see? During focusing with the stock mirror focuser I get some movement, enough to move Jupiter just off the CCD with a 2x barlow but when  tracking it stays dead centre  never needing re centring until I refocus

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Davey-T

Davey-T

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Posted
4 minutes ago, Colinlp said:

How much mirror flop do you guys see? During focusing with the stock mirror focuser I get some movement, enough to move Jupiter just off the CCD with a 2x barlow but when  tracking it stays dead centre  never needing re centring until I refocus

None with the mirror lock, don't know why all SCTs haven't got one, how hard can it be ?

Dave

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