Guidescope

[Stryda]

Hey guys, Ive currently got a SCT 8" LX10, however the guding is not going great. Im thinking of getting a guidescope to help with this, mounted piggyback. I've been looking at the etx models and from what i can tell, they'd make a pretty good guidescope, however ive read on this forum from a few people that etx's make poor guide scopes (somthing to do with the mirror lock?) just wondering if anybody can clear this up for me? or any suggestions to a better guide scope in the same price range? Thx in advance

[steppenwolf]

To avoid 'differential flexure' - where the guiding system and imaging system don't move absolutely as one - a secure and stable guide 'scope is required. Any telescope that has a mirror in it is at a greater risk of movement in the optical train so an ETX of the Maksutov type is less suitable that a refractor.

A cheap refractor is normally makes for a very suitable guide 'scope.

[Merlin66]

Tried the ETX90 as a guide scope.... looked sexy sitting on top of the SCT but it wasn't robust...and the focal length was just toooo long.

I changed over to a ST80. It is lightweight good focal length and now does the job very well.

(I also make use of an off axis guider....) your choice....

Ken

[JCJC]

I use an ST80 as well, I can usually find a guidestar with an unmodified webcam using some homemade guidescope rings.

Jordan.

[Stryda]

thanks for the input...still slightly confused....if my etx is mounted onto my lx10 surely they would both move at the same speed? albeit maybe slightly slower than without an etx on...but still at the same speed....

[Merlin66]

With or without the guide scope the drive will track the stars at the same rate. If you balance the mounting correctly there should be minimal problems.

The idea behind guiding is to compensate for any errors in your drive and/ or movement of your image in the camera. This is normally done by a combination of a "guide scope" with a "guide camera" which locks onto a star image and uses software ( PHD etc) to send signals to the mounting which either slightly move the axises of the telescope or speed up or slow down the tracking speed.

What can happen however is that the optics and the guide camera can move relative to the main telescope optics either by loose components, bending or movement in the support rings/ baseplate etc. When this happens the guide signals from the guide camera no longer match the reality of the star's movement and errors creep in.

The guide camera via the guide signals it sends to the mounting can cause over or under corrections causing the star image to appear as a line rather than as a point.

The more solid the connection between the two telescopes generally the better the guiding.

Hope this helps.

Ken

[Stryda]

Right Ken thats helped a lot . I'm pretty sure i understand now, onto scope searching

Thanks

[NickH]

ETX90 not really ideal for guiding due to focal length, but as others have said, an ST80 (£85 from FLO) will do the trick nicely!

[NickH]

And make sure you don't get those cheap and nasty guide rings which some people advertise... speak to FLO/Ambermile and the rings they will supply will last a lifetime