Monthly Archives: March 2014

Freeing my guidescope

For several years I’ve been using the same guidescope setup.  That is, a SkyWatcher ST80 mounted onto my Meade LX-90.  When it works this setup is great.  With a webcam in the Skywatcher, and a DSLR in the LX-90.  Running K3CCDTools to do the guiding.   My setup has a big and common problem, sometimes I cannot find a star to guide with!

The root cause of the problem is that the guidescope is mounted on my Mainscope using tube rails. The Guidescope is ridgedly tied to the mainscope and cannot be moved outside of a very small area.  At the weekend I was attmpting to take a photo of M51 – The Whirlpool Galaxy.  After aligning the scope and slewing M51 into the field of view, I attempted a photo – 5 min unguided.  This worked reasonable well, there was some star trailing.  It proved that the scope was on target.  I then attempted to put a star into the field of view for my webcam (Phillips TouCam Pro II) this was not successful.  There simply wasn’t a bright enough start in the field of view to register on the K3CCDTools software.  I then loosened off the scope rings as much as I could, but this had no effect, there simply wasn’t enough play to allow me to put a star – any star into the field of view!

I’m currently in the process of trying to come up with options to solve this “interesting problem”.  The tube rings that I’m currently using are the Astro Engineering AC441 Parrellel rail system with 5″ rings.

So what are my options?

1. Bigger rings?  That should give me more play, so that I can point the guidescope seperately to the main scope.

2. Install the guidescope on it’s own swivling mount?   This way, the guidescope can be seperatly pointed to the closest conveniant guidestar.

3. Get another telescope to use as a guidescope

 

So for my options, the one that is going to solve it without any doubts is option 2.  However, it comes at a price.  I’d need to completely replace the dual rail system with a Dovetail bar, onto the new dovetail bar, I’d install a Skywatcher GuideScope mount.  Then to that, I’d need to source a new set of rings with a dovetail that can be attached to the Guidescope mount.  This will give some movement, but will cost over £300 to implement.

Going for a smaller telescope is also an option.  I could get a 70mm Skywatcher Mercury.  It’s an f/10 scope so matches my LX-90 focual length.  The scope would mount into my existing tube rings.  but there does remain the question of if I can get enough play to make this work, also with the 10mm less light gathering, it may not help when it comes to finding guidestars.

So finally my option 1, get bigger rings.  Currently, I have the 5″ rings mounted on my dual rail system.  There are 7″ and 9″ rings in existance.  With that in mind, I figured that the 9″ rings are going to be too large, and won’t grip the scope.   I’ve just managed to find some 7″ rings, which comes with a complete set of bars too (which means spareparts to me)  This will give a couple of inches of play around the ST80 that I currently don’t have.  With any luck (and yes there will be an element of luck involved here) this will mean that I can mount the ST80 and adjust the position to get me access to a good 30° sweep of the sky, or larger.

If this experiment works out, I’ll be able to point the guidescope at a nearby bright star even when it’s not close to where I can currently point.  There are limits on the amount of distance that I can slew away from the main scope before strange things will start happening, but there should be a star close enough to allow the guider to work.