Re: [APML] Guide scope advice

[howard@howardedin.com]

Emmanuele,

Save yourself the headache and avoid any moving mirror guidescope.

A 80mm Short Tube (ST), typically f5 or 400mm fl, will work file to guide your lens with a ST4. I used a ST80 w/ST4 to guide my Televue 500mm scope for several years. The big advantage to the ST80's are they are light.

As has been discussed on APML before, the ST4 will guide with sub pixel accuracy. While not as accurate or as sensitive as the STV it is a great guider. The consensus has been that a ST4 can guide accurately with 1/2 the fl of your imaging device.

For manual guiding you want a longer focal length. It is possible to use a barlow with a ST80 which should provide good guiding if the eyepiece is 10mm - 12mm fl.

In either case, the main issue is flexture. If you get a cheap guidescope it may have a sloppy focuser assembly. It is possible to tune them up (consider adding a second eyepiece thumbscrew). 

Adding a barlow may  be problematic with a ST4 attached to it; this increases the load on the focuser. It may not be a big issue if you are using an eyepiece to guide.

The 60/700 you have might work if it is solid (really wonder about that .965 focuser + adapter combination) but you will certainly run into situations where a good guide star is difficult to find with the limited aperature. I would try it first since it is the cheapest route!

I am assuming you will use a good solid mounting method for the guidescope (like Losmandy rings).

Howard.
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