Aligning guide scope with OTA - important?

[RugbyRene (Rene)]

Hi all,

Quick question. I have a SW Esprit 100ED with a guide scope on top. I'm just wondering how important it is to have the OTA and guide scope perfectly aligned to aid in guiding. I usually guide at 0.7-0.8 but feel I can get better.

Cheers

Rene

[ronson]

I don't believe it needs to be perfect. But should be in the same sky area. Tracking errors are different between the celestial pole and the celestial equator.

The question is - would you benefit of anything better than 0.7-0.8? Are you planning on shooting long FLs and cameras with tiny pixels, and in location where the seeing would make sense to go more precise. If so, give it a try and let us know how you go

[glend (Glen)]

It doesn't have to be perfect, as long as thry are pointed in the same direction. After all sky rotation is a constant for both scopex. If your guiding on a star and that guides the mount, you will be right. It used to be that people would "pick" a guide star off their imaging scope light path with a prism inserted into the light path. This assumes flex in external guide scope mounting etc. The majority of imagers don't worry go much about it these days.

[The_bluester (Paul)]

I would agree with Glen and Ronson, guidescope alignment to the imaging scope is not critical. Bolt it on so that the two are lined up by eye and it should be close enough. If you had a big polar alignment error it might accentuate the field rotation if the guider is pointed a fair way off the main scope but even then the fix is to sort out the polar alignment, not the guidescope pointing.

[RugbyRene (Rene)]

Thanks everyone. It’s good to know it doesn’t need to be perfectly aligned. I can see the target in the fov of the guider so I know I’m in the same sky area.

[Startrek (Martin)]

I use my capture software APT on live view and centre a Star ( say magnitude 2.0 to 2.5 , not too bright ) in the crosshair of my screen , so OTA is centred and tracking on this Star. Then open PHD2 , use the Star profile tool screen to both centre the same Star or guide star ( roughly) and focus it at the same time watching the FWHM and HFD numbers on the dashboard.Once centred and focused , both OTA and Guide scope are aligned close enough.
I do this for both my 8” and 10” newts which have a 60mm guide scopes riding piggyback on the central axis of the Newts using solid dovetail bars and bolts.

I’ve used this method for years and it works fine

Cheers
Martin

PS: I still use my 50mm finderscope in the offset shoe bracket sometimes if needed for 1st Star alignment, but remove it after that for the rest of the night.