Guide Scope Mounting

[obayflight]

I am wondering if it is necessary to use rings and dovetail to mount a guide scope. Couldn't a person devise a way to mount a small pan head onto the guide scope then onto the main imaging scope? Is there a limit to the angle between the guide scope direction (where it is pointing) and the main scope's direction ( what is being imaged). I find mounting rings ungainly and clumsy to fine tune. Any help / opinions would be greatly appreciated.

[PeterCPC]

My guidescope is mounted using the Synta dovetail (9x50). As long as it points roughly where you are looking it's ok.

Peter

[LightBucket]

You could just used fixed rings if they do them for the size of your guidescope, it only has to be fairly close to pointing in the same position as the imaging scope, if  you are too far away though you will get field rotation in your images..

[Jessun]

I for one don't think that you can introduce field rotation by pointing the guide scope in a different direction. Only polar misalignment can cause this.

But it's useful for sure to aim at the same general direction to permit the scope to track at the correct speed. Atmospheric diffraction plays tricks as you go close to the horizon.

I agree that the complexity of various mounting systems add nothing really to the final result - often quite the opposite. Might as well just superglue the thing on :-D

/Jesper

[obayflight]

Thank You All So Much!

[newbie alert]

19 hours ago, LightBucket said:

same position as the imaging scope, if  you are too far away though you will get field rotation in your images..

Edited 19 hours ago by LightBucket

That's polar alignment error...

[LightBucket]

3 hours ago, newbie alert said:

That's polar alignment error...

Polar alignment error will give star drift over time, if you are guiding too far away from your target you can get field rotation..

[newbie alert]

I don't get either because I get my PA as best as I can on the given night and don't guide on a star in a separate part of the sky..it can be done thou..

[lux eterna]

On 2018-01-31 at 12:30, obayflight said:

I am wondering if it is necessary to use rings and dovetail to mount a guide scope. Couldn't a person devise a way to mount a small pan head onto the guide scope then onto the main imaging scope? Is there a limit to the angle between the guide scope direction (where it is pointing) and the main scope's direction ( what is being imaged). I find mounting rings ungainly and clumsy to fine tune. Any help / opinions would be greatly appreciated.

With my setup, using a standalone NexGuider, I sometimes have to nudge the guidescope from it´s ideal position just to find a guidestar. But with a good guidecamera that may not be necessary. I ended up with a DIY solution which also works as a carrying handle for my scope.

The bigger the polar alignment error is, the closer to ideal position you need to point without field rotation issues. Since I started being careful when I choose the best guidestar, I always get away with just an old fashioned polar scope alignment which just takes 2 minutes to complete.

[Jessun]

On 01/02/2018 at 11:22, LightBucket said:

Polar alignment error will give star drift over time, if you are guiding too far away from your target you can get field rotation..

Your typical gem can rotate in ra and dec. Assuming pa is spot on, what part of the metal structure on the mount warps itself along this third axis? 

/Jesper

[LightBucket]

29 minutes ago, Jessun said:

Your typical gem can rotate in ra and dec. Assuming pa is spot on, what part of the metal structure on the mount warps itself along this third axis? 

/Jesper

Ok,  calm down I stand corrected...

[Jessun]

Hehe, calm as a cucumber. 

The two biggest myths I've come across regarding astrophotography concerns f-ratio and field rotation.

Guiding is tricky enough as it is, with finding a guide star, getting software to work, avoiding oag prism artefacts etc etc, that it's only right to point out the single thing budding photographers don't need to worry about. 

/Jesper