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How does one frame the target with a refractor?

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6 replies to this topic

#1 betelgeuse91

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Posted 28 September 2022 - 07:11 PM

For imaging, I am wondering how framing can be done for threaded connection. 

 

I have a redcat51 and it has a rotator, so it allowed me to rotate my camera. But I notice that most telescopes don't have this kind of built-in rotator.

 

For that case, how does one rotate the system to frame the target? (for threaded system, so there is no clamp screws)

 

Thanks!



#2 qswat72

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Posted 28 September 2022 - 07:15 PM

Some refractors come with a rotator that is either built in, or can be threaded on. There are also threaded rotators that can be added to an image train if you have enough backfocus to play with.

You could also put shims in the threads so that it tightens at different rotation angles, but that can lead to other issues as well.

#3 betelgeuse91

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Posted 28 September 2022 - 07:36 PM

Oh, so the imaging train must have a rotator after all... Thanks.



#4 Jim Waters

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Posted 28 September 2022 - 07:56 PM

https://agenaastro.c...ireball rotator



#5 Rasfahan

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Posted 29 September 2022 - 05:43 AM

You can also rotate the telescope in its rings. I find that to be preferred because you are not messing with the image train alignment.



#6 betelgeuse91

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Posted 29 September 2022 - 02:38 PM

Thanks for the link. I wonder if those kind of device can introduce tilt when rotating and clamping...

 

 

You can also rotate the telescope in its rings. I find that to be preferred because you are not messing with the image train alignment.

I too thought about this, but then I am afraid that the telescope could move up and down with respect to the rings, ruining the balance



#7 Rasfahan

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Posted 29 September 2022 - 03:07 PM

Thanks for the link. I wonder if those kind of device can introduce tilt when rotating and clamping...

 

 

I too thought about this, but then I am afraid that the telescope could move up and down with respect to the rings, ruining the balance

That depends a lot on the mount, of course. I'ld feel more confident I can keep the scope well enough balanced in DEC during rotation than to not mess up my carefully un-tilted image train with a rotator.

 

I also always have something mounted that can work as a sliding weight if needed. Most entry-level mounts actually benefit from some DEC imbalance to clear the backlash (best if changed after meridian flip). Direct drive mounts need it for best performance. Friction drive mounts basically don't care within large limits. So it's only high-end (especially of going unguided with encoders) and belt-driven mounts that need a careful DEC balance.




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