RC6 - What tweaks does my collimation need?

[Melitastro]

I've just finished cleaning and setting up my scope after moving to a new home. The collimation seems pretty close but obviously needs a final tweak and I'm not sure exactly what adjustments are needed to get it spot on

This is the focused image:

This is defocused inwards, with the lower image showing some detail of the bright star:

And finally, defocused outwards:

Does anyone have some advice on the steps to follow to complete the collimation? I don't want to adjust the wrong mirror, or adjust them in the wrong order and find I'm making things worse!

Tony

[newbie alert]

I've not got a RC but looks abit thick and a bit thin on the opposite side  on your defocused star 

[GalaxyGael]

4 hours ago, Melitastro said:

I've just finished cleaning and setting up my scope after moving to a new home. The collimation seems pretty close but obviously needs a final tweak and I'm not sure exactly what adjustments are needed to get it spot on

This is the focused image:

This is defocused inwards, with the lower image showing some detail of the bright star:

And finally, defocused outwards:

Does anyone have some advice on the steps to follow to complete the collimation? I don't want to adjust the wrong mirror, or adjust them in the wrong order and find I'm making things worse!

Tony

Do you use a tilt adapter to which your focuser is attached? 

[newbie alert]

This may help to show what proceedure is needed to adjust what part..

 

[Melitastro]

3 hours ago, GalaxyGael said:

Do you use a tilt adapter to which your focuser is attached? 

Yes, I have one in the imaging chain

[Melitastro]

2 hours ago, newbie alert said:

This may help to show what proceedure is needed to adjust what part..

 

Thanks, I've viewed this before, but it doesn't touch on analysing star images to get an idea of what is causing the collimation error

Tony

[newbie alert]

1 hour ago, Melitastro said:

Thanks, I've viewed this before, but it doesn't touch on analysing star images to get an idea of what is causing the collimation error

Tony

I use a sct and the central doughnut caused by the secondary.. sure it be the the same for a RC 

[licho52]

With the cheap RC and I now have the 8" version, at some point I consider it to be "close enough"  I found that if I don't I tend to make it worse and then spend another few hours playing with collimation screws....while mumbling foul words incoherently.

I think you've reached the "close enough point."  Trying to be a perfectionist with these scopes is self-destructive!

[Melitastro]

5 hours ago, licho52 said:

With the cheap RC and I now have the 8" version, at some point I consider it to be "close enough"  I found that if I don't I tend to make it worse and then spend another few hours playing with collimation screws....while mumbling foul words incoherently.

I think you've reached the "close enough point."  Trying to be a perfectionist with these scopes is self-destructive!

Thank you, I think those are wise words. Unless someone out there can make a rigorous analysis from those images I'm going to leave it as it is 🙂

[GalaxyGael]

Agree that you are in the close-enough territory. I asked earlier in the thread if you use the tilt adapter for the focuser, since that is one way to deal with the offset ghost in stars. your secondary might be fine and the relationship between the primary and the focuser could have a slight nudge. But that would mean checking all three again as they have a tight relationship. Not to worry if you have done that, but if you have the tilt adapter and have not done so, you might dial it in given you are able to get it this far with the collimation.

[Melitastro]

3 hours ago, GalaxyGael said:

Agree that you are in the close-enough territory. I asked earlier in the thread if you use the tilt adapter for the focuser, since that is one way to deal with the offset ghost in stars. your secondary might be fine and the relationship between the primary and the focuser could have a slight nudge. But that would mean checking all three again as they have a tight relationship. Not to worry if you have done that, but if you have the tilt adapter and have not done so, you might dial it in given you are able to get it this far with the collimation.

OK, thanks, I'll probably leave well alone seeing as you agree that it's looking pretty good. I don't want to spoil anything now I've got it this close 🙂

[licho52]

There's nothing better than a well collimated RC, makes me feel like a real astronomer.

With a way more expensive refractor I am merely a photographer....

[Clarkey]

I have an RC8 and have spent many hours going round in circles trying to get it 'perfect'. Eventually I came to the conclusion that with the cheaper GSO RC's this was as good as I was going to get. I would say you are about as close as you are likely to get by eye. The inner spot is indicative of good collimation (the name eludes me). The DSI collimation procedure is quite good for star tests, but I found a method using a combination of the TS RC collimator (secondary) and star testing (primary) worked well.

The only thing I am planning to do is get a ronchi grating to get the FL of the mirrors spot on. Some seem to quite along way from the published FL.

[Melitastro]

10 hours ago, Clarkey said:

I have an RC8 and have spent many hours going round in circles trying to get it 'perfect'. Eventually I came to the conclusion that with the cheaper GSO RC's this was as good as I was going to get. I would say you are about as close as you are likely to get by eye. The inner spot is indicative of good collimation (the name eludes me). The DSI collimation procedure is quite good for star tests, but I found a method using a combination of the TS RC collimator (secondary) and star testing (primary) worked well.

The only thing I am planning to do is get a ronchi grating to get the FL of the mirrors spot on. Some seem to quite along way from the published FL.

Thanks, I haven't seen mention of the TS RC Collimator before, so I'll give that a look and see what sort of results people have managed with it

[Clarkey]

Apparently it works OK with the RC6 so might be worth looking at. However, looking at the results you have already I'm not sure I would bother.