Celestron C6 - Optical alignment

[dweller25]

Hello,

I am looking for some advice, here is a photo of my C6...

The "hall of mirrors" photo shows something is out of alignment - However this scope has been perfectly collimated on an in focus star at x300, with perfectly symmetrical airy rings both sides of focus !

As a double check the views of Jupiter are very close to those of my TSA102 so the C6 even with this anomaly is working quite well

I'm assuming the optics are not quite lined up right and even though I'm getting good results it would be great to know that I am getting the last bit of performance out of the scope with the best optical alignment possible.

If anyone has any clues as to what to do to affect improvement I would appreciate your feedback..... ?

[knobby]

If star test is ok , I'd honestly leave it alone !

The picture you've shown could just be your camera isn't in line with the scope perfectly I guess.

[Peter Drew]

Perfect symmetry of the "hall of mirrors" appearance is no absolute guarantee of perfect optical alignment due to centering and other minor differences. However, theoretically the reflections should be concentric. A slight tweak of the screw at the 11o'clock should produce this. If, for whatever reason, this does not improve things it's easy enough to "untweak" it.

[dweller25]

Hello Peter,

You are right, I can get all the reflections to line up perfectly by tweaking the collimation screws - but then the star test is poor and visually it does not perform as well !

Something is off center - but I don’t know what - does the photo give any clues ?

[Peter Drew]

I would suspect the secondary, but from your description of the results in the default setting I doubt whether there is any noticeable improvement to be gained.

[dweller25]

1 hour ago, knobby said:

If star test is ok , I'd honestly leave it alone !

The picture you've shown could just be your camera isn't in line with the scope perfectly I guess.

I might have to do that but would like to improve alignment if I can.

The camera image is central to the OTA - I get the same view visually

How does your C8 look from the front ?

[knobby]

44 minutes ago, dweller25 said:

I might have to do that but would like to improve alignment if I can.

The camera image is central to the OTA - I get the same view visually

How does your C8 look from the front ?

I'll take a pic tonight

[Highburymark]

This is an interesting post for me as I once had a C6 which appeared to be well collimated but I was never really happy with the views. It did suggest there is greater variability in SCT optics than those of refractors, and contributed to my current all-frac set up. Would be interested to hear how you progress. 

[AndyH]

I remember reading many many years ago regarding an Intes-Micro 6"F10, that was perfectly collimated but was out of mechanical alignment to the tube. I wonder if this is that effect ?

What has been seen, cannot be unseen. That would bug the hell out of me ?

 

Andy

[knobby]

As promised, pic below ... Not sure how far away you were but I was about 1.5 m away.

Looks very different to yours .

it was very difficult to get the camera centred too, had some very weird results when off centre a bit .

[dweller25]

Thanks knobby, I think you are too close, perhaps you could try another one at approx 2mts (your focal length) ??

I pulled back until the edge of the secondary was right next to the edge of the primary - approx 1.5mts for the C6

[AndyH]

I can't remember, but can a SCT's primary be collimated?

[fozzybear]

Just a thought has the corrector been removed for cleaning and not put back in correct orientation as I can remember these optics where matched and there used to me a mark/code etched onto the edge of the corrector and inside the scope a line etched and some cork shims these held the corrector in optical centre over the optical axis of the scope.

I do have an old manual for a C8 if of interest I can email to you

Regards

Andy

[knobby]

Blimey, 2 meters away and the slightest movement makes a massive difference

 

[AndyH]

Have you tried turning the focus knob either way, then re-checking from the front. I'm wondering if there's been some tiny bit of primary mirror flop having the scope horizontal for the pic. Just thinking out loud whilst sipping on a cup of coffee......... just ignore me if that's a silly idea 

 

Andy

[dweller25]

3 hours ago, AndyH said:

I can't remember, but can a SCT's primary be collimated?

Sadly - No

[dweller25]

3 hours ago, fozzybear said:

Just a thought has the corrector been removed for cleaning and not put back in correct orientation as I can remember these optics where matched and there used to me a mark/code etched onto the edge of the corrector and inside the scope a line etched and some cork shims these held the corrector in optical centre over the optical axis of the scope.

I do have an old manual for a C8 if of interest I can email to you

Regards

Andy

Hello Andy.

I don't think new SCT's have the orientation marks on the corrector now so I guess they are not matched.

The corrector was bought new and is as it left the factory.

Thanks for the manual offer but I think at some point I will measure to see if the secondary is central or not.

 

[dweller25]

3 hours ago, knobby said:

Blimey, 2 meters away and the slightest movement makes a massive difference

 

Aaah thats more like it - yes your scope looks to have concentric circles - as it should have.

[dweller25]

3 hours ago, AndyH said:

Have you tried turning the focus knob either way, then re-checking from the front. I'm wondering if there's been some tiny bit of primary mirror flop having the scope horizontal for the pic. Just thinking out loud whilst sipping on a cup of coffee......... just ignore me if that's a silly idea 

 

Andy

Good idea Andy  - I actually do this when collimating, but it does not help the front view problem.

The good news with this scope is that it has ZERO image shift which is nice.

[AndyH]

33 minutes ago, dweller25 said:

Sadly - No

Ballsocks   If a scope is mechanically off, yet collimated, the article (from memory) talked about aligning the primary using a laser and a target at closest focus, then collimating both mirrors as normal. So that's a dead end.

EDIT: Not that i'm saying that your optics aren't aligned to the tube. Could be something else

 

No image shift is VERY encouraging !!

[newbie alert]

If the star test shows it'd collimated and holds its collimation for a length of time then it's performing..

I try not to look for problems but sometimes they just hunt me down

[dweller25]

I have decided to leave it as is.

Performance is very close to a TSA102

Thanks for the responses