Help with weird reflector telescope collimation

[joseag285]

Hi,

 

Last year I bought a Celestron 127 EQ Telescope. I have enjoyed using it and I have learned pretty well to collimate it quickly and never had any problems with it. However, a few weeks back my cat somehow managed to drop the whole thing and it hit against the floor pretty hard (seeing it on the floor hurt me so much lol). Luckily, nothing was broken. Both the primary and secondary mirrors are fine, but they obviously moved around when it dropped. However, after collimating it back and doing a star test, I noticed a weird spot on one of the "quadrants" of the light. I've attached a picture of this below. No matter how perfectly I seem to collimate it, I always get this spot on the same quadrant, even when I purposefully uncollimate it. This makes it impossible to focus the star or planet since there will be a huge coma on it. I have tried removing and putting back in the primary mirror evenly but it doesn't seem to work anyway. As I mentioned before, I am well used to collimating my telescope, but this weird spot is a first for me. The only thing that comes to mind is something to do with the focuser tube being crooked after the fall. I would appreciate any help or suggestions from people who have seen this kind of spot during observation.

[Peter Drew]

The 127EQ is one of the Bird-Jones design, it has a correcting lens fitted to the focuser tube.  It is likely that this lens has been skewed due to the fall and this would probably affect the image regardless of how good the collimation has been done.  Welcome to SGL.     🙂

[Bruce Leeroy]

Could be the focuser draw tube protuding into the light path, try racking it all the way out and taking a picture to see if it diminishes.

[Bivanus]

Hello J and welcome. I've looked for a schematic of the scope but couldn't find one, only a general drawing in an article on Cloudy Nights. Please don't be upset at the rather acid tone of that article, everybody has to start somewhere and even if other optical solutions are better the best telescope is still the one you actually use.

It seems that your scope has a Barlow inside to act as a corector lens. Interesting info in said article is that, at least according to the author, this lens has to come out for a proper collimation. This raises the question if it can be pulled out and if you did it.  If not, it may be worth a try and, like @Peter Drew says you may also look at it to see if it's centered or it moved. Also, the tube might has shifted in more than it should, thou I have a feeling that would also alter the feel of the focuser and you might've noticed it.

Not a reflector guy myself, leaning hard towards refractors, and collimation looms large among my reasons 😅   

EDIT: link to article Celestron PowerSeeker 127EQ - User Reviews - Articles - Articles - Cloudy Nights

Also, here's another article that details the corector issue Celestron 127EQ PowerSeeker Review - Not Recommended - Telescopic Watch 

Edited August 16 by Bivanus

[joseag285]

@Peter Drew Thank you for your answer. I was just thinking last night if it had something to do with the focuser tube as well. I'll see if I can take it out tonight and look into it.

 

@Bruce Leeroy You might be on to something. The picture I took and posted here has the focuser tube mostly racked all the way in. However, when I take it out past the focus point, I've noticed that the shadow is not visible anymore. This would explain why the shadow appears on the same quadrant always. Also, I believe that quadrant is exactly the one where the focuser tube protudes inside of the telescope tube.

 

@Bivanus I still haven't messed around with the focuser tube, but based on the other responses, it's very likely that that's causing the problem. As for the articles, I'm quite aware that some people hate this telescope. However, I think it's a great beginner's telescope as long as you respect its limitations and also buy some good quality eyepieces and accesories. I've taken some really great pictures and seen different deep sky objects with it, so I'm honestly pretty happy with it (except right now with this problem I have 🤣)

[Peter Drew]

It's funny how the date affects telescopes.  In 2024 a Bird-Jones telescope is often derided but if you could time travel that telescope back to the Galileo era it would be hailed as the World's finest telescope.   🙂

[joseag285]

Update: Last night I took out the focus draw tube and checked the corrector lens, but it looks perfectly fine and smooth to me. I tried collimating it without the corrector lens but it was nightime so I didn't get it quite right. The shadow spot still appears though 😕. The focuser tube seems to be in perfect condition as well, nothing out of the ordinary. Honestly I think this might be something to do with my secondary being weirdly tilted. I'll keep on trying to collimate during daytime, but for now I'm pretty bummed that nothing seems to work.

[RobertI]

Is it possible that the corrector lens has moved inside the draw tube such that you now have to rack the draw tube in a long way to reach focus? Can the lens be moved inside the draw tube at all? 

Edited August 17 by RobertI

[RobertI]

On 16/08/2024 at 04:04, joseag285 said:

However, a few weeks back my cat somehow managed to drop the whole thing and it hit against the floor pretty hard

I imagine that’s the last time you let your cat use the telescope?

[joseag285]

3 minutes ago, RobertI said:

Is it possible that the corrector lens has moved inside the draw tube such that you now have to rack the draw tube in a long way to reach focus? Can the lens be moved inside the drawing at all? 

No, the corrector lens is held tightly in place by a plastic ring that screws on top of the lens. I took it out yesterday to see if the lens had moved but there's really no way for that to happen.

 

2 minutes ago, RobertI said:

I imagine that’s the last time you let your cat use the telescope?

No more deep sky observing for her 😆😡

[joseag285]

Final update (probably): I took out the primary mirror again and realized I hadn't bothered to check the back part of it and I found this. I thought being cracked behind the reflecting surface wouldn't be an issue, but now I'm pretty certain this is what's causing the shadow on the light. The cracked area shape even looks similar to the shadow's shape. I rotated the mirror to see if the shadow will appear on a different quadrant, but I still haven't had clear skies to test it.

Honestly I'm thinking I should make the upgrade already and get an 8" Dob instead of trying to replace the inferior spherical primary mirror for this telescope. However since I live outside of the US, shipping costs and VAT will increase the cost of the telescope by about 70%  🥴

[Mandy D]

@joseag285 that is going to have a non-trivial effect on the stresses that were baked into the mirror when it was ground. i.e. the figure of the mirror will have changed.