Oh Bugger, my Secondary Holder is loose in the Corrector

[PeterSEllis]

I originally posted this on Cloudy Nights, unfortunately under the wrong Category, I'm hoping the moderators will move it for me, then it occurred to me that I should post it here, we have so good local experts.

I brought a Celestron C9.25 Edge HD straight from the Astronomical Supplier, and it is about 1 year out of warranty. The other day I went to open the dust cover on the secondary collimating screws, and the whole secondary holder rotated, worst still is that the hole in the corrector is larger than the secondary holder, so it can move up and down and to the sides. My first thoughts having found this, was to mentally take the person who did the final collimation in the factory, and put them in front of a firing squad. Either due to forgetfulness or slackness, they didn’t bother to tighten up the secondary baffle after final collimation.

So now begins the saga.
My understanding of all this is:

1. Primary Mirror is centered on the primary baffle; the primary baffle may or may not be mechanically centered in the tube (luck of the Gods with that one).
2. The Corrector plate is centered on the Primary Mirror.
3. The Secondary Mirror is centered on the Primary Baffle.

Please correct me if there is something I’m overlooking, or my interpretation is incorrect.
My first stage at correcting this situation is to borrow a technique from one of Broke Astronomer’s youtube’s ( bless you heart for posting that youtube).
The results are shown in the two pictures below.

The first picture shows the secondary holder slightly off center, the second picture, with the secondary mirror in the holder, shows the secondary mirror is centered in the secondary baffle and the small hole in the middle of the secondary mirror, which I’m assuming is the Primary baffle, is centered on the secondary mirror. If I’m correct, all is good so far.
My assumption is that the Corrector is centered on the Primary Mirror (did the factory get it right). I have no idea yet how to test this assumption. If someone has a good method of checking that the Corrector is centered on the Primary Mirror, I’m all “ears”.
If my interpretation of those images is incorrect please, let me know.
If experts think that I’m on the right track, then my next step is to use my Hotech Advanced Collimator to collimate, followed my Metaguide for the final collimation.
The problem with the Hotech method of Centering the Corrector, is that it assumes the Secondary Mirror Holder is Centered in the Corrector, and that my not be the case.
“All advice is gratefully accepted”.
I would prefer not to go for my final solution unless I have to: take a bloody large sledge hammer to the C9.25Edge, and then send the resulting picture to Celestron, telling them what I think of their quality control.


Cheers
Peter

[Merlin66]

Peter,
My opinion....
""
the second picture, with the secondary mirror in the holder, shows the secondary mirror is centered in the secondary baffle and the small hole in the middle of the secondary mirror, which I’m assuming is the Primary baffle, is centered on the secondary mirror. If I’m correct, all is good so far.

""
Go with this second set-up and move forward.
Only question I have is how to "lock" the secondary holder in this position...

Using an artificial star will, I think confirm the collimation.
ken

[PeterSEllis]

Hi Ken,
Thanks for your reply. Locking the secondary mirror into position is easy, you just remove the corrector plate and screw up the secondary baffle until it is snug up against the corrector plate. I think that I'm ready to try for full collimation, but thought I would see what the experts had to say first.

Cheers
Peter

[miker]

Peter, this Cloudy Nights thread might ease your mind. It appears to be quite common.
https://www.cloudynights.com/topic/687729-c8-secondary-problem/?hl=%2Bloose#entry9880682

If you can not get it sorted, contact Bintel in Sydney. I would be surprised if they could not help.

Michael

[Nikolas]

This is how to remove the front assembly (https://www.youtube.com/watch?v=e66yIuD3cMk). easy enough to fix if you know yourself around a screwdriver and this one https://www.youtube.com/watch?v=e66yIuD3cMk

[PeterSEllis]

Thanks Michael for you reply, an interesting thread, nice to know I'm not alone. Bintel could be a fall back position, but I have spent a life time fixing things (40 years plus), it goes against the grain to give up on it.

Cheers
Peter

[PeterSEllis]

Hi Nikolas,
Thanks for your reply and the links. I know the "way of the screwdriver", I have spent a life time fixing things, and I am not frightened to take off the Corrector, or disassemble the whole telescope for that matter, if need be.

Cheers
Peter

[Nikolas]

Looking forward to see how it all goes. keep us posted ;)

[multiweb]

There is a gap between the glass and the secondary cell. That's just the way it is. It allows for contraction and expansion when the corrector changes temperature and you can also have some room to center your secondary. There should be two rubber washers back and front as well so you can't pinch the glass when you screw it tight. It's by design. No firing squad needed. All you have to make sure really is that you kept the orientation of the secondary vis a vis corrector and primary and you'll be ok.

[PeterSEllis]

Hi Marc
Thanks for your comments. The orientation of the corrector is not a problem as there are engraved marks on the corrector (3 o'clock is the orientation of my Corrector). The orientation of my secondary is problematical, as it is rotated and I'm not sure by how much. I did read on Cloudy Nights that the mark on the secondary lines up with the Corrector marking, and my secondary does have a mark on it. I'm not sure whether this is Chinese whispers or fact, but it is a starting point.

Cheers
Peter