Ritchey Chretiens and collimation

pmrid (Peter) · #1 13-09-2009, 07:47 PM

Folks, I'm in trouble and need help. Having succumbed to the necessity to flock the baffle tube in my GSO RC 8", and having read Paul's helpful note on how to do this, I went ahead. When I removed the baffle tube, the whole primary mirror retaining assmbly came with it and in consequence, so did the mirror. No damage but I have reassembled and collimation was clearly out and needing to be redone.
In the absence of any owners manual, I went looking for guidance and thought that instructions for collimating a SCT would be pretty close. Wrong!! I should not have touched the primary, as it now appears, and should have confined myself to the secondary. I didn't know that at the time.
So now, I have tinkered with the primary and have just come inside from having tried to do the same with the secondary. The long and the short is that I have totally screwed up the collimation of my RC and am well and truly at the hair-pulling stage. If I had more hair, this would be a worry.
I need help to retrieve what is obviously a bad situation and wonder whether there is somewhere where I can send this scope to be professionally recollimated.
Peter

dpastern (Dave Pastern) · #2 13-09-2009, 09:00 PM

My suggestion - PM Peter Ward and plead for help. I'm not sure what to suggest, as I have no experience with RCs and the last time I collimated was nearly 20 years ago my my el cheap 3" newtonian.

Dave

gregbradley · #3 13-09-2009, 09:40 PM

Here is the RCOS writeup.

Only problem is they use a Takahashi Collimation scope.

http://www.rcopticalsystems.com/supp...ollimation.pdf

Greg.

Doomsayer · #4 13-09-2009, 10:11 PM

Indexing of the two mirrors is also usually important. It is likely that the two mirrors are figured to be postioned in a particular angular postion relative to one another. If they are out of index, less than optimum performance is a likely consequence.

Now that you have it apart, it would be a good idea to put a small centre spot on the secondary mirror with a fine felt tip. This will aid greatly in realignment of the primary baffle if it has moved and the secondary collimation if required.

Does the primary mirror have any internal means of adjustment exposed? I gather these GSO primaries are 'fixed' at the factory.

I have found that the combination of a Catseye 2" autocollimator, 2" sight tube and a 2" laser works really well for RC collimation - I also have a tak collimator scope. You also need to be confident that the focuser is levelled and centred relative to the secondary and optical axis. (The tak scope, laser and autocollimator work best with an accurately centre spotted secodary).

It may well need to be sent back to the factory if the mirror can not be positioned easily.

guy

Paul Haese · #5 13-09-2009, 11:31 PM

You are not in an enviable position. From what I understand, yes angular alignment as well as optical alignment is critical here. A Tak scope is probably a good buy, but given the cost of them, well send it back to the factory and get them to fix it up. It might cost a bit to do it, but at least you will know it is done correctly.

How did the primary assembly come adrift? Did you undo the screws at the rear of the scope?

pmrid (Peter) · #6 14-09-2009, 12:54 AM

Sending it back to the factory seems the only sensible thig to do. How can I accomplish this?

As for the sorry history of this whole process, here it is.

When I reached this stage of disassembly with the end off and the primary exposed, the baffle tube unscrewed with difficulty and in the end, the retaining ring as shown in the picture also came with it. Leaving the mirror sitting in the base of the scope.

At that stage, I wasn’t aware I had a problem since I believed the mirror was held in place by something more than gravity. I put it away out of the air while I flocked the baffle. It was only after that had been done, when I retrieved the base to reassemble the scope that it became apparent the mirror was not firmly held. As I moved it, the mirror shifted and nearly fell. In the process, I managed to get a great thumbprint on it and that’s when life got difficult in the extreme.
The mirror had to be cleaned and since it had already materially shifted position, there was no turning back. I took the mirror out of its base and did the usual careful washing routing as with any mirror.

Now, the nightmare continued. After the mirror was cleaned, I moved to reassemble it. There were 2 plastic shims (big washers) under the mirror and a plastic insert that protected the central hole in the scope. With everything back in place, I refitted the retaining ring shown in the photo above and tensioned it up firmly but not overly so. There was still serious movement in the primary mirror despite the collar being as firmly screwed up as I could get it without risking the mirror. I rattled. It was not firmly held.

This was a disaster. I am confident there were only 2 shims and that I reinstalled them but the mirror was no longer firmly held in its cage. I made another shim out of thin plastic sheet and fitted it under the mirror with the others. This seemed to make the difference and the central collar and baffle tube tightened up onto the mirror and held it firmly in place. I fitted it believing that somehow, I had removed another shim that I had misplaced. At 62 I am not beyond forgetting things so I assumed I had had a seniors moment at a critical time and had somehow managed to lose a shim. Somehow, I don’t believe it but it is the only explanation that makes sense to me.

The scope was ready for reassembly but obviously the orientation/placement of the mirror was entirely random.

I reassembled it fully and hoped for the best. That was not to be.

I have obviously compounded my errors many times over by attempting to collimate by adjusting the primary first. But the last of my RC woes is not over. I have a FeatherTouch focuser coming from the States to replace the GSO version and it will be useless if I can’t get the scope right.
That represents a lot of money down the gurgler because I tried to fix the defects in this scope.

Peter

Gama · #7 14-09-2009, 02:34 AM

Go to Cloudynights, there was a similar issue, and it was aligned fine using simple collimation tools.
You will need to search for it though.

Theo

Paul Haese · #8 14-09-2009, 09:14 AM

That is a bit unfortunate. It seems odd that the mirror and everything should come out. It is recoverable and you should be able to recollimate the telescope.

renormalised (Carl) · #9 14-09-2009, 12:21 PM

What this says to me is that the workmanship of the GSO RC's has a lot left to be desired. They may look alright and work OK, but put together using shims and such, and not having the mirror anchored to the mirror cell properly is just inexcusable. It might be done to save on costs and to make the scopes cheap(ish), but if that's the quality of workmanship you're getting, it's no wonder you hear complaints about them every now and then. Think I'd rather pay the extra cost and get one made by professional, real scope makers.

gregbradley · #10 14-09-2009, 01:47 PM

Make the factory fix it for free as lets face it the only reason you dissambled it was to correct their faulty workmanship in the first place.

There's a cost in business to putting out shonky products - its called
returns/refunds!

Greg.

dpastern (Dave Pastern) · #11 14-09-2009, 01:49 PM

Carl - again, I'm looking at the 10" deepsky instruments units...lot more expensive, but I think better build quality. Sadly, there's not a lot of info on them.

Dave

multiweb (Marc) · #12 14-09-2009, 01:55 PM

I know those scopes are cheap at $2k a pop for what they're supposed to deliver but man!... sounds like it's a bit of a "luck of the draw" if you're lucky to get a good one vs. a "chonky" one. mmhhh!... I'm going to stay on the side line for a long while now before committing to one of these "too good to be true?" .

Seeing far too many threads popping up about these.

gregbradley · #13 14-09-2009, 01:57 PM

I know a guy who uses one of them. He has some awesome images from them. They are Star Optics the same as RCOS used to use ( I don't think they use them anymore although I could be wrong).

They are also releasing a 14 inch soon but thats US$11,000. Cheap for a 14 inch though.

Greg.

Quote:

Originally Posted by dpastern

Carl - again, I'm looking at the 10" deepsky instruments units...lot more expensive, but I think better build quality. Sadly, there's not a lot of info on them.

Dave

Peter Ward · #14 14-09-2009, 03:48 PM

Quote:

Originally Posted by gregbradley

... the only reason you dissambled it was to correct their faulty workmanship in the first place.

There's a cost in business to putting out shonky products - its called
returns/refunds!

After the rave reviews of Paul's (& others) initial impressions, I am mystified why all of a sudden these scopes are being bagged.

If you have a major problem with a product, don't fiddle with it, call the vendor and arrange for a fix, or send it back!

But...there would not be a small claims divison in the country that would support a consumer who took it on themselves to dissasemble, then modify a product, then ask the manufacturer to fix it FOC

Would you do the same with a Breiting watch?

I personally own some pretty nice 'scopes. I was frankly amazed how well the GSO held up against these for imaging, it runs rings around any SCT I had previously owned (albeit in pre ARC, ACF, HD and any other alphabet soup versions).

Just my 2 cents worth...

renormalised (Carl) · #15 14-09-2009, 04:38 PM

I think what we're seeing here, Peter, is a big disparity between the quality of the scopes that seem to be coming out here. Some batches of the scopes are fantastic pieces of kit and other batches aren't worth using for boat anchors. I think, though, what you have to do is buy from a reputable dealer who will honour all warranty agreements and has a good reputation for service and sales of quality equipment. But getting back to scope quality, the consistency of the quality of build of many scopes coming from these Chinese/Taiwanese manufacturers is just not there. Sometimes they're great, at other times, not so great. Some factories are much better than others, though.

dpastern (Dave Pastern) · #16 14-09-2009, 04:42 PM

Quote:

Originally Posted by renormalised

I think what we're seeing here, Peter, is a big disparity between the quality of the scopes that seem to be coming out here. Some batches of the scopes are fantastic pieces of kit and other batches aren't worth using for boat anchors. I think, though, what you have to do is buy from a reputable dealer who will honour all warranty agreements and has a good reputation for service and sales of quality equipment. But getting back to scope quality, the consistency of the quality of build of many scopes coming from these Chinese/Taiwanese manufacturers is just not there. Sometimes they're great, at other times, not so great. Some factories are much better than others, though.

hear hear.

Dave

renormalised (Carl) · #17 14-09-2009, 04:57 PM

As good as some of these GSO RC's are turning out to be, I don't believe that the quality of manufacture is there yet to justify purchasing one, on the basis that you have a good chance of getting a dodgy piece of kit. If you want a quality RC, you have to be prepared to fork out good money for one. For instance, an OGS RC of the same size as the larger GSO (10") model costs between $24900 and $31500. An RCOS model of slightly larger size (12.5") is $21500. As they say, you get what you pay for. I think manufacturers such as GSO and other who are making these cheap RC's are only doing themselves and the RC design an injustice by slacking off with build quality. They'd be better off taking their time to create much better and more consistently built scopes. Even if the prices are higher for the sake of doing so. I'd rather pay $5000 for a good quality, well built and tested scope than $2000-$2500 for something I'd end up using as a door stop.

Peter Ward · #18 14-09-2009, 05:03 PM

Quote:

Originally Posted by renormalised

I think what we're seeing here, Peter, is a big disparity between the quality of the scopes that seem to be coming out here. ....

I don't know what the early models were like, as I haven't seen any. GSO say they now test the optics pre and post coating.

I have tested a number and would have been happy to own any, though I did seen some small sphercial error variations: to be expected in any mass produced optic. Anything gross I would send back.

Bright stars just outside a camera's FOV can cause stray reflections, but again even a 40K RCOS will do that.

I've found the build quality and consistency to be very good.

My only minor gripe would be the 10:1 focuser, the new ones have a linear bearing with minimal slop, but using the 10:1 reduction knob to lift a heavy camera, it would slip (the work around was to use the 1:1 uphill and 10:1 down)....but again, even my AP/feathertouch is a bugger to use with a STL+FWL+AO.

To be sure they are not an RCOS, but IMHO are not shabby either.

pmrid (Peter) · #19 14-09-2009, 05:51 PM

Quote:

Originally Posted by Peter Ward

But...there would not be a small claims divison in the country that would support a consumer who took it on themselves to dissasemble, then modify a product, then ask the manufacturer to fix it FOC

No. And I knew that when I opened the scope. However, perhaps it is not unfair to make the point that the reason I had to open the scope was to flock the baffle tube. The reason I had to flock the baffle tube were twofold:
(a) because it was sufficient defective to make it unusable in a range of situations; and
(b) the deal who sold it has simply chosen to do nothing about it - even to reply to my requests for help.
So I won't be submitting any claims to any tribunal. But I am also just as certain that not another dollar of mine will ever reach that dealer or that manufacturer.
I don't give the proverbial rat's whether the new models are the ducks guts of scopes. I'm dealing with the heap in front of me and it sucks.

Peter

Peter Ward · #20 14-09-2009, 06:21 PM

Quote:

Originally Posted by pmrid

.. I'm dealing with the heap in front of me and it sucks.

Peter

Pete, I understand your frustration.....and you should have had an acceptable remedy supplied by the vendor long before getting to this point.

All I'm saying is the very strong consumer rights you had prior to dis-assembling the optics have been severely weakened.

But a good optic isn't runied by being mis-aligned, it just needs to be re-aligned, I'd be banging on the vendor's door to get a hold of the required procedure, and if they refuse to help, GSO proably will. Hang in there