Ritchey Chretiens and collimation

[pmrid]

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]

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]

Here is the RCOS writeup.

Only problem is they use a Takahashi Collimation scope.

http://www.rcopticalsystems.com/support/images/rcos_alignment_collimation.pdf

Greg.

[Doomsayer]

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]

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]

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]

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]

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]

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]

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]

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]

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?" . :confuse3:Seeing far too many threads popping up about these.

[gregbradley]

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.

[Peter Ward]

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

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 :doh:

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]

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]

hear hear.

Dave

[renormalised]

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]

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]

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]

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 :)

[rat156]

I think I have to agree with Peter Ward here.

To compare the GSO RCs with RCOS type instruments is like comparing Hyundais to Ferraris. Both are functional cars, but there is a reason people pay $250k for a Ferrari.

Now the GSO RC that I have needs collimation, but this is generally true of all mirror design telescopes that have been shipped half way round the world.

I have found the baffling to be adequate, bright stars to flare when slightly out of the FOV of my SBig. The focuser is really the only thing I'd quibble about, but I have a really heavy imaging rig. They are pretty good value for the price.

Some of the first series of these scopes had some problems, the distributor should have done something to help along the early adopters who have paid a premium for something that's now been superceded.

I don't know where the negativity towards these scopes comes from, they're cheap allright, but they're good too. It'd be interesting to review the posts about the ED80, to see if they follow a similar thread?

Cheers
Stuart

[renormalised]

Well, there's one way to see what's happening here...everyone that owns a GSO RC scope, post here when they bought it, so we know if it's an early or later one. Then we can see what's what, and determine the problem(s).

[Peter Ward]

...trying to make me feel glum :) ..finally picking up my twin plate clutch this week! :cool:

[pmrid]

Mine was the first one sold by the Sydney dealer whose name is forever stricken from my lips and credit card. It was sold to another iiS member from whom I bought it. So mine is definitely an 'early' model. Early Adopters of the world unite!!
Peter

[marki]

Wow, usually threads like this are based around Meade or MS bashing :P. From the little experience I have had with these scopes (helping Trevor W with his early version on occassion) they appear to be good value for money bar the issue with reflections on SOME OBJECTS. They are not overly difficult to collimate (on par with my ACF) and deliver good views although to my eye the ACF images are brighter (Probably more to do with my scope having an extra 2" of aperture and using 2 " rather then 1.25"diagonals). If I had any gripe with this scope it would pertain to the hassle of fluffing around with all those extension tubes to get different setups to focus, very annoying. Although I do not envy your position Peter you knew the risks before taking the scope apart and you have paid the price (which is simply uncertainty as to what you must do next). You cannot blame GSO for this. The optics have been aligned before so they certainly can be done again, you just have to find out how. As for the focuser, Trevor replaced his with a Moonlite and it's as solid as a house brick.

Mark

[TrevorW]

In defence of the scope whether it needs it or not:

Paul and myself as far as I'm aware have both taken the scope apart without any problem I followed Pauls instructions

The baffle tube easily unscrewed from the primary no movement whatsoever of the primary



A Ronchi test conducted by MArki showed a nicely formed mirror

Once collimated they produce exceptional images

For the price at the moment they are the cheapest RC on the market

Make sure everything is square and then is shouldn't be too difficult for someone experienced to collimate. Collimating with two heads didn't take long

PS: like the rest of us you've blown your warranty by taking it apart.

All the best

[coldspace]

People need to start coming up with some sujestions for Peter to go down to get his scope back together and colimated instead of all the comments like you have blown your warranty, and this and that.

Is there someone in OZ that he could send his scope to for a small fee to get re-aligned?
If not, then what is he able to do or is it just a piece of rubbish now, surley not.
Its a pity the dealer involved can't be named and shamed in the treatment of this customer in the first place.

If i were you Peter, go to the cloudy nights site and do some searching and ask some questions there as you may find out a positive outcome. I have always had excellent responses to my many questions regarding things over the last few years, so I am sure you will.
I know your frustrations that you are going through as I have been down this path but not on astro gear yet.

Who are the other GSO dealers here in OZ, In buisiness myself I have helped out a few customers here and there with problems that was caused by the opposition and I tell you what it brings in at least 10% of our buisiness from good word ,if they are smart they will try and help you out either getting your scope fixed or sent back to GSO via them ( you pay shipping) to get it re-aligned and then you can tell all of us about this dealers wonderfull service and we will all possibly spend money with them instead of the other mobs.
If no luck on this then PM me and I will talk to a friend who works in the industry and has ties with GSO and maybe can get some help that way, don't stress yet something surley can be done.

Good luck with it mate.

Regards Matt.

[marki]

I forgot about the ronchi test. Trevor's mirror was as smooth as showing no signs of the predicted roughness. There was very slight (and I mean very slight) over correction on the outer edge. I would be happy to have this mirror in my scope.

Mark

[dpastern]

And this is exactly why I feel it's fair game to bash these retailers. Let's look at it this way - newbies who do some pre sales research will not get realistic and honest feedback on retailers when forums are censoring truthful posts about retailers and their lack of support to customers. Said newbie sees nothing but good reviews, because the bad reviews have been removed from forums due to forum owners being worried about legal action, and makes a mistake and buys from said retailers. Newbie is not happy when something goes wrong, wonders why he can't find any reports of crap support from said retailer when he researches etc. It's a disservice to us - the customer. Retailer 1, customer 0. Not very good imho. Any retailer who threatens legal action against a forum should have their IP address banned from viewing the forum site - it isn't that hard to do.

Dave

[marki]

Matt I agree with you that anyone who can help Peter with his dilema should jump in as soon as possible. Comments about user folly are also valid as threads like this can build a bad reputation for a product when it is not deserved.

Peter good luck hope you find a solution very soon.

Mark

[Peter Ward]

Peter....while it's not my problem, you might want to e-mail me directly.

I'll see what I can find out directly from GSO to get a bit of local support/knowledge, which will not doubt help others in time as well.

[dpastern]

Well, let's look at the facts. Said retailer wouldn't touch the problem, despite numerous attempts to contact them by the OP. That's in breach of the trade practices act right there. GSO has no official footing in Australia, so they're out of the window. Other retailers are not obliged to support the product, since it wasn't bought from them.

Now - the NSW department of fair trading usually goes to problem resolution first - this is not *legally* binding, and from my experience, is usually biased towards the manufacturer/retailer. If you don't like that outcome, you can take it to the tribunal - there's $100+, non refundable I might add for that right. That decision is legally binding, and generally doesn't side with the consumer either (numbers wise). That leaves legal action, which is costly and no guarantee of winning, even if you have a decent case. Again, the courts tend to side with the biggest lawyers, and they're usually owned by businesses, not the consumers. The whole system stinks.

Dave

[marki]

Onya Mr Ward :thumbsup:.

Mark

[DavidU]

Pete Pmrid, where are the photo's you speak of. I would like to see them.

[coldspace]

This is what we are looking for, a possible solution to a big problem,
and helping a fellow astro mate out as well.
Good on you, for even if you can't help directly a little direction for Peter can go along way:thumbsup:.

Let us all know Peter how you go and who helps you out.

Matt.

[dpastern]

Yeah, good on you Peter for offering to try and help Peter. That's very kind of you, and other retailers should take note of the customer service being offered.

Dave

[JethroB76]

What warranty can you expect on a secondhand telescope?

[pmrid]

Thank you Matt and Peter in particular. I will email Peter off-site as he has suggested but in case there is someone else out there who now, or later has a similar problem and needs to recollimate the primary and secondary on a GSO RC, I note that I did find a discussion in CN where the technique of collimation was discussed. It was in the context of Astro-Tech scopes which are, effectively, GSO. The suggestion that was offerd there was to use a Cheshire without crosshairs or a pinhole in a film canister to do a visual alignment of the reflection of the baffle tube in the secondary by adjusting the push-pull screws on the back of the scope and then, using a laser collimator tha projects a hologram to cast the shadow of the secondary onto a flat surface against a grid pattern so that the mechanical alignment of the secondary can be confirmed - i.e. making sure it is algned with the optical axis; then, using a dot-point laser collimator into the eyepiece holder, move the secondary mirror until the return dot was centrally placed on it - the laser folded back on itself.
An interesting phenomenon discussed there without a solution and that I also encountered was that although there is no physical connection between the secondary and the primary, when you adjust the secondary, the initial line-up of the baffle tube has shifted and you have to loop back to step 1 again. Not sure why this is so, but after half a dozen attempts at this today I had to pronounce myself knackered and ready for something else.
I will revisit this thread with a more detailed description if a successful technique emerges out of this unfortunate experience.

Peter

[pmrid]

David, the photos referred to were taken from a short piece written by Paul Haese illustrating the technique for flocking the baffle tube on an RC. When I drafted that posting, I incorporated a couple of Pauls photos but they did not carry across to the posting when I did a cut-and-past from my draft which was done in Word. I should have edited references to them out of my posting. However, if you would like, Paul's article was well written and descriptive. You'll probably pick it up on a google search or I can email a copy to you. At the moment I don't remember where I actually got it from.
Peter

[erick]

I think this is it:- http://paulhaese.net/gsobaffleflocking.html

[gregbradley]

I removed the primary from my RCOS 12.5 inch once and cleaned it and refitted it and recollimated it. It wasn't that hard.

If you haven't touched the secondary then it consists of:

1. Aligning the primary and secondary index marks (mine had a paint mark on the side of the primary and secondary so you rotate the primary's mark to line up with the secondary's mark.

2. You can do something as simple as a plastic cap with a hole in the centre that fits in the visual back. Now line up the spider cross so that the secondary and primary form concentric circles.

3. I used a Tak collimation scope here to get this alignment very accurate.

4. Final tweak using a star (I didn't do much here as it was pretty close and small adjustments made a pretty large difference.).

Also following a thread on another RC site (A&M RCs) they flocked the secondary mirror light shroud to stop unwanted reflections from bright stars just outside the range of the image.

You can also download a free trial of CCD Inspector which has a live collimation tool to get it exact using a CCD camera.

As far as shims etc go I presume they were put there to ensure the primary was square to the tube. Perhaps the back of the mirror is not
even and so it needed shimming. So put it in and adjust the shims so it is stable and appears square perhaps a cheap laser collimator may be helpful there too.

I imagine the shims also help put the collimation adjustment into the correct range of the adjustment screws in the case where it is quite a ways off.

Perhaps this helps.

Collimation isn't really that difficult, you just need a set of instructions.
Try the above and see how you go.

There was also the link I posted to the RCOS collimation instructions. They were the ones I used. When you get up to the point where you need a Tak collimating scope perhaps you can subsitute a cheap laser collimator. It saved my bacon when collimating a fast F4 200mm Vixen that was difficult to collimate before I used the cheapie Antares laser collimator from Scope Stuff (www.scopestuff.com (http://www.scopestuff.com)).

You know there's no way around it for any RC or compound scope owner, learning how to collimate is a basic skill that you're going to have to confront learning at some point as the fact is compound scopes collimation will not always hold, especially if you travel with it. Admittedly adjusting it from parts is going to be the hardest.


Greg.

[pmrid]

Greg, that's extremely good of you. Allow me to thank you. I will see how those suggestions pan out over the next few nights.
Peter

[sjastro]

I'm dubious about the effectiveness of CCD Inspector as a collimation tool.
I use it to monitor FWHM for luminance imaging. I find the collimation value can vary 50-100% from exposure to exposure which suggests the procedure is seeing dependent.

Steven

[Paul Haese]

Having thought on this for a while and read through the thread again I am inclined to think that you can sort this collimation as Greg has suggested. Some time ago I came across a collimation PDf for an RCOS. A chap did exactly what Greg did and we all will at some point to clean the mirror. The adjustment screws are there on the back and it would be unreasonable not to expect the mirror would need cleaning one day.

My suggestion is this:

Consider buying a tak collimation scope or borrowing one. A chap I know here in SA might loan me one when I need to do mine, however I think I need one myself; there might be someone in your neck of the woods that has one too. It's all part of owning an RC. Take your time and pull the scope apart again. This time just inspect the entire mirror bottom. Look for registration marks, there is likely to be some and take a bit of look at the secondary but don't take it out of the tube. Just look for the same marks as Greg suggested. You should also take a look around for the other mystery shim. It might still be there or make sure you seated everything correctly on the first reassemble. You might have misaligned something and hence the reason for the wobble. I am inclined to think that this is the likely cause of the wobble, but I am not there. Once you have it altogether again use a Cheshire and look for alignment. I have looked through the back of my OTA with this and noted it was perfectly aligned and this would be a good tool to have too. If you have not touched the bottom screws don't unless you really have no other option but to move them. These screws should be considered as being your base line. Rotate the mirror until your secondary is centered perfectly if you cannot find any alignment marks. If there is alignment marks use the shims to center the secondary. This is going to take some time and you need to work on a kitchen table or somewhere comfortable. Once you have it all centered then prepare for a star collimation on a clear night.

It might not suit everyone but try to keep this in mind. Collimation is often required for folded optics. It is a skill that anyone can learn and when you get this sorted you will have a sense of accomplishment.

For people who feel it is necessary to make the thread about blame, please bear in mind that any folded telescope with optics exposed to the open will require the mirror being removed at least a few times in its life time. All RCOS telescopes have front and rear collimation screws as does the GSO from what I can gather. If the factory got it into collimation before then so can the average amateur. This is a hobby where you need to maintain equipment and adjust it if necessary. It is also a hobby that requires patience most of the time. Something we can all learn more of most of the time.

Peter this is achievable and you can do it. I would ask you post images of the entire back of the OTA disassembled. It could help us find the marks and help you. I would also urge you to contact a large astro society. ASSA holds collimation clinics and has lots of guys who know how to put equipment back together again, we even have a few opticians; maybe your society does too. We did this for years before commercial telescopes were available, we all made telescopes and pulled them apart and put them back together. If you lived near me I would come and take a look myself. I am not afraid to pull apart equipment and put it back together.

Post those images thanks.:)

[pmrid]

Paul, I am indebted to you and other contributors who have proffered some practical advice - all of which I receive in the spirit in which it is given. Thank you.
Peter

[DavidU]

Some pics would help Pete.
You can do it !

[gregbradley]

Here's a link to a thread in Cloudynights where a guy describes some of the steps he took to collimate his AT8RC.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3178132/page/0/view/collapsed/sb/5/o/all/fpart/1

You could also contact him for further advice.

Cheers,

Greg.

[catseyeman]

I read this as you use a reference spot placed on the "Secondary" for a visual queue to generate the autocollimator reflections. Is that correct?