My TEC180 Flange Replacement

[PRejto]

This is a long story that hopefully is finally coming to a happy end. It started years ago with a then new camera, the SX-46. My results were optically disappointing (not to mention way too many electrical issues with the camera, now resolved) . I simply could not achieve a flat enough field even after replacing several poorly made adapters with superior adapters made by Joshua Bunn. so, 2-3 years ago I entered a long period of not imaging whilst building a house and observatory in Rylstone. After the observatory was commissioned it was apparent that I had to find a better way forward with my TEC180 and the SX-46. Josh offered to take the entire optical train and rework it. This included a Gemini rotator, the large SX filter wheel with a heavy OAG due to a motorised focuser, TEC flattener, and the camera. The proposal was to build a custom cage that would allow for back-focus changes, tilt, and lateral adjustment for an off center CCD. The work included new adapters, a counterweight to offset the SX FW, and a reworking of the FW strength.This took some time!

Finally the equipment came back and Josh did a superb job! The cage is totally unique and custom designed (see photos). I then had the daunting task of learning NINA and HocusFocus which took quite some time. Finally I got there and had a beautifully flat field. Josh was very patient during this process! I was momentarily "happy" and had the audacity to believe I might once again actually image. But, no, of course not. In this crazy hobby I am a magnet for problems and it only took a couple of slews to discover that all my hard fought adjustments for tilt were just gone. Yikes
.
So, the search for "where is something moving" began. In previous attempts to find problems Josh had suggested a steel bar and dial indicator, so these went back on the OTA. I started measuring gravitational effects on the imaging train and was pretty shocked by the amount I was measuring near the camera. I expected some from the rotator, but certainly not that much! The imaging train was/is long and quite heavy (7.5 kg at about 37 cm from the flange), but within the specs for the Optec Gemini. Imagine my surprise when I discovered that the actual flange was moving on the OTA! How could this be on a quality OTA like the TEC180? I measured 10-30 microns of movement at the flange which translates to ~200-500 microns at the camera. After posting on the TEC user group I learned that I couldn't get a new flange from Yuri as the newer TEC180s use a different size tube and consequently the new flange will not fit. And, it's rivited on.

After much back and forth with Josh we came up with the mother of all flanges, which I finally completed the installation of today. It has an outer and an inner screw on piece and clamps the tube from both sides. It is massively bigger and stronger than the original! It's quite hard to imagine this flange could actually move. It wasn't easy to install given the drilling of 12 holes that had to align perfectly.

The project is now only partly finished because we decided that there also had to be some way to shorten the optical train that hangs on the rotator. The only way this could happen would be to locate the flattener inside the Gemini and this also means that the TEC flattener has to be extensively modified. It now has threads running the length of the flattener body which will screw inside the rotator. I've asked Josh to make an adapter so the flattener can also be used in the original configuration. As these flatteners are not made anymore this extra part seems necessary even if I won't be using it this way in the foreseeable future. The reduced path length to achieve focus will be made up by a very heavy duty extension tube located before the rotator.

Josh is just finishing up these extra adapters and modifications. When I have it all assembled again I will be getting out the trusty dial indicator. I expect a vast improvement. Fingers crossed that this time things finally work as expected. It's only going on 4 years....

A huge thanks to Josh for exceptional work!

Peter

You can compare the original flange with the new flange in the attached photos which also show the original long heavy image train and the custom tilt cage.*

[croweater]

I like it Peter. We are lucky on this site to have easy access to someone so highly skilled. An added bonus is Joshua being a pleasure to deal with. Best of luck with your endeavors.
Cheers, Richard.

[Leo.G]

That's been quite the headache from the sound of things Peter.
It's unbelievable that something as high end as the TEC180 would suffer from shift of all places at the flange. To my stupid brain I'd guess the mount holes which held the flange to the tube were oversized to make installation somewhat easier but allowing for the heavy image train to pull it around. Is it a steel or aluminium tube?

I'd expect something like that from my second hand Skywatcher 152 achromat, not something that I could only ever dream of being able to own.
I hope you have it all sorted and I'd love to see the resulting images!


As for Joshua, I really want to get his focuser adaptor for my GSO RC8 but haven't had the finances (and it's only a couple of hundred dollars, not high end pricing (actually extremely cheap)), one day. I've seen much of his work shown here, what an amazingly skilled fellow he is (Along with Stefan Buda, his projects and results are amazing too), the only baffling part with the focus adapter is could I collimate the RC8, I see so many negative mentions of the procedure.

[Joshua Bunn]

What a great write up Peter.

It has sure been a long process for you getting your rig working, but you keep persisting, so well done to you!
Thanks Rick and Leo! Leo, do you mean will you be able to collimate your GSO once my adapter is installed?

[PRejto]

Leo, It was certaily a surprise to me too. However, in TEC's defense, my OTA is pretty old and I highly doubt that when it was made anyone would have though, or even been able, to add such weight behind the flange. Their design is updated now so I don't think my issues would apply to their newer model. The older models, possibly yes. I saw no evidence of enlarged holes removing the original flange. I think the inner portion was/is just too shallow to hold that much weight. 30 microns isn't a lot but does amplify with a long imaging train.

P

[Leo.G]

Errors are always accumulative.
Age and varying weight extensions/loads over the years would exaggerate the problem, I didn't think of that.
It must be a hard trade off for manufacturers too because they can't predict newer, larger imaging device weights and future needs. Add in the fact we always push our gear to new limits to capture that bit more data/detail..........

[strongmanmike]

Great work you guys, Josh you are a beast of a machinist/fabricator, that's for bluudy sure! :prey2: Looking forward to some new images out of that awesome scope Pete, now bionic! :eyepop:

Mike

[Leo.G]

I didn't mean an incapacity to collimate it once I do eventually get the adaptor when I have the funds, I mean overall collimation of the scope, from what I've read it can be a nightmare, add in poor eyesight and the fact after I've read instructions I've forgotten them by the time I've selected the tools to do the job.
My memory never used to be like that, in fact I have qualifications in a number of fields (electronics engineering, fabrication engineering, fitting and machining, hydraulics and pneumatics, IT, just to name a few (lots of years on disability and had to keep my brain sharp and always had an insatiable thirst for knowledge and an uncanny ability to solve any problem from an engineers perspective from a very young age)).
I got distinctions across the board, always top of my classes and years from primary school right through all of my studies because once I'd seen/heard/read something it was instant recall for life, or till I turned 50 anyway. Going from an eidetic memory to a failing memory has been quite the shock to my system. I could read a book on basically anything and go and do it and do it well.

I would have liked to see a little more follow up from Mike in Brisbane, I was extremely interested in the adaptor, I still am when finances permit.
At the moment I'm battling a sudden rapid decline in health I have to discuss with my doc when I see him in 2 weeks, it could be hernia, could be bowel related and I've hardly moved all day except to throw up.
I never get sick in my life!
Well, I've been sick in the head for well over 50 years, chronic migraines on a daily basis since childhood but today I was very sick. I don't like it!

[Joshua Bunn]

Aha yes, I see Leo. Collimating the GSO RC is made easier with my adapter addition, since the imaging train in no longer pulling on the primary mirror. On another note, I am sorry to hear about your health issues, I cant imagine daily migraines.



Cheers Strong man Mike, but I mean, you know me ... :D

[Leo.G]

Thanks Joshua, had it daily for well over 50 years, it is my living hell and why I NEVER make plans. I'll know what I'm doing in an hour in exactly an hour. One session can last day and night exceeding 3 months.

[gregbradley]

Wow, that is quite a story.
Sorry to hear your troubles.
I remember on the TEC forum where Yuri measured flex on the Feathertouch 3.5 inch focuser and it was less when the focuser was upside down, ie. the focus knobs are on the higher side.

So I used to image with it in that position. I don't think it made a lot of difference but it was measurable.

I imagine a 7.5kg and long imaging train is outside the specs for the scope.
I got a perfectly flat field with the flattener, adapters, MMOAG and FLI Proline 16803 (quite heavy). That was probably 4.5kg perhaps a tad more.

Greg.

[Leo.G]

7.5Kg is a lot of weight, was that a big CCD camera?
Stupid question, you've listed the FLI.

[PRejto]

Hi Leo and Greg,

Yes, 7.5kg is too big!

The Gemini rotator is quite heavy to start with. Then adding the Starlight Xpress SX -46 and large FW add quite a lot, plus Josh's clever tilt cage and conterweight and reinforcement of the flexing SX FW, plus a featherTouch 1.25" motorized focuser on the guide camera, produced a weight the original flange just couldn't cope with. It is a pity it took so long for me to think of it as a contributor to the problem. It's just something one assumes will not be a problem!

The Gemini remains the weakest link in the system. Hopefully moving the flattener inside the focuser will reduce the moment of all this gear enough tio finally get this under control.

P

[Leo.G]

I have not played with expensive equipment and have heard of rotators but never seen one. Does it sit close to the focuser or much farther back where the camera is?
I understand moving heavier objects as far forward doesn't change the overall weight but it may alleviate some of the flexing?
But I'd be betting you have already looked into every possible combination of connection.
I hope you get it sorted!

[PRejto]

Leo,

Take a look at photo #2 in the first post. The Gemini is a focuser and rotator in one unit. It is sitting right next to the flange. The flattener is attached directly to the rotator. The idea is to move the flattener inside the rotator, but then extend the rotator out from the flange an equal distance with a very heavy duty extension tube. Make sense?

P

[Leo.G]

Thanks Peter, I looked up the Gemini but only saw a rotator, didn't go through their gear and as I have seen the rotators selling here used I assumed it was a slightly larger (considerably larger) version. I was wondering why it wasn't part of the focuser, it's what I've always done with My William Optics focusers in preference to moving the camera (or rotate the image).


OK, that makes sense, the only two items in the image I could positively identify was a large filter wheel and a magnetic base dial gauge (and the 25^2mm square hollow section, lol).


Is it going to be a hard task to move the flattener into the rotator?


I have my extensions machined to my specs for my toy gear but they do add a level of weight to the rig but I do regularly check the precise weight of everything I'm hanging off the back, especially playing with smaller gear with a high degree of slop in the cheaper focusers like my 5" (130mm) Celestron Newt but it's been shimmed up with brass and considerably better than new I'd suspect. Plus I can rotate the tube so my image train is closer to vertical, not so easy on any refractor, especially not on that monster you have there.
The images must be incredible.

[gregbradley]

Is this a remote scope?

I never used a rotator as the whole focuser can be easily rotated like an AP scope. But if it's remotely controlled then that is a different story.

I personally have never used a rotator. Sometimes it would be handy but of course every time you rotate you need a new set of flats so it's extra work.

Greg.

[Leo.G]

Pardon my ignorance but why the new set of flats with rotation or is that for any marks/errors in the optics?
I only play with little toys, nothing fancy.

[PRejto]

Hi Greg,

Yes, the observatory is in Rylstone, but totally automated. I can image from inside the house, or Los Angeles. It's very cool.

Leo, It's best practice to shoot new flats on rotation, Whilst the majority of dirt is on the filters and CCD/CMOS cover, the light cone may or may not be symmetrical, even with a refractor. And, on a reflector, I suppose the vanes are in a different position upon rotation.

P

[Leo.G]

I realised after I posted, my imaging is primarily done with a FF Nikon and once it's attached and focused I never rotate it. Though on the odd occasion I've chosen a different target and removed the camera while slewing and locating /centring the target and I have done separate flats, I just haven't done that too often.
As mentioned, no permanent location and small toy equipment, nothing as serious and you and Greg.