TOA130 colimation assistance

[tempestwizz (Brian)]

Aware of all the learned advice saying that a TOA130 can only be successfully collimating by Tak in their factory, I am attempting the impossible.
For a number of reasons is is just not economically or physically feasible to ship the scope from my current location without a strong chance of damage and or loss, plus horrendous fees.

I am seeking input from any TOA130 owners who believe their scope is well collimated, and who may have a laser collimating tool such as a Howie Glatter.

Firstly, I would like confirmation that the contrast of the airy rings is the same either side of focus.
And secondly, with a laser beam centred in the eyepiece holder, that the major internal reflection is seen to be at the centre of the laser. Like for a collimated Newtonian.

I purchased my scope second hand a number of years back, and when it arrived, the front element was rattling around. Hoping that the set screws hadn’t moved, I tightened the larger retaining screws and hoped for the best. It sort of worked. I got sidetracked from resolving the issue with more new toys, and a lot of travel for work, so I didn’t get back to it until now. Unfortunately I’ve also relocated to the wilds of Laos and don’t have access to the same level of shopping and shipping any longer.
If I can’t fix it, I’m no worse off really, if I can, then it is an ideal scope for this part of the world.

I spent some hours with the scope yesterday and am climbing the learning curve of how things work.
I’ve made myself an artificial Star to check the airy Discs and have a Howie Glatter laser collimater that works well.

On first view, I noted that there was a sort of airy disc on the inside of focus that turned to mush on the outside of focus. (Using the word focus loosely here).
With the laser inserted, I noted the reflected laser points from the various lens surfaces were scattered all over the place on the collimater.

I learnt that one set of adjusting screws affected all the reflected dots, and that the other only affected some.

My suspicion is that the inner of the three elements is fixed solid in the tube and cannot be adjusted. The major reflection from it is strait back into the laser and cannot be identified.

The first set of adjusting screws (which are the ones set further into the scope) seem to move the two outer elements together.
The second set move the two outer elements with respect to each other.

I adjusted the second set of screws to place the brighter dot that moved with it over the brighter dot that wasnt moving. With the other set of screws, I moved the two superimposed brighter dots to the centre of the incoming laser beam.

It couldn’t be that easy. And, it wasn’t,

Checking the airy Discs, they were terrible, but there was some form in them.

With a lot of iterations, viewing the airy disc I managed to form a circular airy disc that shows either side of focus.
The airy disc on the outside of focus is still quite faint, but a disc now, and not mush.
I checked with the laser again, but the major dot was no longer in the center. Every attempt at moving it back toward the centre messed up the airy discs.

Hence my questions above.

After a night’s sleep (or maybe during it) I now realise that I have been adjusting basically only the angular orientation of the elements.

By stepping all three set screws either in, or out together, I have the ability to move the inter-element spacing while still maintaining the angular alignment.

So that’s where I’m at now.

Grateful for advice on the questions above, and any other feedback.

Cheers.

[Logieberra (Logan)]

Brian, I hope you are well mate. Contact "Art" at Texas Nautical Repair (TNR) in USA. He can supply the advice and PDF instructions that you need.

[Exfso (Peter)]

Seriously having had a TOA130 that was out, you really do need the pros to re-collimate. I sent mine to a Sydney mob who were recommended by the Aust distributor a few years back and they absolutely trashed it. It is no wonder they went down the gurglar They really did not have a clue, I ended sending it back to Takahashi who were astounded at the mess the whole cell was in after these clowns wrecked it. The whole front end needed re-building. I had mine done under insurance, so it was not too bad financially. Art is the man to contact at TNR, I was in touch with him once and he and his mate were extremely helpful.

[garymck (Gary)]

Hope this helps:

http://www.celestialportraits.com/cp...on-toa130.html

cheers
Gary

[sharpiel]

Gary,

That article refers to a number of attached diagrams...but they don't seem to be included. Have you seen the full document including the referenced diagrams?

[garymck (Gary)]

Hi Sharpiel,

had that link from ages ago, (when I was a Tak owner) can't remember if the pics were there or not. There is an email at the bottom of the page, so I'd suggest contacting the page owner....

cheers
Gary

[Merlin66 (Ken)]

Brian,
Just a comment...

Did the laser hit the centre of the lens before you did anything??

This test is usually only used to align the focuser with the optical axis.

I've successfully used a Cheshire eyepiece to re-collimate a doublet - See Suiter's "Star testing", p 121

[tempestwizz (Brian)]

Thanks for the article Gary, I’ve sent an email to the page owner.
I’ll absorb the contents meanwhile.

Merlin, when I first used the laser down the focuser, the reflections were scattered.
After my most recent attempts, I have the reflected laser to a single spot, however it is not back in the centre of the focuser. Attempts to ‘move’ the laser back to the centre seem to throw out the airy Discs that I currently have.
Live test last night showed that my stars aren’t bad, but have what looks like a small flare in the direction that the laser beam was off centre.
More adjustment required.

Cheers

[Merlin66 (Ken)]

Brian,
Not sure what you mean by:
""I have the reflected laser to a single spot, however it is not back in the centre of the focuser""

It's more usual to adjust the focuser relative to the OTA to align the laser spot on the centre of the objective. A greaseproof paper with centre marked, across the front of the objective will confirm the alignment.

[tempestwizz (Brian)]

Sorry, perhaps I did not explain well. When I adjust the angular position of the elements, the internal reflections from a laser located in the focuser bounce around and some come back to the focuser, when viewed from the front of the scope.
I have a couple of times now concentrated on getting those internal reflections to all meet up at a single spot in near the centre of the focuser, and then adjust whatever was necessary to move that single reflected spot back to the centre of the focuser (right down the throat of the laser producing the beam, as for a Newtonian scope)
When I have attempted this, I cannot seem to get all the reflections back to a single point. I can merge what initially starts out as two dots, one way brighter than the other,but as I make adjustments to shift those two merged points back to the centre of the focuser, another faint dot becomes visible. And it is not at the centre.
If I check the airy pattern when the laser dots (but not the new faint one)are at the centre, the Discs are rubbish and way off.

If I readjust and get the airy patterns to look hallways reasonable, and check with the laser again, the reflected dot, and its faint companion is way off the centre.

I’m guessing that when it is right, all will come together, airy Discs and the central reflection.

[Merlin66 (Ken)]

I think you’re using the wrong tool for the wrong job.
The laser is for alignment, not for collimation.
You really need to use the Cheshire eyepiece. Elements at the rear will give brighter disks/ doughnuts, fainter for other elements towards the objective.

[tempestwizz (Brian)]

Hi Ken, sorry to disagree, but the Howie Glatter collimation works just the same as a Cheshire. Difference is the Cheshire has the 45 degree cutout to view from the focuser end whereas the HG has a white plate on its front face, and you view the reflections through the front of the scope. In any case I tried my Cheshire in case I was missing something but it gives the same result.

I’ve not had confirmation from any source that the rear element of the TOA assembly is fixed in the OTA. I’ve been working on the assumption that it is, and that the two sets of adjusting screws work only on the front two elements.
But looking closely at the assembly today, it appeared as though all three elements were moving with one set of screws. I can’t fathom how you can individually adjust three elements with only two sets of screws. I’d be grateful if someone could enlighten me on that.
After another day of fiddling about moving one set of adjusting screws through ther range of motion, I think I have found a sweeter spot than I’ve seen before. Airy Discs balanced on either side of focus. But, the point of focus is a little vague, and my laser reflection is back where it was at my last two attempts, and not in the centre where is expect.
I’ll try it on some real stars a little later tonight.

[Merlin66 (Ken)]

Brian,
OK.
My comments were based on a laser pointer collimator....I overlooked the reference to the Howie Glatter. I've no experience with this collimator.

[thebonz (John)]

I looked into the toa collimation some time back and I can recall that one set of screws tilts the whole cell and the other set tilts and sets the distance from the single element against the other 2 elements.
There was a hard to find web page that explained it all.
Cheers. John

[sharpiel]

Originally Posted by thebonz

I looked into the toa collimation some time back and I can recall that one set of screws tilts the whole cell and the other set tilts and sets the distance from the single element against the other 2 elements.
There was a hard to find web page that explained it all.
Cheers. John

John...any chance you'd be able to re-find that web page?

[thebonz (John)]

One website is celestialportraites.com It has some info but the diagrams are missing. I cannot find the lens cell diagrams.
Cheers

[tempestwizz (Brian)]

Thanks guys; the bonz is right. I worked it out for myself today.
Now need to work out how critical the spacing of the front element from the other two fixed ones is in the scheme of things.
First trial didn’t give even airy Discs either side of focus.
Trial and error if all else fails.

[sharpiel]

Originally Posted by tempestwizz

Thanks guys; the bonz is right. I worked it out for myself today.
Now need to work out how critical the spacing of the front element from the other two fixed ones is in the scheme of things.
First trial didn’t give even airy Discs either side of focus.
Trial and error if all else fails.

Keep us updated. I have a toa and would love access to all the literature and experience you gain from your experiments. Just in case one day...Sometimes things go bump in the night....

[thebonz (John)]

I am also very interested in the end results. I can recall that the distance between the 2 sets of elements may be critical to eliminate CA. If I was to do it, I would use a step approach like you are doing. I have had great success collimating doublets with the Takahashi collimation tool that is an advanced Cheshire eyepiece.
Some photos of lens cell and steps would be invaluable

[sharpiel]

Lewis sent me this link once. It's in Japanese but at pp 18, 19, 20 there are some collimation diagrams...not sure how you'd translate it.

Perhaps it will help...

http://www.takahashijapan.com/ct-pro...f/TOA-150B.pdf