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  #1  
Old 21-01-2018, 11:26 PM
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tempestwizz (Brian)
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Overview of TOA130 optical assembly

Frustrated in my attempts to obtain fine collimation of my TOA, I disassembled the optical assembly to learn how it is constructed in the hope that with this understanding I will now be able to collimate.

Removal and disassembly is surprisingly simple.

Firstly I removed the lens hood. In my version it simply unscrews from the retaining ring. (Removal of the hood is not absolutely necessary, but it opens up the assembly to allow gripping while removing screws)

The TOA has two sets of adjusting screws visible from the front. One set is recessed into the face plate, and the other set sits on the front.
The adjusting screws themselves are in sets of three, with one larger screw in the centre, and two smaller screws either side. They operate in a push-pull arrangement. The two smaller screw each pushing, and the larger screw pulling.

Removal of the three larger screws that are inset into the assembly release the whole lens assembly which can be lifted out for inspection. I made note of the orientation prior to removal.

All three glass elements are contained in this assembly.

The innermost two lenses are fixed. There is no individual adjustment for them.
Hence, the adjusting screws that were just removed, allow only adjustment of the assembly as a whole.

The other set of adjusting screws affect the front element with respect to the other two fixed elements. If the larger screws are removed, the front lens element can be separated from the assembly holding the other two elements.


(In my case, after removal I noted that my rear element was loose in the housing. The lens retaining ring had loosened by about a turn and a half. After retightening, I put a drop of Loctite onto the thread.)

So now, Iím guessing that I should replace just the assembly with the two rear elements and align it via the laser reflection from focuser with the inner set of adjusting screws.
Then, replace the front element and align it to centralise laser reflections.
Then use an artificial Star to fine tune the airy patterns. This is indeed fine tuning, as 1/10 turn makes a huge change to the patterns.

What I am not sure about is if the spacing between the front element and the other two has any affect on CA. If so, I may have to step the spacing of the front element in and out by trial and error to minimise CA.

I hope this info can be of assistance to others. Iíve not been able to locate any information on the physical construction of the TOA assembly anywhere else.
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  #2  
Old 22-01-2018, 10:00 PM
sharpiel (Les)
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Any pictures?
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  #3  
Old 22-01-2018, 11:01 PM
Wavytone
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To be honest this reads like you have no idea what you are doing, you've mucked up your scope - and from here on in you're guessing.

Better to send it to someone who knows how to fix it before you go any further. Otherwise its basically stuffed.
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  #4  
Old 22-01-2018, 11:08 PM
bigjoe (Joe)
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This is getting scary.
Hope it turns out well.
bigjoe.
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  #5  
Old 23-01-2018, 08:41 AM
sharpiel (Les)
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Quote:
Originally Posted by Wavytone View Post
To be honest this reads like you have no idea what you are doing, you've mucked up your scope - and from here on in you're guessing.

Better to send it to someone who knows how to fix it before you go any further. Otherwise its basically stuffed.
Well Wavey, he's already into it now and has explained that a return to a recollimation expert wasn't affordable/feasible as first option. So credit to him for having a go at something that terrifies other TOA owners (including me).

However if I drop mine I prolly couldn't afford to send it back to Tak either. I think Martin Pugh (I may be wrong - correct me if so) may have done it sometime sorta recently at the cost of thousands and so did Exfso, as we all know.

My stage of life atm that's an unaffordable exercise. So I'm keenly interested to hear how this turns out.

Does anyone know what the "magical instrument" is that Takahashi Japan uses to assist in recollimation?
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  #6  
Old 23-01-2018, 11:17 AM
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tempestwizz (Brian)
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Thanks for your words of support Les.

Waves may have missed the bit where I said the front element was loose when I received it from an earlier user.

He may have also missed it where I said that the retaining ring for the rear element was about a turn and a half loose also. Not a standard Tak feature, I expect.

I did not state before, but I noted that two of the six larger adjusting/retaining screws were without flat washers when I removed the. Another non-standard Tak feature, which indicates someone has had it apart before me.

So I can’t take all the credit for mucking it up.

Nothing appears broken, so it should be simply a matter of adjustment to restore it to its former glory - now that the rear element is again secured.

The info provided by Les, and the tear-down shows that the inner set of adjusting screws is for the whole assembly, but more importantly is the only adjustment that affects the two rearmost elements. It is not a critical adjustment for spacing, only for angular orientation of the assembly.

The critical adjustments are for the front element only. Spacing for CA, and angular orientation for airy disc.

Maybe I did not have much of an idea when I started, but I think I have done alright so far armed only with what I have.
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  #7  
Old 23-01-2018, 05:19 PM
Kunama
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Keep at it Brian,
so long as you don't scratch anything or leave contamination inside when you close it up, the worst that can happen is to box it up and take a ski trip to Tokyo. Be aware of any thing that may grow fungus once closed.

I was under the impression that the second set of push-pulls adjusted the centre element, apparently not.

Are there any adjustment screws for actual centering of the elements or is that set with spacers?

Be aware that over tightening the retaining rings can induce astigmatism.

Take lots of photos...

Cheers,
Matt
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  #8  
Old 23-01-2018, 10:08 PM
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tempestwizz (Brian)
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Thanks Matt. The two rear elements are fixed into the main assembly. There is no adjustment for centreing nor for spacing or angular adjustment between them. Only adjustment may be rotation of the elements, but I have not seen any markings to indicate a rotational reference.

As anticipated, I have spent my time slowly changing the separation between the front elementand the two fixed elements while maintaining angular alignment for airy disc pattern and checking visually.
I am using an artificial Star I made from some fibre optic cable and a white LED. My ccd camera does not show clearly the airy Discs pattern right at the focus point. I need to use an eyepiece and view by eye. I use a Tak 3.6mm eyepiece which gives about 250 times magnification.
The adjustments are a tedious process. Less than 1/10 of a turn produces a huge affect on the airy disc pattern.
It seems adjustments to the front element have most visual affect on the airy disc pattern outside of focus, while the adjustments to the whole assembly have a most visual affect on the airy disc viewed inside of focus.

I think I am getting close to setting it right. I will continue tomorrow.
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  #9  
Old 24-01-2018, 02:50 PM
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Exfso (Peter)
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I reckon you have a huge set of "kahoonas" doing this, most interested in the outcome. I believe the Tak techs use all sorts of optical wizardry and bits and pieces to collimate these scopes.
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  #10  
Old 24-01-2018, 03:42 PM
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Logieberra (Logan)
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Watching with interest...
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  #11  
Old 24-01-2018, 08:06 PM
Kunama
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Quote:
Originally Posted by Logieberra View Post
Watching with interest...
Likewise !!!

Lets face it, there is no magic to it, it is just three pieces of glass that apparently are kept centred by the cell and perimeter spacers. Given that Brian tells us the the 2nd and 3rd elements are in fact in fixed positions then it is just a matter of time before Brian hits the sweet spot for the front element.

Keep going....
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  #12  
Old 24-01-2018, 08:44 PM
thebonz (John)
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Toa

Keep going if you are making progress
John
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  #13  
Old 24-01-2018, 08:52 PM
thebonz (John)
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toa qsembly

reading your previous posts regarding Loctite on a lens cell ???
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  #14  
Old 24-01-2018, 09:48 PM
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tempestwizz (Brian)
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Given that somehow the retaining ring had come loose before, I thought just a small drop of Loctite on the outside thread should prevent it from occurring again. I’m not the sort of bloke that carries nail polish, maybe that would have been a better choice.

After more time spent today, I think I’m close. Plan to look at some real stars through it tonight. For practical reasons my artificial Star is located outside of my workshop, and I get localised turbulence because of the heat from the sunshine. Makes it harder to see the image at the 500 times magnification I’m using in the image train.
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