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Tal 100RS Collimation Shock

Damo636

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Damo636

Damo636

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Hi Everyone. I have noticed lately that my Tal 100RS was not as sharp as i remember it when i first got it. I had been putting it down to bad observing conditions. Last night i set up the dob and the Tal to compare on Saturn. The Tal really struggled where as the reflector gave some lovely views at times. I knew something had to be wrong. On examination this morning i found the primary cell had some slight movement in it. One of the screws holding the cell in place was loose!! I tightened up the three screws holding the cell in place and hoped this would cure the problem. I followed a tutorial online on how to check collimation using a cheshire directly into the focuser without the diagonal. I have attached acouple of pics of the view through the cheshire. They are not great as i was holding a mobile phone to the peep hole in the cheshire but i think it shows the collimation is out. I know the primary is adjustable but very nervous at going about it in case i make it worse. Any advise on this would be greatly appreciated.

Damo

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John

John

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The scope does look out of collimation to me (as some of my refractors have been) although the star test might not show much - F/10 refractors are resonably tolerant of some mis-collimation although it's nice to think that they are capable of giving of their best rather than 90% of it.

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Damo636

Damo636

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The scope does look out of collimation to me (as some of my refractors have been) although the star test might not show much - F/10 refractors are resonably tolerant of some mis-collimation although it's nice to think that they are capable of giving of their best rather than 90% of it.[/quote

Did you find the collimation difficult of your refractor's difficult John? I have read the tutorial but terrified of making it worse! As you say though, it would be nice to have it performing to its full potential.

Damo

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John

John

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Did you find the collimation difficult of your refractor's difficult John? I have read the tutorial but terrified of making it worse! As you say though, it would be nice to have it performing to its full potential.

Damo

If you have a collimatable objective lens cell it's pretty easy - just adjust the push-pull screws until the 2 spots of light through the cheshire show as 1.

If you can't collimate the objective then it's more difficult - you can make some progress by shimming the focuser to tilt it a little and check that the objective lens cell is square to the top of the tube.

I thought the TAL 100's has collimatable objective lens cells but I don't think they use the simple push-pull approach :)

Maybe another owner of a TAL 100 could help here - I've not owned one for over 10 years now :eek:

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  • 8 months later...
Damo636

Damo636

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I never had the chance to sort it as shortly after this happened.. http://stargazerslounge.com/discussions-scopes-whole-setups/141556-tal-100rs-vs-die-cast-fire-rescue-truck.html

The replacement cell looked the same through the cheshire and i came to the conclusion that the fault was in the position of the 3 holes holding the cell. in place. One of them seemed to have been drilled slightly further up the tube and it was pulling the cell off square when tightened up. I removed the offending screw, tightened the other 2 up and covered the empty hole with a little bit of clear silicone to stop condensation getting in. It never looked perfect through the Cheshire but star tested perfectly to my eyes. The new owner was delighted with it and found it really sharp so i guess at f10 they are pretty forgiving of slight miscollimation.

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  • 3 years later...
Darkmatter

Darkmatter

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Thankfully it is collimatable John. It has 3 very small screws in addition to the 3 larger holding the cell in place. I'll give it a go later. Cheers.

Damo

Does anyone have any pictures available of where the small screws are ?

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Roy Challen

Roy Challen

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Does anyone have any pictures available of where the small screws are ?

Sorry I don't have pictures at the mo, I'm using the phone. The collimation screws are easy to find, remove the dew shield, you will see six screws, 3 small ones at the lens end of the cell, 3 larger ones at the tube end of the cell. The collimation screws are the small ones. Hope that helps

Roy

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philj

philj

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Hmmm, my memory of Tal rs are that they are fixed collimation. Well the one I played with was anyway, it was the plastic cell one.

There are 3 countersunk screws holding the plastic cell to the tube but there are 3 small grub screws protected by sealant which I havent messed with but I think they just centre the objective.

The Tal instructions, from what I remember, says you collimate using the collimatable diagonal. Now this to me is not really on cos the collimation will only be right if you use the same Tal diagonal. Use another diagonal or accessory and your out.

I found with the rs I played that the tube was distorted causing collimation issues, I collimated and redrilled the cell fixing screw holes. The collimation was spot on no matter what accessory you fitted.

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Roy Challen

Roy Challen

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Hmmm, my memory of Tal rs are that they are fixed collimation. Well the one I played with was anyway, it was the plastic cell one.

There are 3 countersunk screws holding the plastic cell to the tube but there are 3 small grub screws protected by sealant which I havent messed with but I think they just centre the objective.

The Tal instructions, from what I remember, says you collimate using the collimatable diagonal. Now this to me is not really on cos the collimation will only be right if you use the same Tal diagonal. Use another diagonal or accessory and your out.

I found with the rs I played that the tube was distorted causing collimation issues, I collimated and redrilled the cell fixing screw holes. The collimation was spot on no matter what accessory you fitted.

Hi Phil, just a quick question, what effect would adjusting the centre point of the objective have?

And plastic lens cell...? On a Tal?

Roy

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John

John

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I believe that you need to get the objective lens optical axis central to the tube and in line with the focuser optical axis. It's the first stage of refractor collimation. The 2nd stage is to tilt the objective, assuming that the facility to do this is built into the objective cell. The 1st stage can be checked with a collimated laser collimator - the laser beam should exit the objective lens more or less in the centre. The 2nd stage is checked with a cheshire eyepiece. If the tilt of the objective is off you will see two reflections from the cheshire. When properly adjusted they should show as a single relfection.

An F/10 refractor is tolerant of a little miss-collimation though, I reckon.

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philj

philj

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:-)

Ive always thought I should have one but after messing about with 2, pimping, repairing and using, Ive never got round to it. I would sooner stick with my f15 I reckon

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