TAL 100 RS - collimation on a refractor

[moriniboy]

My TAL 100RS uses a mirror in the diagonal to overcome any collimation errors.

The only problem is I want to get a 1.25" dielectric diagonal and I can't find one which you can collimate.

This is how far out the collimation is, am I being paranoid or does it need to be spot on.

Ultimately I'm going PST solar stage 2 with this scope, not sure how good collimation needs to be for solar work?

Thanks Nigel

[AndyH]

So, if I'm reading this right, it's the focuser that's out of alignment?

Cheers,

Andy.

[moriniboy]

Yes thats right Andy

I've worked out a mod to the focuser to allow collimation but If its currently close to optimal then I may just leave it alone.

When I took the photo it had a collimated laser inserted direct into the focuser, it did not have a diagonal fitted.

[John]

Collimatable diagonals are quite rare, especially in the 1.25" size. Some of the old TAL ones did have push-pull collimation screws under their back plates though, if you can find one of those.

The alternative is shimming the edges of the focuser, when it is attached to the tube, to tilt it to get that red dot in the centre of the objective.

I've had quite satisfactory views with refractors that are a bit out as yours is but the knowledge that things could be a bit better eats away at you

Once the dot is central, ie: the focuser is square with the optical axis, you can check the tilt of the objective using a cheshire. This is the 2nd stage of refractor collimation.

[AndyH]

Tal diagonals have always been and still are collimatable. Tres handy feature.

The 2" are also, but I doubt if many, if any, have made their way out of Russia.

[AndyH]

I think, I'd try and get the dot, even a bit more central with some sort of shimming. I'm pretty sure the views shouldn't be comprimised, but, like John, it would bug me, a wee bit.

[nightfisher]

Just a thought, but if the laser is out just a small amount, then over the length of the tube it would be out further if the views through the scope are good, then i would leave well alone, or stick with the Tal diagonal as this is ajustable and probably as good as a dialectric

[moriniboy]

Good point re the laser but i've collimated that as well

I'm very happy with the current views but when you find that somethings out you always wonder what if?

I'm on with the mod at the moment, currently using a 1mm washer to shim the focuser, will post some photos once completed.

[moriniboy]

Ok so I've finished shimming and its close enough for me.

Also tried with a 2" diagonal (non adjustable) as well as the original TAL 1.25" item and both are spot on.

Currently I'm out looking at the moon and my 17mm Hyperion is giving me the best views I have ever seen.

Well worth undertaking this mod in my opinion.

[AndyH]

Reeesult !!

I think I know what you've done, but if you get the chance to take a pic of how you shimmed it, it may make a nice reference to anyone else needing to do this?

Cheers,

Andy.

[Astro_Baby]

Andy, as the TAL expert round these parts, I am messing with my 100. i am planning on shimming the front lens as my own 100 is fractionally out using a chesire, the dot is around 1mm off true and as I suffer from telescope OCD its doing my head in.

I could corect this with the diagonal but the diagonals I have are also used with my Mak so I would rather get the scope perfect rather than correct via a diagonal.

I am assuming the small set screws around the lens are to centre the objective rather than to adjust tilt for collimation errors. Am I right ?

I am planning on resolving the collimation error, tiny as it is, using PTFE tape on the tube and ideall doing this under the lens element as the tube wall is quite thick there. Any suggestions as ro a better way to accheive this gratefully received.

[AndyH]

Hi Mel.

Happy Christmas!

Once the focuser has been checked for alignment(I use the laser dot method for this), then the lens cell can be shimmed if necessary to get it bang on too.

Pic shows 1 of the 3 lens cell to tube securing screws.

Yes, these screws simply attach the cell to the tube.

There are other screws found inside the slots(if I remember correctly). Those ones gently hold one of the lens elements in place in relation to the other lens.

It's something I never did to the 100RS I used to have, so can't give much more insight I'm afraid

Let us know how you get on. Will be of interest to me and others, I'm sure.

Cheers,

Andy.

[Astro_Baby]

Yup its the small set screws I was interested in. I imagine if they push against one lens only then youd need some kind of fancy gear to align them.

Looks like I will have to shim the focuser or the lens cell. Thanka for that Andy ......oh and merry christmas too

[Peter Drew]

On my 100 Tal I opened up a little more clearance on the holes that accept the focuser unit screws and placed some stainless steel washers under the screw heads, this enabled a small amount of adjustment to be made before tightening down. Not quite as positive a fit as the countersunk original but plenty good enough.

[TonyD]

Hi Mel.

Happy Christmas!

I use the laser dot method for this

Hi Andy,

Out of interest, what's the laser dot method?

Cheers

Tony

[AndyH]

Hi Andy,

Out of interest, what's the laser dot method?

Cheers

Tony

Similar to moriniboy above.....

With diagonal removed, insert the laser into the focuser(make sure it's collimated and true !!).

If I'm doing it for the first time, I aim the scope tube towards the floor and don't clamp the laser with the thumbscrew, just in case doing this pushes the laser body off centre. If it doesn't then I gently clamp it up.

Switch it on and see where the dot falls on the scopes front lens. I'm lucky enough to have a holographic laser that projects a series of dots like this,

so I don't need to put a mask over the front of the lens cell. If I had a single dot laser, I would.

Then, if the dot/dots are off centre, the focuser needs to be shifted till it's aligned to the tube and lens.

Hope Moriniboy doesn't this hijacking of his excellent thread.

Andy.

[andrew63]

Just been reading this thread, although i don't have a tal, quite enlightening - certainly better than the endless pixar animations which seem to be on a loop on TV over Christmas!

andrew

[TonyD]

Thanks for the very informative reply, Andy.

What laser do you use?

I have a Logitech mouse presenter tool with laser pointer. Could that be harnessed in any way?

- Tony

[AndyH]

...........What laser do you use?

I have a Logitech mouse presenter tool with laser pointer. Could that be harnessed in any way?

- Tony

This one here, http://stargazerslou...790343_3858.jpg

Basically a precisely machined alu body with a laser inside, held by 6 grub screws, so it can be easily collimated if necessary.

The company have sadly long gone, but I bought lots of bits n bobs off them, in the day. This laser is probably one of the best accessories I've ever bought though. Wasn't cheap at US$80 or so, but it's paid for itself what with all the use it's had.

The only other company(that I can think of) that makes holographic type lasers are Howie Glatter in the US.

As for the pointer you have, I don't really know. But at the least you'd have to mount it into a body that could fit into a focuser, collimate it etc. So it might be more trouble than buying one designed for the job?

Andy.

edit

[TonyD]

Cheers Andy.

'

I'll check out if anyone at the local astronomy club has anything when I join this month.

In the absence of finding anything suitable like you have, are there any alternative ingenious methods that have been devised to do this job, I wonder

- Tony

[AndyH]

If the laser is a pen shaped one, then in theory............get someone with a lathe to machine a hollowed out body, similar to the helix above. Add 3 sets of 2 grub screws, collimate it and there you have a simple laser dot pointer.

Will be very basic in what it can do, but it'll work for making sure focusers are aligned at least?

Andy.

[John]

I use a standard Antares laser collimator (itself well collimated !) to check that the optical axis of the focuser coincides with that of the objective lens, using the same method that Andy describes. I also use a shorty cheshire collimator to check the tilt of the primary as per this method:

http://www.spacealbe...r/collimate.htm

Most of the refractors I've owned, with the exception of the Vixen's, required some slight adjustments to square the focuser and / or the tilt of the objective lens. I tend to be a bit obsessive about this though, to be honest !

F/10 refractors are probably tolerant of a little mis-collimation.

[Astro_Baby]

Hmmmmm I am getting weird results from a cheshire which makes me suspect the cheshire, starting to wonder if the cheshire itself is part of the problem.

If Ii go by the cheshire then the focuser is about 15' out of true, since thats pretty unlikely And I am betting other strange results that make me wonder about the doublet assembly itself I am off to d some serious reading and/or off to consult an optical expert.

If collimation was out by as much as the cheshire is suggesting views would be awful and they are not, they are pretty sharp so Am curious as to why the cheshire is producing such odd results. Also need to borrow a laser and see what it thinks. Dont own one anymore since the last cheapie one broke down (2nd cheap and nasty laser)

[TonyD]

Hi Astro-Baby,

Just wanted to say a big THANK YOU for all the time you have spent on your reviews and relaying experiences and understanding issues with the TAL 100RS - you have put up here and your own site. You really helped swing it for me on my choice of scope. I am really looking forward to getting my hands on the one I have bought and start using it. I going to set off to the UK in January to pick up a TAL 100R with original GEM mount and wooden tripod, and, if I can get one sourced and sent out to the UK drop-off address in time, a new TAL 100RS OTA. I was really looking for just a mount and tripod, but the 100R package (complete with EPs etc) was just too tempting. And a bit of history :-)

Cheers

Tony

[AndyH]

Possible interest for those with adjustable Tal diagonals? -

Once you know your focuser is true and aligned, you can then use the very same system to align your diagonal.

If you take the back plate off the diagonal, you'll notice that the mirror is glued to a rectangular plate, which in turn is held with 4 sprung screws, to the diagonal body. Most folk will put a cap with a centre dot, or thin paper over the nosepiece, insert the laser and adjust the mirror 'til it's centred.

Now put the diagonal into the refractors focuser and see where the dot falls on the fracs lens. Many a time, I've thought I had the diagonal aligned using the previous method, only to be rather taken aback by just how off it actually is at this longer distance. So I'd recommend this method if at all poss. If you reckon the diagonal is going to get bumped about a bit over the course of time, it might not be a bad idea, putting some 'thread lock' liquid on the 4 sprung screws. That'll keep them in place, yet be easily removed if necessary.

Maybe everyone knows about this, but I thought I'd add it just in case.