refurbishing a tired tal-110mm

[sparkyjon]

A few weeks ago i happily bought my tal-1 off someone for £50 knowing the OTA was in a bit of a state , i only really wanted it for the pier..

i've been looking in to cleaning up and refurbishing the old tube, it's heavily scratched probably needs collimating and i'm struggling to focus it....

now i'm planning on sanding it down and respraying it with a nice new coat of white, i'm also going to clean the mirror (it really is dirty) and collimate..

i'm thinking about changing the focuser on it anyone done this? would any newtonian focuser do the job?

[Gweedo]

Don't know about the replacing the focuser, but Astro-Baby did an excellent tutorial on a strip down and re-build which should provide some guidance:

http://www.astro-baby.com/TAL%20Telescope%20Rebuild/TAL%20Telescope%20Restoration.htm

[Astro_Baby]

Yeah but I never finished it.......one of the headaches is the TAL focuser on mine was busted. I fitted a replacement but the replacement is a higher profile The old TAL 1 s used weird eyepieces where there field lens is almost at the bese of the eyepiece whereas modern EPs have the field lens quite some way up the EP barrel. Combined with the higher peofile focuser ( the standard TAL one will take the EP in quite close to the tube ) it means you cant focus without moving the mirror up the tube by about an inch.

That sound simple but on the TAL 1 it mean either upi have to machine the end of the tube...hopelessly expensive OR you have to come up with something terribly clever. I did come up with something terribly clever but its a lot of woek to get it together and other projects have gotten in the way.

I am planning on making the TAl a kind of steam pubk retro these days WHEN and IF I ever get time

[sparkyjon]

Would a replacement focuser work if i didnt use their EP as the ones i had aren't up to much anyway they are badly scratched.

[nameunknown]

Hi

I had real problems getting my old TAL Newt (first scope) to work well with any other EP's (bit of a pain when I shelled out on my first Plossl in the days before the www). As Astro_Baby says, it appears to need quite some mods to get the field lens of the EP's to be in the right place. If you replace the focuser you may still have to move the mirror forward (or the spider and the focusser further down the tube). Years later, I even tried to use it as a guide scope (STOP LAUGHING), but even with that it was a real problem getting focus with an adapted web-cam.

Still ... it gave me my first "WOW" view of a smoky yellow Saturn and rings, many... many years ago.

P

[Astro_Baby]

If its an older one with the old TaL EPs which arent 1.25 ....they are slightly oversized then a modern EP wont work, not enough focus in travel which will require the primary to be moved up the tube. If you add another focuser, unless i has very very low profile chances are the same problem occurs. Your choice of focusers is severely limited becaise the spiders fixing points are so darned close to the edge of the focuser. I adapted a skywatcher focuser for the job but it doesnt have enough in travel.

You can get the main mirror up the toob by putting some longer bolts on and longer springs bu I found i hoplessly wobbly and horrible.

my next idea is

to have some longer bolts but with shrouds like long spacers which will be araldited to the rear plate. At the end of the shorouds will be some washers and the springs will be sandwiched between the waster and the mirror cell. Some longer lock bolts will also be needed. Tis a real palava and i have had no time to play aboit with it. The other alternative is to dicth the existing mirror cell and replace it with something else but thats money money money.

[sparkyjon]

hmmm this is starting to sound like a lot of hassle and hair loss (bald already) i cant moan too much as i only bought it on the promise that the pier was all good , and it is , i think i might concentrate my efforts on adapting my EQ 3-2 mount to fit on the pier , need a quick release type fitting to take it on and off..

[sparkyjon]

Stripped my tal down to bare tube. As soon as i can i'll get a metal spray, sand it down and respray.. I've even managed to clean up the original EP and they aren't as bad as first thought.

Back to the focuser is seems i don't have one it just looks like an EP holder i thought it was a twist focus that was just stiff but its not. Its a 1997 model if that's any help.

[sparkyjon]

You can get the main mirror up the toob by putting some longer bolts on and longer springs bu I found i hoplessly wobbly and horrible.

my next idea is

to have some longer bolts but with shrouds like long spacers which will be araldited to the rear plate. At the end of the shorouds will be some washers and the springs will be sandwiched between the waster and the mirror cell. Some longer lock bolts will also be needed. Tis a real palava and i have had no time to play aboit with it. The other alternative is to dicth the existing mirror cell and replace it with something else but thats money money money.

there might be a simpler solution to this , is to just cut the tube down when stripped and redrill holes for the screws , it shouldn't be too much of a problem. i've ordered a cheap newt focuser and i'm going to try it out , if i need to move the primary up the shaft i think i'll just cut it down before i respray it and shorten the whole tube..

[AndyH]

I wouldn't cut the tube down, as it would make things rather complicated.

Don't know if you've taken the primary mirror cell off of the tube, but if you do, you'll notice that the seamless aluminium tube has had a millimeter or so, machined off it's interior, for a perfect slip fit of the mirror cell into the tube. So if you chop a bit off the tube, the cell will NOT fit into the tube.

You'd either need to get the tubes interior machined down or get the mirror cell's exterior O/D machined down. Far too much hassle and cost.

I'm intrigued as to what the focuser, that you got the scope with, looks like. Does it look anything like this early type, slip fit version. Pic taken from A_B's webpage..........

'97 is not that early of a scope, for it to be really weirdly different. Have you just got the shell of the focuser, I wonder, with all the bits stripped off? If you can upload any pics of it, that would be of great help.

If you had a working focuser and you needed more infocus to get eyepieces to focus correctly, then I'd recommend going down the longer spring and setscrew route. Cheap and it works, especially if the springs used are as strong as possible. If the springs are weak(ie:thin wire), then this fix isn't going to work terribly well, as the collimation will probably move too easily.

[sparkyjon]

hi andy i dont have anything like that above , there is no rack and pinion it's just like an EP holder

this is it:

[TonyD]

crickey! how would you focus with that then? Just pulling the ep shaft in and out and clamping it with the screw?

[sparkyjon]

thats the only way i could think of, i have now bought a second hand one off astrobuy and it's the same one as andy has posted above, it's strange as everything is the same i.d hole ,.fixing holes so i dont know whats going on with the original focuser , unless my memory is wrong and it was 1987 not 97 on the sticker maybe the scope is older than first thought , unfortunatley i removed it for respraying and now destroyed it..

[TonyD]

unfortunatley i removed it for respraying and now destroyed it..

Oooh, the OCD in me says "never do that!". At least, have a full photographic record of whatever the equipment was or looked like before you take on anything major.

Sometimes there is a date on the mirror cell or cell holder? You might find some info stamped somewhere on the beast.