Limerick Astronomy Club

Hi,
I got an email from Mark Cahill saying that he doesn't want the 12" scope any more, does anyone want it?, its a fine scope optically and would be a nice piece of kit to have around, I'd take it myself, but I have a bigger scope.

How big is it Dave?
It would just be a matter of storage.

It certainly is, this thing is about 5-6 feet tall, infact here are some pics of it with Harry at my house a few years back,

Frank

I might be worth your while borrowing it for a while and check out your local seeing conditions with a 12" before investing in a possible C14. My local light pollution is not bad where I am but the seeing is not great. I can see almost as much with my 8" as with the 11" (planets that is) most nights.

BTW, it comes with 2 Baader planetarium eyepieces.

I wouldn't mind having it tonight the way the weather is!

All you gotta do is say you want it and its yours.

Just giving the heads up again, Mark doesn't want this scope, we can talk more about it at the club meeting in 2 days.
Before I had a big scope, I would have walked over burning coals barefoot to get this scope, I had it for a number of years way back and I can tell you its a fine scope optically.

H Frank,
Its great that you now have this scope, we all know the bad state the mirror is now in, you can compare it to the images further up in this thread, it was not looked after. They were taken about 3 years ago and it was in pretty good shape back then.

I think you and I agree that this scope needs to be revamped, so here are a few things we need to consider,

1, the focuser is a 1.25" type, this really needs to be a 2" focuser.
2, can we get some Teflon for the base and make it as smooth as it was many years ago, and cut the existing bolt so it fits properly.
3, do you think we can make a serious attempt at converting this to a truss design?, this is a big job that we should only take on if we can do it properly (given the cost).
4, if we stay with the closed tube setup, we need to put on some wood preservative, it has endured very well over the years but it does need a coat or 2.
5, if we stay with a closed tube setup, then we need to make a door hatch near the primary mirror so can cover the mirror directly when it's not in use.
6, The primary mirror cell is not centred, we should try fix this, if its not possible then replace the cell (but only as a last resort)
7, We need to have a proper go at cleaning the mirror and seriously consider getting it recoated.

Its hard to believe that this scope was built in the mid 1980s and has hardly changed since.

So, what do you think ??

Well,
the scope could be brought back to 100% easily enough as it is.
The timber is still sound even after all the abuse it's gotten.
I very surprised how well it's held up!
All it really needs is a good cleaning and some preservative.

The most important thing I'm sure you'll agree is re-coating the mirror,
After that, re-collimation, some Teflon, a new bolt and we're done.

The mirror cell gives me cause for concern and if anything needs to be
re-built it may be this.

I also think a new focuser is a necessity as the one on it is now very
much outdated.


As for re-designing it and making a truss.
Right now It's very big and cumbersome and to be honest,
If I didn't have the Jeep and workshop I wouldn't have it in my possession.

It'd be a great project to undertake and the way I look at it is,
having a club scope that is portable is almost a necessity.

Here is a design I found recently;
(not that I'm saying this exact one but something along these lines..)



and in it's storage state;





http://pw2.netcom.com/~ahighe/12_5ultra.html

Apart from the Primary & Secondary.
I guess we'd need a new spider and focuser which wouldn't be a huge deal.
The Timber and aluminum I can get cheaply through the building contacts I have.
It's the mirror mount I would think we might run into expense.
Unless there is a way we can make a solid enough one out of timber?

What d you think?
Mad or what?

That is one very impressive looking truss Dob, but there is one thing that design is not taking into account, DEW !
The secondary will fog over and so will the primary given the pic above, the one thing the obsession has is a very big mirror box, this serves as a mini dew shield for the 20" mirror and works very well, but the secondary fogged over last weekend, it has a built in dew heater, so I must get that working.
This would not happen in an enclosed tube design.

We need to examine the mirror cell and give the mirror itself a good cleaning, and re collimation, how about I drop over during the week sometime and we both give the scope a serious maintenance doing over.

Not a bad idea.
Let's take stock first and take it from there.
This week is out coz I've work on.
Next week should be better.

No problem, let me know nearer to the time when you are free.