New Scope

[RobertM]

As some of you may know I've had an Altair Astro 10" RC for a year or two.  Trouble is I've found the focal ratio too long for my skies and the image scale too small for the seeing here in Orpington.  Well I sold that a week or so ago and have now replaced it with an Orion Optics 12" f/4 Newtonian; that will give me a nice fast 1200mm focal length and a bit more flexibility - I can use it on planets as well (hopefully).  It just about fits in the observatory, there's about 8" to spare on one side and no room to walk around any more (I've bumped my head a few times).

It seems that all newtonians have collimation issues !  This one had a rotated secondary that was set too near the mirror, consequently the collimation screws were all near their limits and crooked, tilting the secondary over to one side.  Strangely the primary seems to be spot on so at least that's a good thing.

You might even see some planetary/moon images from me sometime - yet another new adventure !

Robert
P.S. We've had clear skies since I picked it up so don't blame me

[Carole]

That is a big one Robert.  I sold my 8" SW 200PDS because I found it too big as I like to swap my scopes around depending on the target and I was finding the other scopes were not getting a look in as I had no-where to put it once off the pier.  I now have a much smaller 150P which is much easier to handle. 

Sounds like your secondary was completely messed up was it new or 2nd hand? 

I checked my Newtonian when I got it and found one of the spider veins was about 7mm shorter than all the others and it was bolted so tight I had to use pliers to free to nut, goodness knows what it's previous owner was doing.

Carole

[RobertM]

It was second hand Carole, there wasn't much money left in my secret slush fund.  The tube is quite short but about 15" in diameter which makes it awkward to handle especially with nearly all the weight at one end !

The spider on this scope is centred across the tube as close as I can measure it, just as well as like yours it would need mole grips to loosen the screws; it needed a complete reset but doesn't look too far out now.  I'm hoping just a tweak against a star is all it needs but fast Newtonians can be very fickle.

Robert

[Carole]

So is it a bit like Mark's Bananascope then i.e. with a more hyperbolic mirror, otherwise I can't get my head around how it could be shorter? 

Carole

[RobertM]

By short I mean just under four feet.

[Carole]

Lol

[RobertM]

Well a badly squeaky main mirror cell so after investigating...

The cell is balanced in a 9 point cell but each point touching the mirror is the end of a 6mm (guestimate) nylon screw, not especially good but the mirror is very thick so it probably won't affect the figure much I hope.  The mirror is glued to the 9 points via dabs of silicone sealant (anti mould I hope!), held in place with three clips and then taped around the outside with nylon reinforced packing tape.  In theory this is a good method since it allows the mirror to expand but not move too much IF there's no slack... sigh !  I've applied a fix that should work - more silicone sealant  under the three dolly's the mirror is sitting on and between the mirror and it's clips.  I think that should do, should find out tomorrow when it has set.

Re-doing the secondary from scratch tomorrow, fatal floor in my previous attempt - didn't start from basics !

Robert

[Fay]

You are a trier Robert

[MarkS]

How does a main mirror cell squeak?

The rest of your graphic description doesn't sound all that flattering.
It sounds like something a DIYer has built from scratch 

Good luck!

Mark

[The Thing]

I've been reading peoples blogs of what they had to do when their newt arrived to get it up to scratch, not encouraging! It's made me rethink my next scope purchase. Good luck Robert!

[Carole]

I've been reading peoples blogs of what they had to do when their newt arrived to get it up to scratch, not encouraging!

Oh dear, doesn't bode well for me, I have no technical skills except to collimate.  Mine is already flocked and I won't be taking it apart.  It either works or it doesn't, luckily I didn't pay much for it.

By the way the seller insisted on including the laser collimator as part of the bundle, and I prefer using a Cheshire, so I am planning on selling the laser collimator if any-one is interested.

Carole

[RobertM]

Squeak and main mirror movement sorted, now on to the secondary !

The spider was central but unfortunately the spider holder wasn't square to the tube - adjustment using the collimator screws puts it off square !  The collimating screws shouldn't be needed on a Newtonian other than for micro adjustment.  Next job is repointing and repositioning the secondary spider assembly.  I also had to slightly adjust the angle of the secondary as it wasn't 45.

[Fay]

could have been worse, wonder what would have  happened if I had bought it!!!!!!!

[RobertM]

could have been worse, wonder what would have  happened if I had bought it!!!!!!!

[RobertM]

Bah Humbug !!!

Nothing sits centrally in the focuser drawer tube, no wonder it was difficult to collimate.  I managed to get the set screws to hold a 2" extension at the right angle so I've collimated it with that.  It doesn't look too far out and isn't (fingers crossed).

New focuser on the cards though

Yes I think it's worth the hassle.

Duncan, it's not like you to give up like that !

Robert