tweaks for secondary mirror set screws ?

[jonstarrysky]

3 small screws are used to adjust the tilt of the secondary mirror of a Newt. When they are loose you can also rotate the secondary. Basically it is a fiddly and tricky business.

On cloudynights, there have been some ideas to improve this somewhat, notably by adding washers on top of the plate that these 3 screw push against.

Telescope Reviews: Squirrely secondary mirror adjustments

Some ppl use metal washers, or even a washer fashioned from a milk container, which apparently works wonders. It increases the ease by which the mirror can be rotated, and tilt adjusted. It also protects the secondary mirror holder as the 3 screws will wear out indentations where they press against.

Has anyone on this forum experimented ???

[DanDare]

I have a homemade spider/secondary holder with the usual 3 alignment screws which I hope to fit in the next month or two. Not ever having used/owned a newt before I hadn't realised that this 'problem' existed. I'll be watching this with interest.

Is this something you have been experiencing johnstarrysky, were you going to have a go at any of the suggested 'fixes'?

Roy

[jonstarrysky]

Roy

I may have a go at the Milk carton fix. This comes from a guy called Jason B who apprears to be an authority on several astro kit issues and collimation.

I am new. But my limited experiences of adjusting the secondary are consistent with that thread, it can be somewhat fiddly and awkward. My own secondary is adjusted correctly for the focusser axis i.e. it points light precisely towards the primary centre spot. But there is a rotation error. With the secondary adjustment you have the physical position of the mirror in all 3 dimentions PLUS its rotation PLUS the tilt of the same mirror in all directions. So lots to adjust if you want it spot on and the three screws set-up is not ideal (but works).

[Astro_Baby]

Secondary rotation is quite common and the source of TONS of frustration for novices and the experienced alike.

Usually I can recollimate from scratch in under about 20 mins BUT recently I wanted to fiddle with something that meant taking the secondary out and it took me HOURS because rotation error kept reappearing plus I was having an off day I think.

Collimation is all about re-iteration. Going back over each step;

Align secondary to focuser

Aligh secondary to primary

recheck alignment to focuser - adjust if necessary

Realign secondary to primary if necessary

Ad infinitum until both are ok.

Now align primary to secondary

recheck secondary to primary alignment - adjust if necessary

Recheck primary to secondary

And again ad-infinitum until its all perfect

Its often slow, often painful and sometimes amazingly aggravating but I chill, have some tea between stages, be calm and patient and reflect (pardon the pun) on the universe, the beauty of Newtonian design and whatever else may make me calm and wonderous and receptive.

Remember its only the secondary which has the potential to seriously damage your mental health Thankfully you dont often need to radically mess with the secondary unless like me you are totally mad to start with :)

Now I shall have to dismantle again to try the plastic washer and see if its cool. I like the idea of a spring loaded third adjuster as well.

[jonstarrysky]

Thanks Astrobaby. I actually have a print out from a previous collimation posting of yours siting on my desk at home, which I use for reference. This is an interesting post too, delving into secondary rotation etc:

Telescope Reviews: Useful info about secondary mirror alignment

My secondary is now on that desk too (in a sealed bag). And I have some steel washers that will be glued to the secondary holder. And some milk containers. And bobs knobs. We'll see what I can do with all that.....

Pls feedback on plastic washer experiences !!

[MikeD]

I cut out and used the core of a CD and it worked very well for me.

It means I can now square it all up loosely and still rotate the secondary without having to loosen the three screws again and lose square. When you are happy just nip the screws a tad to lock it all tight.

It's been in there around two years and is still in one piece.

Mike.

[DanDare]

As already mentioned I won't be ready to fit the spider for a while but will try the milk carton fix when I do. I haven't looked at Astro_Baby's primer on collimation yet, but it I think its going to be required reading for when I get the 'scope finished.