Collimation. Secondry Mirror Washers

[Crossway]

A year or so ago I read an excellent feature herein on the subject of collimation but unfortunately I cannot recall the authors name. 

One of the recommended tecniques he mentioned was  to insert a couple of washers made from milk bottle tops into the secondry mirror assembly, the purpose being to facillitate the mirror adjustment.

Perhaps and hopefully the SGL author will see  my post and reply to my question .... ...  what is the exact function of the washers and how does their inclusion facillitate  the adjustment.

Pete.

[itmo]

the function of teh milk bottle washers (or any slick plastic, i use icecream box top plastic) is to act as a "lubricant" and make the motion smoother. The idea is that in most secondary mirrors (skywatcher..) the collimation screws dig holes into the soft mirror holder aluminium. The result is taht when you touch the screws they will pop in to the holes they have dug and the mirror rotates. To fix this you add a metal washer and under it a milkbottle washer. Idea being that the rough surface of the metal washer and the holes dont interact. Instead you get a sticky and smooth motion. 

[itmo]

And note that there are youtube videos of this conversion being made. 

[ronl]

I think it's this one you are after http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

just download the collimation file

[Crossway]

Thank you for explaining this to me,,,,,a very practical idea.  I had noticed that the three adjusting screws on my scope had starrted to embed themselves into the mirror holder which, on the Astromaster , is plastic. So therefore worse than aluminium of the SW I should think. 

Pete

[Crossway]

Thanks Ron......will download pronto.  I had been trying to locate the article on "Search" but with no success although bound to be there somewhere.

Pete

[Moonshane]

Yes they act as described above. The main thing they allow is a little tweak at the end

[acey]

I adopted the milk-bottle washer trick a while back and posted about it:

http://stargazerslounge.com/topic/41454-cure-for-jumpy-secondary-syndrome/

As has been said, the idea is to avoid the jumpiness you can get when trying to adjust the secondary. The same little piece of milk carton I inserted back then is still doing the job 5 years on.

[Crossway]

Wouldn't you think that the scope manufacturers would include these washers as a standard because they must be aware of the wee problem and the ease with which it can be solved.........mmmm, .perhaps I have just hit on the reason there!!.  I have just completed the op. with great success .  Took about 5 minutes.

The Astromaster "Manual" has a mild caveat in the collimation section and that is not to loosen the centre bolt in the secondary assembly when collimating.  Fine, but  on  setting up the scope for its first outing I realized that it would not focus owing to the fact that the secondary mirror was well " out"  by a good half inch.  If I'd known about the washer trick I would have would have fixed it then.

Pete.