Collimation tip - bottle washers

[Moonshane]

I rarely collimate the secondary on my 6" f11 Newtonian as it's always generally close enough. However, I had a spare few minutes yesterday and decided to do so. When I first bought the scope I did a few mods including the secondary

I added a stainless washer which had previously worked well but this time I found my efforts to get a spot on collimation slightly frustrated. I had always meant to try the often recommended 'plastic milk bottle washer' mod and thought I'd try this. Using a standard four pint plastic milk bottle, I cut two circles of the appropriate size and put a hole in the middle. These were then added in place of the washer and I have to say work superbly well, giving much better fine tuning to the secondary tilt adjustment which stays exactly where you put it.

I'll be doing this for my other scopes (in fact I have done my 12" this morning and will do the 16" next time out. I'd recommend you do this mod yourself as it really does make the secondary tilt adjustment a lot easier.

I think our member JasonD came up with this originally and there's more info and a JasonD diagram in this CN thread http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5854490/Main/5853903

http://www.cloudynights.com/ubbthreads/download.php?Number=5853948

[stargazerslivingroom]

That's a great post for me...Thanks. I'm about to embark on this mod and have been trying to source the teflon washer used on another forum. I'll take your advice and use a milk carton.

Steve

[Moonshane]

I have used Teflon previously and it worked well but milk bottles are free and 're-use / recycle!'. I also use little circles from the tops to make green / red torch lenses (and for mixing small volumes of epoxy glue).

[stargazerslivingroom]

This is very interesting, Shane. The mod I was planning uses a ss washer (2mm thick) with three 1mm deep holes drilled to accept the ends of the collimation screws. The teflon washer comes AFTER this and sits next to the secondary. Your method does away with the ss washer but still achieves the same...preventing dimples in the base of the secondary causing bumpy adjustments.

Steve

[Moonshane]

Absolutely Steve. even if you do eventually get dimples, you can just turn the washer although the flexibility of the plastic washers means this is unlikely to be required. it's not my method BTW, it's Jason's :0)

[Jason D]

I think our member JasonD came up with this originally and there's more info and a JasonD diagram in this CN thread http://www.cloudynig...90/Main/5853903

http://www.cloudynig...?Number=5853948

Hello Shane,

I am glad you liked the milk-bottle idea (or milk-jug as we call it in the USA).

Absolutely Steve. even if you do eventually get dimples, you can just turn the washer although the flexibility of the plastic washers means this is unlikely to be required. it's not my method BTW, it's Jason's :0)

The screws will indeed cause dimples on the washer but that has no negative consequences since the washers are not glued/attached to anything. The secondary mirror stalk is still free to rotate underneath.

The most useful feature of the milk-jug washers is elasticity. Metallic washers do not have elasticity nor do Teflon washers. Elasticity will allow you to fine tune the secondary mirror adjustment by tightening one set screw without the need to loosen the other two.

Jason

[umadog]

I too have tried this mod and it works very nicely.

[Qualia]

Not being a previous owner of a reflecting telescope, I did wonder what that little disk of water plastic was and after collimating the secondary for the first time thought to myself what geniuses were the manufacturers. How tight everything remains, tilt and tweaks rock steady at all time. After much travel with my own Moonshane, often crossing rather unforgiving terrain, camping out for days on end (will include a post of my latest adventures with the Moonshane) there's no fear of collimating the entire scope both primary and secondary in the day or in the dark. I had no idea that this effective addition was a homemade mod! Hats off to Jason for coming up with the idea and thank you to Shane for sorting me out one hell of a beauty

[Peter Drew]

Whilst I think that the principle of this mod is so important that it beggars belief that manufacturers don't incorporate it as standard, I have always been cautious about using a deformable medium for the discs that are in direct contact with the adjusting screws. I would have thought that over time the compressible nature of such material might allow the collimation to wander, the experiences reported seem to suggest that this concern is unfounded.

[Notty]

Sorry I know this is an old thread, but having already found dimples in my 2nd'ry mirror backplate I am keen to incorporate this great sounding mod, but to be clear,  we talking about cutting discs from a standard plastic 4-pint milk carton as sold in the UK? 

Love to hear from anyone who has done it, thanks.

[Moonshane]

yes you are quite right. if necessary use two as some are quite thin.

[Notty]

Cool, sounds good, thanks.  Now to drink a lot of milk....