200P Secondary Adjustments

[lw24]

Hi all,

Checked the collimation of my 200P Dob earlier, and it seems a little off. I determined that the secondary mirror needed to be tilted, so I tried to adjust the three small screws which supposedly change the tilt of the secondary. For some reason unknown to me, these hex screws are extremely tight, and trying to turn any of them clockwise or anti-clockwise results in the spider vanes flexing, and the hex screw not budging.

Are these screws supposed to be this tight, or am I doing something wrong?

Clear Skies,

Luke

[littlebeagle]

I had the exact same issue, make sure the scope is horizontal and be careful they will come lose with a bit of persistence. One bit of advice I got was to loosen the central screw, but I had as much trouble with that.

[lw24]

Yeah, the central screw is also incredibly tight

[Gloris]

i've just spent about 3-4 hours getting my secondary mirror aligned....last time I collimated, the secondary seemed fine, just needed to adjust the primary...

just got my cheshire yesterday so gave it a go today....it certainly made collimating the primary alot easier, it's alot easier to make out the circles and get it all sorted out.

but before i could do that it took me a good 3-4 hours to do the secondary....in the end i just loosene it all off completely, then made gradual adjustments until it was spot on....i've ordered some "bobs knobs", so i'll have to go though the whole process again when i get them...and i've seen on some sites about putting a piece of teflon and a metal washer between the secondary holder and the secondary mirror (as i've already discovered that the indentations of the previous positions do make it difficult to adjust, as the screws want to just jump back into these holes....so next time i'll do that too).

mine are not nearly as tight as they used to be now though....

I guess collimation is just one of those things you have to practise and get used to doing it though.

[Jason D]

Hold the secondary mirror stalk (not the secondary mirror) with the one hand while loosening the centeral bolt with the other. This method will remove all pressure/stress from the spider vanes. If the 3 set screws are still tight after loosening the central bolt, use the same trick I described.

Jason

[Jason D]

and i've seen on some sites about putting a piece of teflon and a metal washer between the secondary holder and the secondary mirror (as i've already discovered that the indentations of the previous positions do make it difficult to adjust, as the screws want to just jump back into these holes.

What I have suggested to use few years ago are washers made from Milk plastic containers. They work better than a steal washer because their elasticity helps making fine secondary mirror adjustments with ease. Many have used the idea with great success. If you do not want to remove the secondary mirror to place the Milk container washers, you can make radial cuts. See attachments.

[Gloris]

cheers, that's not a bad idea at all...will give it a whirl when I get the bobs knobs.....but having jsut sorted the secondary, i don't plan on messing with it too much until i get them