Which screw is which please? Newtonian Mirror screws

[mrphildog]

Hi,

This is my new Skywatcher Explorer 150P. The instructions describe a few different screw layouts but not this one. Could anyone help me and tell me which is the locking screw and which is the adjusting screw?

Much appreciated.

Thanks

Phil

[Peter Drew]

The large knob is the adjusting knob, the other is the locking knob.

[toilandtrouble123]

What do they do? I'm getting a 150 soon, my first reflector...should be interesting..

[mrphildog]

The large knob is the adjusting knob, the other is the locking knob.

Thanks very much. By "large" I take it you mean the fat one is the adjusting knob as opposed to the long skinny one? :-)

Cheers

[mrphildog]

What do they do? I'm getting a 150 soon, my first reflector...should be interesting..

Hi, they are for adjusting the primary mirror to line it up with the secondary mirror i.e. "collimating" the telescope.

[toilandtrouble123]

ohhh ok.... lol, refractors are so much less technical. When it comes to first light with mine, be prepared to be bombarded to questions and cries for help haha!! x

[MorningMajor]

Thanks very much. By "large" I take it you mean the fat one is the adjusting knob as opposed to the long skinny one? :-)

he does

[mrphildog]

he does

Thanks. :-)

[WaveSoarer]

My 200p looks the same. The thin ones are the "locking" screws, though they're pretty redundant really. The chunky ones are spring loaded and so they maintain tension. When I first collimated the telescope one of these was really tight at the end of its travel. They should turn reasonably easily.

[mrphildog]

My 200p looks the same. The thin ones are the "locking" screws, though they're pretty redundant really. The chunky ones are spring loaded and so they maintain tension. When I first collimated the telescope one of these was really tight at the end of its travel. They should turn reasonably easily.

Thanks. If it was really tight at the end of its travel what did you do in order to collimating it? I presume you had to loosen it and then adjust the other two?

[WaveSoarer]

I just loosened it by using a bit more force than ideal. It was just screwed in too far. In principle you only need to adjust two of the screws anyway to achieve good collimation. Astrobaby's guide will help with this but you'll need a Cheshire or a collycap. I suggest you get out and use your scope before worrying about collimation. It's all too easy to get fixated by it and your scope is unlikely to be grossly out.

[mrphildog]

I just loosened it by using a bit more force than ideal. It was just screwed in too far. In principle you only need to adjust two of the screws anyway to achieve good collimation. Astrobaby's guide will help with this but you'll need a Cheshire or a collycap. I suggest you get out and use your scope before worrying about collimation. It's all too easy to get fixated by it and your scope is unlikely to be grossly out.

Ah, right I see.

I've got a Cheshire on order. I used the scope for the first time last night and I did a star test, as far as I can tell the rings were concentric so if it is out of collimation it's not by much at all. Also, the view of Jupiter I got was excellent so it seems to be working pretty well. :-)

Thanks for the help.

[WaveSoarer]

That's good mrphildog. I expect that your scope is in good alignment already and the Cheshire will help you tweak it spot on. Incidentally, you may not be able to see the primary mirror clips with the Cheshire as you wont be able to rack the focuser in close enough. I certainly found this. You only need to see the edges of the primary (as indicated by the clips) if you're using a colly cap as it lacks the cross-hair of the Cheshire. To tweak the tilt of the secondary with a Cheshire you just need to line up the cross-hairs with the central mark (polo mint) on the primary. Just use very tiny tweaks on the alignment screws (loosen one a tiny bit and tighten another, to compensate, a tiny bit) and you should be ok.

[barkis]

I'm a bit baffled by that image. Are we looking at the mirror cell rear end?

Those seem like lateral adjustments to me.

[WaveSoarer]

It is the bottom of the mirror cell and the chunky screws (with springs) tilt the primary.

[mrphildog]

I'm a bit baffled by that image. Are we looking at the mirror cell rear end?

Those seem like lateral adjustments to me.

That's the back of the mirror yes. There are three pairs of screws like that. In the image the scope is in its mount pointing upwards. The angle of the pic and being a closeup may make it hard to envisage the bigger picture perhaps.