Secondary mirror shock!

[Adz]

Hey all,

Well I have having a bit of a nightmare collimating lately. I have been following the guides and I have done it reasonably well before. But getting my secondary mirror to point to the middle of the primary is proving a nightmare.

I cannot fully understand the 3 adjustment screws and the central screw. The central screw doesn't even want to move at all and I don't want to force it because of bending the spider vanes (which might I add are a much stronger word than RUBBISH).

Now this evening wandering into despair I noticed that my secondary mirror holder isn't looking healthy at all. In face, it is at an alarming angle when shouldn't it be parallel with the end cover of the scope?

Help me sorry,

Adam

[sixela]

The spider vanes are just fine, but it looks like they need to be tensioned more (it's useful to insert a washer between the nut and the tube; if taut enough, the spider vanes should sing when plucked).

The central bolt and tilt bolt arrangement is a push-pull arrangement. To rotate the secondary, you loosen the central bolt, rotate the secondary, and tighten it again.

To adjust the secondary towards the front of the scope, you loosen the three tilt bolts and tighten the central bolt (be sure to hold the secondary's side to prevent it from rotating).

To adjust the secondary towards the primary, you loosen the central bolt (careful not to unscrew it completely, and make sure the tube is horizontal and that you can catch the secondary should it come loose completely!) and then tighten the three tilt bolts.

To adjust secondary tilt, leave the central bolt alone and unscrew one tilt bolt and tighten the two others or screw one bolt and loosen the two others. Finish by screwing in the last small adjustments to ensure some system tension.

[Adz]

Okay maybe I should have posted it elsewhere?

[rowan46]

this explains collimation better than I ever could Astro Babys Guide to Collimation or this video Collimating a Newtonian

[John]

Your secondary holder and vanes look just the same as all the brands of newtonians I have used. The vanes have to be thin to avoid adding unwanted diffraction to your images and reducing contrast. Have a look at Astro Baby's guide and see how it relates to your situation. You should not need to force anything to make adjustments. I suspect you have got some twist in the vanes running away from the camera in your photo which will need to be rectified - the top of the secondary holder should be pretty much parallel with the top of the tube.

[NGC 1502]

Looks like the vanes are bent. I see you are in Cambridgeshire. If you wanted,

you could bring your scope to me in SE Essex, and I will do my best to sort it.

Would be best Sat or Sun PM. It's a 2 hr drive from Cambridgeshire to SE Essex.

If this is any good to you, please send a PM.

Best regards, Ed.

[Lurker]

Looks like the vanes are bent. I see you are in Cambridgeshire. If you wanted,

you could bring your scope to me in SE Essex, and I will do my best to sort it.

Would be best Sat or Sun PM. It's a 2 hr drive from Cambridgeshire to SE Essex.

If this is any good to you, please send a PM.

Best regards, Ed.

That's very very very kind of you helping a fellow SGL user.

Thumbs up

[Adz]

Looks like the vanes are bent. I see you are in Cambridgeshire. If you wanted,

you could bring your scope to me in SE Essex, and I will do my best to sort it.

Would be best Sat or Sun PM. It's a 2 hr drive from Cambridgeshire to SE Essex.

If this is any good to you, please send a PM.

Best regards, Ed.

Thanks for the kind offer Ed. I actually have to drive back up to University this weekend and wont be back for a while Anyone have any tips for self bending them back properly?

Many thanks,

Adam

[NGC 1502]

Hi Adam. Don't know if you are a DIY sort with at least some basic tools, but if you

are, here is what I'd do.

I would remove the whole spider assembly, being very careful not to damage the

secondary mirror surface. Work with the tube horizontaly, so if you drop anything,

it wont hit the primary mirror.

With the spider out, and unsuported by the tube, it will be quite flexible. You may

be able to straighten it out with hand pressure, but go carefully. While the spider

is out, have a try at loosening the centre screw that you couldn't shift. With the

spider in your hand, you can get a much better hold on it than when it's in the tube.

Hold the centre hub firmly as you unscrew, being careful not to hold the secondary

mirror.

I wouldn't worry too much if you cannot straighten the spider perfectly, as minor

bends will be taken care of when you replace the spider and collimate using Astro

Babys well known guide.

Please go carefully, and good luck, Ed.

[Astro_Baby]

To loosen the centre screw you have to take some pressure off by loosening the three small screws around it.

The small screws adjust the tilt of the secondary, the large central screw adjusts how farup or down the tube the secondary sits.

Most good scopes have very thin spider vanes, they arent designed to take a lot of force but to be as possible.

With some tools you could remove the spider and then remove the vanes from the secondary holder and try and flatten them out a bit. Be super careful with the secondary.

I do fear though that you may easily make matters worse.

[Adz]

Goddam it I just wrote a detailed really happy reply to you all and then pressed a wrong button and lost it all!

To clear up, thank you so much for the guides and help I had a great go at it today and it looks perfect now just need to try my newly collimated scope out

Astro baby your guide was the Bible!

Oh and there is a little bit of give in my laser collimator at the focuser. So much so that it can cause the red dot to move all around the circle in the primary...?

Many many many thanks,

Adam

[Astro_Baby]

No problemo....glad its sorted

[sixela]

Oh and there is a little bit of give in my laser collimator at the focuser.

To minimise this, press the laser collimator against the shoulder of the focuser draw tube while fastening it; it's a registration with smaller tolerances (they have to make the barrel slightly smaller than all focusers for it to be inserted so there's always some wiggle room, but both the focuser draw tube's end and tool shoulder are nicely square to the focuser axis resp. tool axis and you can make them parallel uite precisely).

If it still doesn't register the same way all of the time, the barrel is probably much too narrow and you can usually fix that with two rings of aluminium tape on the barrel to thicken it until it can still just be inserted.

Don't forget to also rotate the tool 60° and retighten and see if the spot scribes a circle (which means it's miscollimated itself).