Collimation Headache

[Muc]

I have tried to tweak collimation on my 10" skywatcher classic dob. I believe I have made a mess of it which is no surprise really. I was trying to adjust secondary. Haven't touched primary. Views were ok originally but just wanted to learn to tweak as it has been brought to dark site a number of times in the car. 

One thing in particular has thrown me. Is the Philips head screw in the centre of the secondary mount a locking screw or an adjustment screw? All it was doing was moving the whole mount. I was working off a guide that had suggested that clockwise and anti clockwise movement were going to adjust the position along the axis of the scope. 

 

 

[Muc]

Also I think I accidentally touched the front of the secondary at one spot, the blue ish smudge 😬

[wimvb]

If you look at the reflection in the secondary, you'll notice that it needs tilting until the whole primary is visible. Also, you need some tools, like a collimation cap, to get a more precise view. With just a camera pointing into the focuser tube, you can't really tell how well everything is aligned.

The central screw on the secondary assembly is for moving the secondary up or down the tube. Be careful when adjusting it, or the secondary may come loose and fall down on the primary. Keep the scope horizontal when you collimate

[Muc]

10 minutes ago, wimvb said:

If you look at the reflection in the secondary, you'll notice that it needs tilting until the whole primary is visible. 

The central screw on the secondary assembly is for moving the secondary up or down the tube. 

Ok gotcha, and the tilting that needs to be done is performed using only the three  small hex bolts, is that correct?

I have a simple collimation cap and a chesire type eyepiece also 

[Muc]

Got to a better place with it, amazing what taking a break does !

[Enceladus Dan]

The Cheshire piece is all you need, keeps you eye at the centre and helps alignment. I've only done it once and found this page a good source of info. 

https://skyandtelescope.org/astronomy-resources/how-to-align-your-newtonian-reflector-telescope/

I found drawing the focuser out to reduce the space around the secondary made it easier to gauge it was central to the focuser tube. This pic has the 3 steps summed up in 1 image. 

Danny

Looks like you cracked it while I was typing. Well done. 

Edited March 18, 2023 by Enceladus Dan

[wimvb]

Much better, but not quite there yet. The secondary is not centered under the cheshire yet. In fact it almost looks like the secondary won't clear the cheshire. To get good alignment it's easier/necessary if you can see the edges of the secondary. The diagrams that @Enceladus Dan posted will help.

[Spile]

This explains the relationship between the three outer bolts and the central screw and how they affect the secondary mirror https://astro.catshill.com/collimation-guide/

[Muc]

18 hours ago, wimvb said:

Much better, but not quite there yet. The secondary is not centered under the cheshire yet. In fact it almost looks like the secondary won't clear the cheshire. To get good alignment it's easier/necessary if you can see the edges of the secondary. The diagrams that @Enceladus Dan posted will help.

Yeah I can see that the secondary is not centered correctly with the focus tube. I've taken a break from it for now and will return when I've a quiet day so I can be as relaxed as possible when tackling it. 

 

15 hours ago, Spile said:

This explains the relationship between the three outer bolts and the central screw and how they affect the secondary mirror https://astro.catshill.com/collimation-guide/

Wow thats exactly what I was looking for, many thanks! I'm reading it slowly here and I like how they have gone into the details.

Thankfully I got to use it last night with it's current setup. First proper clear moonless night in a long time. So got to see Markarian's Chain and other Spring galaxies for the first time. Feeling very thankful

[Spile]

You are welcome and pleased that you found it of use. I wrote it because none of the existing guides were quite right for me. As I acknowledge I am indebted to Jason and Vic who put me on the right path.