Newbie collimation help

[ThomasBR]

Hi, I need some help with collimation.

The waether service "promise" nice weather fro my area the comming weekeand so I thought I'd try to collimate my newton to get it in good shape for the weekend. I have read several tutorials on the net and it seemed doable. I have a chesire to aid me and the scope is a SW 200p f5 newtonian.

So in the first step I tried to center the secondary under to focuser and I used a white sheet of paper to block the primary to get red of all the reflections. The secondary was off to one side, I adjusted the spider vanes and got it centred. The secondary was also off towards the primary. According to the tutorials that can be adjusted by turning the central skrew. When I did that the secondary turned/twisted instead of moving. After being flustered abut the egg shape of the secondary I managed to get it back to looking like a circle. But, I cannot move it away from the primary. I think that maybe the secondary should be offset on a f5 system? and is that why it is closer to the primary? Could I turn any other skrew to move it away from the primary?

Not being able to move it I adjusted the tilt so that the paper-ring on the primary was in the center of crosshairs of the chesire. After that I adjusted the primary to get the reflection of the chesire black spot in the center of the paper-ring. Is that the right procedure? I have attached a picture through the chesire, does it look acceptable or am I way off?

Thanks for any comments and suggestions!

Thomas

[Dr_Who_46]

Im a newbie and this helped me so much, very easy to understand. Hope it helps

John Reed Home Page Collimation - Cheshire

[umadog]

"So in the first step I tried to center the secondary under to focuser and I used a white sheet of paper to block the primary to get red of all the reflections. "

I don't understand what you did here. The first step is to centre the primary in the secondary. You need to have the cross-hairs of your sight-tube pointing at the primary centre mark. This is achieved by adjusting the secondary. If you block the reflections you can't do this. You have to do this first, the order matters. Details here:

Telescope Reviews: Useful info about secondary mirror alignment

"I think that maybe the secondary should be offset on a f5 system? and is that why it is closer to the primary? Could I turn any other "

The offset will happen automatically if you collimate it correctly.

Your photo: the reflection of the Cheshire in the secondary is not right. Take a look at the images in that thread I posted. It contains very clear images of what it should look like. Finally, don't forget that the process is iterative. Go back to the begin and start again until everything looks as it should.

[yeti monster]

I believe any offset is refering to offset from the axis of the scope. The secondary aught to be centred under the focuser. To move this away from the primary the 3 collimation screws need to be slackened slightly, this will allow the positioning screw to draw back the secondary carrier. Do this in stages, whilst holding the secondary carrier steady to prevent it turning. Once the secondary is in position, then you can start to collimate the scope by getting the secondary to look circular through the focuser and having the primary clamps visible as per all the tutorials. A laser collimator helps to show that the secondary is well positioned by getting the laser to hit the primary in its centre. Once this is done, then adjust the primary collimation screws to bounce the laser back up to the origin. This should put you in good shape to then perform a star test. With a Cheshire, you won't have the benefit of the laser to guide you, so you'll just have to eyeball it.

Note, make adjustments to the secondary with the OTA sitting horizontally in the mount, in case you drop an Allen key etc.

[umadog]

Yeti, I don't know if we're talking cross-purposes, but I reckon you're referring to the so-called "classical offset." The other way is to move the secondary slightly toward the primary and tilt the optical train. This is the form of offset which will happen naturally as you collimate. You do not need to "try" to do this. It's described here: Passive Tool Collimation and the Newtonian - Article

[TheThing]

The first step is to line the secondary up with the ficus tube. Only touch the primary AFTER this has been done.

Try Andy's Shot Glass (pop it into Google) for the clearest guide to collimating ever. If you can't collimate after watching this video, you've no hope!

TheThing

Sent from my iPhone using Tapatalk

[ThomasBR]

Hi, thanks for you comments and links. Somehow I failed to realise that the collimation skrews on the secondary should be loosened before I could move the secondary. I think I have managed to do that now.

I was actually sing the guide fron John Reed (and the one from Astro Baby) - quite good illustartions indeed. I also ran through the video on Andy's Shot Glass, I think I have gotten it so there is hope :-)

Now I am waiting for clear skies to make a star test.