First attempt at collimation on a 200P Dob.

[Glyn80]

Hello everyone,

I've recently purchased a Skyliner 200P Dob as my first ever telescope and i've just had a few attempts at collimation for the first time (as daunting as it felt 🙂 ). I purchased a collimating cap and a Baader laser collimator. When i first collimated the telescope I wasn't convinced the laser was ever aligned perfectly straight/centered using the use two tightening screws in the focuser. So I also purchased a Celestron Twist and Lock adapter to try to ensure everything was straight/centered as it could be. I've had a few attempts to try and get it all perfect, I might even be going a bit OCD with it to be honest 🙂. I have taken a picture through my collimation cap with how it looks so far. I think the primary could maybe do with a very slight adjustment but i'm not sure if the secondary all looks as it should? It would be great if someone could just confirm how it all looks, so I then know for future reference that i'm actually do it right. Many Thanks!

Edited September 6, 2020 by Glyn80

[Astrid]

You can use a cross hair intersection as a guide (diagram found online).

The outlines of the focuser tube, secondary and primary mirrors should be concentric (circles with the same center), so your collimation cap or laser should land exactly in the center of those 3 circles (2nd pic). 

My opinion: if you're not that picky and already spent too much time collimating, I think it is ok (perhaps the primary dot could be a bit higher)

 

  

Another illustration: green as the end of the focuser tube, magenta edge of the secondary and red reflection of the primary. So when magenta and red are exactly in their circles that's when you have the best collimation.

Edited September 6, 2020 by Astrid

[Pixies]

Have a look at Astro-baby's guide:

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

If you want to get it well collimated to start with, I would suggest you get the secondary mirror aligned under the focuser, first. Have a look under section "
Collimation Step 2 – The Secondary Mirror / Focus Tube Alignment" in the guide above (the bit with the coloured paper). Once that's done, you won't have to do that again unless you have to remove the mirror.

In the Seronik guide: https://garyseronik.com/a-beginners-guide-to-collimation/

he states that as long as you can see the whole of the primary (and clips) and the eye-hole is centered within the doughnut, your collimation is close enough to be very useable. Your is nearly - you just have to fine-tune the primary to get the eye-hole centered, as @Astrid says.

 

My advice as a relatively newbie. Don't be afraid to get stuck in - you're not going to break anything (as long as you don't tighten anything up too tight). The more you learn about how it all works, the better at collimation you will become. Obv avoid touching the mirror. A cheshire is a great time saver - it works as a sight tube (to align the secondary), you use the cross-hairs to collimate the secondary, and the cap to align the primary.

 

[Glyn80]

Thanks for the great advice. The Astro-baby guide is a really useful, especially the tip of putting paper behind the secondary mirror so I can see it's actual shape, which has helped make sense of things. I'm getting frustrated with the laser collimator though. All was aligned up well yesterday but after using the telescope last night and checking the laser collimation today, its off it's alignment. The collimator cap's view hasn't changed and the primary mirror is better aligned as i've just tweaked it. So something seems to be causing a problem with the laser. I try to get all the screws tightened up evenly so ensure the laser is central but something isn't quite right, maybe it's the focuser?. I think I will give the Cheshire a go as @Pixies  suggested to align the secondary mirror, then at least i will know that's ok.

[Pixies]

4 minutes ago, Glyn80 said:

Thanks for the great advice. The Astro-baby guide is a really useful, especially the tip of putting paper behind the secondary mirror so I can see it's actual shape, which has helped make sense of things. I'm getting frustrated with the laser collimator though. All was aligned up well yesterday but after using the telescope last night and checking the laser collimation today, its off it's alignment. The collimator cap's view hasn't changed and the primary mirror is better aligned as i've just tweaked it. So something seems to be causing a problem with the laser. I try to get all the screws tightened up evenly so ensure the laser is central but something isn't quite right, maybe it's the focuser?. I think I will give the Cheshire a go as @Pixies  suggested to align the secondary mirror, then at least i will know that's ok.

Make sure the secondary mirror is rotated around so that the 'circle' it presents to your eye is an actual circle. Use 2 sheets of paper as per AB. It looks like it needs to be rotated from your pics above

 

Edited September 6, 2020 by Pixies

[Glyn80]

From what i've read on AB'S site, am I understanding it correctly that the secondary mirror is rotated by just using the three tilt adjuster screws?

[Pixies]

You can back them off slightly, or just back off the middle screw. Either way will release the pressure on the secondary holder. 

The former obviously pulls the adjusters away form the holder. The latter releases the holder and it moves a little down the tube. Effectively, the 3 adjusters push against the centre screw. You can use either, since you will be doing the reverse to tighten things back up again, anyway.

[Glyn80]

OK that's great, thanks for your help much appreciated!

[Pixies]

Stick a photo up here once you've had a shot. We can run an app called Mire de Collimation to check the concentricity of the secondary.

[Glyn80]

I've just had a go at fixing the rotation. In the end I just rotated the holder by hand as I had to adjust the lenght of all the adjuster screws as one of them seemed to be putting a lot more pressure on the holder. To my surprise it was easier than I thought and nothing fell off 🙂 I've attached two photo's. Before and After and I think it looks better now.

 

[Pixies]

Hi. 

If you have a Cheshire, you can use that as a sight-tube to try and centre the secondary under the focuser. Otherwise, here's teh abobve image with a reticle imposed over it to help show you how it's lined up:

The reticle is made by an app called Mire de Collimation. You can get it here: (towards the bottom of the page)

http://sweiller.free.fr/collimation.html#chapter5

 

[Glyn80]

Thanks for the link. That software looks good and it clearly shows the secondary being off centre. I will have a go at adjusting that next, once I get a Cheshire.

[Glyn80]

Hello,

I've finally bought a Cheshire and have been using it today. This is how I have ended up with the collimation. I think it's looking ok. I can see the three primary clips (but only when i'm fully racked in) and the primary mirror seems aligned. I had to centre the secondary a bit as well.  Any opinons greatfully received, thanks.

[Pixies]

Hi. Hard to see exactly - but it is tricky to get everything visible and in focus in a photo.

You need to start with the coloured paper - and make sure that the secondary is rotated and aligned under the focuser so that the outside circumference is concentric  with the end of the Cheshire. Like this:

Nezt you remove the papers and then use the secondary adjusters to fine-tune the tilt of the secondary until the doughnut is under the cross-hairs. This means the secondary is now aligned with the centre of the primary (you don't have to worry about seeing the mirror clips when using a Cheshire)

And finally you adjust the primary so that the little black dot of the eye hole is centred within the doughnut. You will need to make sure the side-port of the cheshire is illuminated, so that the eye hole is contrasted against the bright side-port.

Does that make sense?

 

[Glyn80]

OK yes that makes sense. I've been focusing too much on being able to see the three primary clips rather than lining up the doughnut with the cheshire's crosshairs. 

[Pixies]

6 minutes ago, Glyn80 said:

OK yes that makes sense. I've been focusing too much on being able to see the three primary clips rather than lining up the doughnut with the cheshire's crosshairs. 

yep - that's for doing it with a simple collimation cap.

Bear in mind - the secondary alignment stage is not done very often. It should only lose alignment after a knock, disassembly, etc. Although you should check it occasionally. It's the final adjustment of the primary that is done more often.

[Glyn80]

That all makes sense, I couldn't understand why my laser collimator was out by so much after using the Cheshire. Now I've centered everything properly using the Cheshire, the laser lines up as well now. Thanks for your help, much appreciated! 

[Pixies]

Clear skies tonight? Let us know how it goes

[cletrac1922]

On 07/09/2020 at 00:33, Glyn80 said:

Hello everyone,

I've recently purchased a Skyliner 200P Dob as my first ever telescope and i've just had a few attempts at collimation for the first time (as daunting as it felt 🙂 ). I purchased a collimating cap and a Baader laser collimator. When i first collimated the telescope I wasn't convinced the laser was ever aligned perfectly straight/centered using the use two tightening screws in the focuser. So I also purchased a Celestron Twist and Lock adapter to try to ensure everything was straight/centered as it could be. I've had a few attempts to try and get it all perfect, I might even be going a bit OCD with it to be honest 🙂. I have taken a picture through my collimation cap with how it looks so far. I think the primary could maybe do with a very slight adjustment but i'm not sure if the secondary all looks as it should? It would be great if someone could just confirm how it all looks, so I then know for future reference that i'm actually do it right. Many Thanks!

 

Glyn

Why did you need to touch the collimination in the first place

Were you unable to focus of objects such as Jupiter, Saturn, and other DSO's

Lot of people on here get themselves into more trouble than Ben Hur, with respect to collimination

It is such a simple process, and I use a laser colliminator, and takes me less than a minute to do

Unless you are transporting your Dob, to different locations, then might to need occasionally to colliminate

Pre Covid-19, I was out a couple times per month doing presentations in primary schools, Space Badge, cubs and joeys scouting movement, and my 10" Dob travels on the backseat of my SUV

Your Dob should had been set correctly when you took delivery

Provided you do not bump the Dob on doorway when setting up, neither the primary or secondary mirrors will be out of alignment

First of all, set the secondary, using laser colliminator on low power, so that the red dot is in the center of the primary, which has a small dot

Then slightly loosen the locking screws, and adjust the primary, so have no image center of the target of the colliminator

Then tighten the locking screws, ensuring the primary stay centered in the target of the laser colliminator 

When taking pics of primary and secondary mirror, you cannot be fully centered, hence my look different to what really is

Some time ago, had a new club member turn up one night to club meet with a 8" flex Dob had brought second hand

I could not get collimination right

Using a bit of paper, I checked the veins, and found that the secondary mirror was to one side

Adjusted the veins to center the secondary, then was able to do collimations in  a couple of minutes

The new member and his family were over the moon, as able to use the Dob for the first time

John

 

 

[Glyn80]

On 19/09/2020 at 17:15, Pixies said:

Clear skies tonight? Let us know how it goes

I managed to get out tonight to see how the collimation had gone, even though it was a bit breezy with some cloud. I was able to see Jupiter and it's belts and all seemed to be in focus. Even better was Saturn, I was able to see a black line separation in the rings and I even noticed a slightly darker band going around the middle of Saturn. Finally I moved onto Mizar and Alcor and I was clearly able to see Mizar B closely adjacent to Mizar. So all in all everything looked good (well from a novice's perspective it did), i'm assuming if my collimation was poor, I wouldn't be able to see the details on Jupiter and Saturn? 

[Pixies]

21 hours ago, Glyn80 said:

I managed to get out tonight to see how the collimation had gone, even though it was a bit breezy with some cloud. I was able to see Jupiter and it's belts and all seemed to be in focus. Even better was Saturn, I was able to see a black line separation in the rings and I even noticed a slightly darker band going around the middle of Saturn. Finally I moved onto Mizar and Alcor and I was clearly able to see Mizar B closely adjacent to Mizar. So all in all everything looked good (well from a novice's perspective it did), i'm assuming if my collimation was poor, I wouldn't be able to see the details on Jupiter and Saturn? 

If you can see the Cassini division in Saturn's rings, I think your collimation is spot on.

Why not try this:

 

[wookie1965]

Be careful with laser collimators the cheaper ones can need collimating. 

You can use the laser even if it's out with a Barlow lens you will see the primary mirror will be seen in the 45° surface just line the circles up. 

I have always used a Cheshire sight tube cannot beat it.