Reccomend me a collimator for sw 300p dob

[djpaul]

Need advise on which collimator to purchase for my 300p dob.

There seems to be a big diffence in costs of collimators

Regards paul

[wookie1965]

Don't buy a cheap laser usually always need collimating themselves,  saying that if you do get one and get it as accurate as possible you can then use the Barlow method which with a long scope will make it much easier. 

Other than that get a Cheshire/Sight-tube cannot go wrong with them. 

[RT65CB-SWL]

I have a Baader and a HoTech.

The cheaper ones may/will need collimating before use. I had one and was way off target and it 
would not get anywhere close; even when collimated and tested alongside the other two as above.

[Trikeflyer]

I’ve always fancied one of these. Never used one but if I was looking for a first one, I’d definitely have one of these

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Concenter-2--colimation-eyepiece-for-Newtonian-Telescopes.html

Steve

[Mark S W]

I use the Farpoint 650nm laser collimator. Easy to use and accurate 

 

[Captain Scarlet]

22 minutes ago, Trikeflyer said:

I’ve always fancied one of these. Never used one but if I was looking for a first one, I’d definitely have one of these

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Concenter-2--colimation-eyepiece-for-Newtonian-Telescopes.html

Steve

+1 for that, I have one, have lent it a couple of times and the borrowers have been amazed at how much more accurately and quickly they've been able to place the secondary than with anything else

[Trikeflyer]

Thanks for sharing that. Yes I might have to push the boat out and get one!

Steve 

[John]

I use one of these with my 12 inch F/5.3:

Cheap, simple and it works.

 

[Geoff Barnes]

8 minutes ago, John said:

I use one of these with my 12 inch F/5.3:

Cheap, simple and it works.

 

Yep, same here with my 12 inch f4.9 Dob. Fine tune the primary mirror with a star test using a high power eyepiece and all done. Cheap as chips,simple and effective.  

Edited June 11, 2020 by Geoff Barnes

[Barry-W-Fenner]

On the subject of 300p collimation.

Quick question, when I look down the focuser of at the secondary mirror I can only see two of the clips holding the primary. Does this mean the secondary needs tweaking so all 3 clips are in view?

Cheers

baz

[Barry-W-Fenner]

41 minutes ago, John said:

I use one of these with my 12 inch F/5.3:

Cheap, simple and it works.

 

What is this tool called chaps?

[johninderby]

Cheshire eyiepiece.

https://en.wikipedia.org/wiki/Cheshire_eyepiece

Edited June 11, 2020 by johninderby

[Geoff Barnes]

@Barry-W-Fenner I find my short Cheshire shows the primary clips better than my long one. Also racking the focuser right in and out until all three are visible helps.

[discardedastro]

I've found the Hotech lasers to be pretty good. I use the Barlow projection trick to confirm after a rough alignment with the unbarlowed laser.

1 hour ago, Barry-W-Fenner said:

On the subject of 300p collimation.

Quick question, when I look down the focuser of at the secondary mirror I can only see two of the clips holding the primary. Does this mean the secondary needs tweaking so all 3 clips are in view?

Cheers

baz

You should be able to see all three, yes. I found Astro Baby's guide great for this: http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Vic Menard's book is another great guide if you want to really dive deep: https://www.firstlightoptics.com/books/new-perspectives-on-newtonian-collimation-vic-menard.html

[johninderby]

One very usefull bit of kit is the Concenter. Simple idea but allows for perfect setup of the secondary. Once the secondary is setup perfectly the rest of the collimation is easy. Just level the primary mirror by adjusting the the colimation screws to the same length using a small steel rule and  you will be nearly collimated with only a minor tweek of the collimation screws needed. 

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Concenter-2--colimation-eyepiece-for-Newtonian-Telescopes.html

Edited June 11, 2020 by johninderby

[ScouseSpaceCadet]

+1 for the short cheshire and/or collimation cap. Super cheap, low tech and simple.

 

[Captain Scarlet]

The optical "tricks" for collimating a secondary only really make sense if the eye is placed at and only at the primary's (reflected) focal point. Because only from that point do features on the outer “surface” of the cone (ie the edges of either mirror) collapse to a perfect circle.

The two main optical tricks are:

- Getting the secondary to appear perfectly circular, even though it's actually elliptical.

Only from the focal point should this ellipse appear as a perfect circle.

- Getting the primary's mirror clips symmetrical and "just in view"

Only from the focal point should you just about see the edge of the primary. Rack in closer, and obviously you'll see more of the primary. Rack out a fair distance, if you can still see all the clips it means the secondary is larger than strictly necessary (not necessarily a bad thing, but you're trading off CO for illuminated field).

What this means is that one shouldn't really rack in or rack out to get better views of mirror edges, everything should be done with the eye at the focal point.

M

 

Edited June 11, 2020 by Captain Magenta

[johninderby]

Using a concentre makes it so easy to set up the secondary as your eye is centered and the circles on the concenters etched reticle show when the secondary looks circular. I now consider it an essential piece of kit.

[Ally8446]

1 hour ago, johninderby said:

Using a concentre makes it so easy to set up the secondary as your eye is centered and the circles on the concenters etched reticle show when the secondary looks circular. I now consider it an essential piece of kit.

I couldn't agree more. The Concentre is a fantastic piece of kit. I wouldn't be without one. Whenever I go to my dark site in the car the first thing I do is pop the Concentre in, just to check the secondary position. Rarely does it require adjusting but I do have to travel up quite a rough track. 

[djpaul]

Thank you for all your help so far.

So do i need a concenter and a cheshire?

Up till now ive only owned refractors.Mainly to avoid collimating..

Paul

[johninderby]

If you get the Concenter then no need for a Cheshire.

[djpaul]

Cheers john.

Am i right thinking theres a 2 inch and 1.25 version.?

If so is there a perference?

 

[bomberbaz]

7 hours ago, Captain Magenta said:

+1 for that, I have one, have lent it a couple of times and the borrowers have been amazed at how much more accurately and quickly they've been able to place the secondary than with anything else

thanks for the heads up, being the spontaneous type and having read reviews on CN it looks like it's worth having, button pressed. 

EDIT: I should add that I am soon taking possession of a truss dob. Secondary mirrors tends to hold well on solid tubes, this isn't the case so much for truss/flex tubes'

So I have bought this to use with a cheshire. If it works well, the laser I have will pay for the TS concenter.

Edited June 11, 2020 by bomberbaz

[johninderby]

34 minutes ago, djpaul said:

Cheers john.

Am i right thinking theres a 2 inch and 1.25 version.?

If so is there a perference?

 

The two inch seem to be popular but I’m using the 1.25” with the Hotech self centering adapter.

Edited June 11, 2020 by johninderby

[bomberbaz]

14 minutes ago, johninderby said:

The two inch seem to be popular but I’m using the 1.25” with the Hotech self centering adapter.

I bought the 2" version.  I have never been completely happy with the hotech adaptor.  My moonlight focuser had the  EP clamp ring right where the expansion, centring  part of the adaptor was. That's not going to help.