Barlows & Collimators?

ballaratdragons (Ken) · #1 25-02-2005, 08:44 PM

Hi all,

It's question time.

Both Mombat and I need to know the same things.

Never having used either a Barlow or a collimator we need to know which is better.

<b>Barlow 2x:</b> Question - Short or long? and whats the difference?

<b>Collimator:</b> Laser or Cheshire? and whats the difference. I know one has a laser, but how does the Cheshire work?

We would both appreciate any help.

Striker (Tony) · #2 25-02-2005, 09:40 PM

I wrote this reply just so you got the email to check the response Ken.....sorry.....bit bored tonight....lol

Tonyhttp://www.users.on.net/~striker/laser.gifKen

ballaratdragons (Ken) · #3 25-02-2005, 09:48 PM

Yeah, I been counting the cricket sounds myself to this question.

I must have upset a lot of people.

Half the people in here know the answers.

RAJAH235 · #4 25-02-2005, 10:15 PM

Hi Ken and Mombat, All I can say is that I have the Meade #140 Barlow which is a long series. It is a top performer as far as I'm concerned.
The cheshire E/P,(about $60), has a large hole(25mm) in the side near the top and an eliptical alum. reflector inside,set at 45deg, with a 10mm hole in it. There is a 2mm hole in the top face which you look thru. By shining a torch into the side, you can see ALL the reflections. If your t'scope is correctly collimated, then your eye ends up in the CENTRE OF ALL THE CONCENTRIC CIRCLES.(with a little bit of 2ndary offset).
eg. Like a dart board.
As for the laser coll., they are prone to going out of collimation themselves. (Don't drop). They work by projecting the beam onto all the surfaces and finally disappearing up itself! If it doesn't, your t'scope isn't collimated. Not sure of pricing.
Cheshire can be dropped,(done), stood on,(done), and generally knocked around, but don't do this with a laser.
Maybe the others can comment on the diff. between long and short barlows, and their prefs. I never bothered. I looked for the most efficient and L.proof.
HTH. Regards, L.

ps. I think the short tube is mainly used on t'scopes with limited focuser travel.

ballaratdragons (Ken) · #5 25-02-2005, 10:43 PM

Thanks Laurie.

Do you have to look through a Cheshire or can you see it from the back end of the scope?

RAJAH235 · #6 25-02-2005, 10:49 PM

What sort of t'scope?????? You've got a DOB. You look thru the 2mm hole in the cheshire(1.25 inch diam), which is in the focuser.

ballaratdragons (Ken) · #7 25-02-2005, 11:11 PM

My 12" Dobber and Mombat is getting a 10" Dobber.

In other words I can't sit down the back end and adjust it looking up at the cheshire. Bummer.

RAJAH235 · #8 25-02-2005, 11:32 PM

Ken, how do you expect to see the mirrors and your eyeball if you are at the base of the t'scope? You put the cheshire into the focuser tube, you look thru the 2mm hole in the top of the cheshire. Then you shine a torch,RED LED, into the large hole in the side. This illuminates the mirrors so that you can see where your eye is. If it ain't in the centre of the dartboard (concentric circles), then your t'scope ain't collimated!(with a little bit of 2ndary offset). Check this link.

http://skyandtelescope.com/printable...rticle_790.asp

Starkler (Geoff) · #9 25-02-2005, 11:34 PM

You cant go wrong with a cheshire.
Its very easy to go wrong with a laser. In fact its pretty hard to be sure with a laser that everything IS right.

Id post a few usefull links but ive lost all that for now as my pc has died and im on a laptop

Bintel has the Orion Shorty plus for $150 I think, which is a highly recommended one and identical to the Celestron Ultima which carries typical Celestron pricing if you know what i mean .

ballaratdragons (Ken) · #10 25-02-2005, 11:50 PM

Thanks Laurie and Geoff.

I thought that a Cheshire might possibly work like the laser one where you can stay at the bottom of the scope and see into the side of the laser tube.

Looks like I'll have to go Cheshire and just keep moving up and down the scope.

I already have a film canister sight tube, I just want to get it more accurate.

Thanks guys

Starkler (Geoff) · #11 26-02-2005, 12:10 AM

Ken the ultimate measure of collimation is a star test.
How well does the film cannister go in that regard ?

RAJAH235 · #12 26-02-2005, 12:15 AM

Ken, It is easier if you get someone to do the adjusting for you, whilst you look at your mirrors/eyeball! You'll be there ALL night, if you do it yourself. Only minor adjustments are usually necessary. When you get to star test it, you definitely need 2. YOU have to keep moving the t'scope to keep the star in the centre of the field, while the adjustment is made! The reason I say this is, If the mirror is moved too far and the image moves off the axis, you will find it hard to get it back again without a drastic realignment. Please use 2 people. Your child can twiddle the coll. screws.

ballaratdragons (Ken) · #13 26-02-2005, 12:19 AM

Geoff,

I have not had clear skies in a week now. I'm still waiting to do a star test.

I just keep trying to collimate to perfection while waiting for some sky, and getting frustrated!

I know that I could spend weeks collimating, and it will alter soon as I carry the scope outside, but it's good practice. But would like to know the right tool to speed up collimating outside once the scope is set up.

Don't think we have clear skies for a while yet.

Starkler (Geoff) · #14 26-02-2005, 12:20 AM

agh trying to collimate a dob with a star test alone isnt an easy thing to do.
I meant use your tools to collimate then verify its accuracy later on a star test.

ballaratdragons (Ken) · #15 26-02-2005, 12:23 AM

Thanks Laurie,

Great idea. Kids or Missus (Cheryl). I did try a quick star test when I first got the scope. Bloody star had moved every time I got back up to the EP. lol

The trip from the bottom of a 12" to the EP is a long one. You need a packed lunch for each journey.

ballaratdragons (Ken) · #16 26-02-2005, 12:29 AM

Thats o.k. Geoff I knew what you meant.

I wouldn't dare attempt to collimate by star test.

RAJAH235 · #17 26-02-2005, 12:38 AM

Ken, did you try the link??????
L.

ballaratdragons (Ken) · #18 26-02-2005, 12:52 AM

Yes Laurie thanks.

I also printed that one off for a friend up the road a few days ago.

I must have not read all of it. I will re-read it in bed tonight.

RAJAH235 · #19 26-02-2005, 01:02 AM

Ken, your collimation shouldn't change just by moving the t'scope outside. I transport mine in the car like many others and my collimation doesn't change. It's a DOB, with a steel tube isn't it?
My Meade's got a SONAR TUBE. ie; CARDBOARD.

ballaratdragons (Ken) · #20 26-02-2005, 01:28 AM

Yep, steel tube!

It probably doesn't move but I would like to know that I can collimate quickly should I need to out in the dark.

The quick star test I did when I first got mine showed a set of perfect rings but because of the wind the image looked like it was boiling (air currents in the tube). I am eager to test it on a still night.