Cheshire collimator

[Dujon]

I wasn't too sure where to put this so have plumped for this subject. Originally I posted elsewhere so I hope I'm doing the right thing by moving it.


Given the many comments on this site regarding Cheshire collimators for Newtonians I've saved up a few dollars to buy one.

Finding one though is something different. I've come across this Orion unit from BinTel but, never having seen a Cheshire, I really don't know what I'm looking at. It's simply called a collimating eyepiece.

https://www.bintelshop.com.au/Product.aspx?ID=5508

Any assistance would be greatly appreciated.

[Starkler]

Yep thats the one !

Theres a competing unit made by Synta, but the Orion one is the better one.

[ballaratdragons]

I use the one from Andrews. It is very good too.

Collimation eyepiece, Cheshire type, black aluminium with cross-hairs $29.00

http://www.andrewscom.com.au/site-section-10.htm under the 'Andrews' listing, then scroll down to the accessories.

[RAJAH235]

John, that's called a combination Cheshire. Very good unit. You need that 'longer' one for your dob.:D L.

[Gargoyle_Steve]

I have the Bintel combination Cheshire / sighting tube, yes it's excellent, yes I use it in a 10" reflector, yes get it!

:P

[middy]

So we have one from Bintel @ $69 and one from Andrews @ $29.

This is a bit of a price difference. Are they exactly the same thing? Is the Andrews one a combination Cheshire as well or just a Cheshire? Not that I know the difference, I've just heard people say "Make sure it's a combination one".

[rmcpb]

I have both and NEVER use the $29 one any more. It is simply shorter and harder to use. Go for the longer one straight up.

Cheers

[Dujon]

Thanks, everyone.

Yes, 'tis a big price difference. Hmm . . . "now what to do?", thinks he. It seems there is strong recommendation for the dearer 'combo' unit.

So it's a 'combo'; a combination of what? I can understand the cross-hairs being of assistance when collimating a 'scope but I'm not too sure what the other facility is. Please excuse my ignorance. I currently have a laser unit from BinTel - I ordered it with the 'scope - but it's rather sloppy in my focuser/adaptor set up, no matter how tight I secure everything, so I really don't trust it.

I'm probably too late to place an order to have one arrive prior to the weekend so I'm in no rush. Accordingly any further comments and advice will be gratefully accepted.

*edit*

Oh, hello, Rob. Your post popped up whilst I was a-pondering. Thanks.

[astronut]

Hi John, I'm new to reflectors as well, after 30 odd years of using refractors.
I was told by a wiser person than me to buy the combo Orion unit from Bintel.
The reason being, you use the cross hairs at the bottom of the tube to line up your secondary spider. You adjust the secondary collimating screws until the hairs are superimposed onto the spider.
The view beyond the crosshairs is your centre spot from the primary mirror.
You then adjust the primary screws until you centre the spot in the collimation e/p.
I hope I've made this clear enough:lol: if not let me know. Cheers, John.:thumbsup:

[Dujon]

Thanks, John.

With the distrust of my current collimating tool I've taken to standing back from the focuser and attempting to align the secondary holder by eye within its boundaries. Then I've lined up the centre of the primary mirror with the reflection of my eye's pupil.

Should I then (thinking that I'm close) use the laser to check then I find that the laser reflection doesn't even hit the secondary! I'm a failure, I tell you, a failure.

Hence the need for assistance with a Cheshire. I do not wish to fork out a (to me) significant number of dollars only to find that whatever I purchase is as deficient in capability as is my current unit. The latter has been relegated to use as a pointer when viewing images on a television or computer screen, which purpose it serves quite well (though a bit heavy on batteries).

[astronut]

Well apart from being a simple instrument, it does not require batteries:lol: :lol:
Here is the instructions that came with the tool, there the clearest I've ever seen :lol:

[astronut]

Here are the instructions for the Orion Collimator.:thumbsup:

[Dujon]

Right, after much soul and pocket searching the deed has been done. I've ordered the Orion unit.

Again, to each and all of you, thanks for your input.

[Starkler]

The difference between the Andrews and the Orion one is length.

The "combination" refers to a combined cheshire and sight tube. The Andrews one is too short to be used as a sight tube. The sight tube is used to align the secondary under the focuser.

[Dujon]

Thanks, Geoff, I'd sort of worked that out in my own mind but wasn't too sure. It's nice sometimes (comforting even) to have one's own mental machinations confirmed.

Ah well, here's to a non-wobbly-bobbly Cheshire. :cheers:

[ballaratdragons]

John (astronut),

Is it possible for you to post the image of the cheshire instructions again, but only larger so we can read it please?

I don't have any problem using my Cheshire but it would be nice to read the correct recommended method.

Thanks :thumbsup:

[janoskiss]

Ken, you can download manuals from Orion's website (under customer support -> product instructions). They have downloadable manuals for most of their products. :thumbsup: Here is the one for the collimating ep: http://www.telescope.com/text/content/pdf/inst_03640.pdf

[astronut]

Here it is:)

[bojan]

Is there any experiences with Bintel laser colimator?
Bojan

[Don Pensack]

Basically, you:
1.align the tilt of your secondary mirror so the dot on the center of your primary mirror lines up perfectly behind the center of the crosshairs. Then,
2.Align the tilt of the primary so the center dot on the mirror falls into the black area in the center of the bright annulus formed by the reflection of the inside of the tool.
When all is aligned, the center dot is in the central black area, centered behind the crosshairs.
This alignment will work fine at f/6 and longer. At f/5 and shorter, I would suggest adding another tool, the autocollimator to improve alignment even further, as the tolerances for misalignment get quite small as the f/ratio shrinks.

As for laser collimators, most inexpensive lasers are, themselves, miscollimated. Unless you have checked the collimation of the laser, I wouldn't trust it. Collimating with a miscollimated collimation tool results in.....miscollimation. Rotate the laser in the focuser. If the center dot wanders, the laser is misaligned.

Oh, one final thing: You always want to collimate the scope to where the eyepiece will be when viewing. Accordingly, always tighten the setscrew on the collimation tool before you collimate.

Don Pensack

[johnno]

Hi DON,
Welcome to the Ice In Space Community,and thanks for the advice.

I have read many of your Articles over the years,and

Hope you enjoy your time in this Friendly Forum.

Regards.
John

[astronut]

:welcome: Don, It's good to have someone of your experience on the forum. John.:)

[Don Pensack]

Thanks, guys. I probably won't post a lot, here. I'll try to keep my replies useful. This violates that rule, but hey, I gotta shake the hand of someone who welcomes me.
Don

[Dujon]

Blimey, the thing's turned up already! Can't fault the service.

I'll let you know what I think when the chance to play with it arrives.

[rmcpb]

John,

If your laser collimator is loose in the focuser have you tried some masking tape around the end to make it a snug fit?

Worth a try.

[Dujon]

No, Rob, not yet, though the thought had crossed my mind. My main concern with doing that was that the tape could finish up being compressed on one side, thus effectively 'tilting' the laser's beam and putting me off track.

I'll see how it goes with the Cheshire first and then have another muck around with the laser unit. I have a feeling (unconfirmed at this juncture) that there is too much tolerance within the 2" adaptor's internal and external dimensions - even when clamped down - which is/are causing my problem. The focuser is, I guess this is obvious, a 2" Crayford.

Wish me luck. . . Please?

[johnno]

Good Tip ROB,Well worth remembering.
Thanks.
John

[Geoff45]

These should be used with caution. Apparently well collimated scopes may in fact be way off. You really need to use the so called Barlowed Laser Technique. See http://gmpexpress.net/~tomhole/blaser.pdf#search=%22Barlowed%20las er%20carlin%22
Geoff

[Jupiter]

How do I collimate/calibrate a laser collimator?

[RAJAH235]

Hi Jupiter. Bit involved but,
1. Piece timber bout 3" x 2" x 12" long.(base)
2. 4 off 3" nails.
3. Hammer 2 nails into timber base at 45 degree angle, so that they overlap each other at about 90 degrees, hammer the other 2 nails at the required distance to hold the laser... You are making a 'V' block/holder/cradle/thingy...
4. Take outside & set-up about 6' from a blank wall.
5. Place laser in 'V' cradle.
6. Turn it on & slowly rotate the laser in the 'V' cradle.
7. Watch the dot on the wall. If it moves in a circle, it needs collimating.
8. Be very careful when doing so, as you can break the assy inside.
9. Adjust as nec. & keep rotating after each step.
10. When the dot does not move off centre, you're done.
HTH....:D L.
ps. All up costs = zilch.

[Jupiter]

Thanks Rajah, I did a search and found the same instructions, i am up to nubmer 9 and not having a lot of success, meaning I can't get the circle reduced, anyway its heaps cloudy here so I'll just plod along.

[RAJAH235]

Damn! n I was just going to post a pic. Glad you found the solution.
Just be careful with the adjustments....Back one off before tightening another...
:D L.

[Jupiter]

I reckon I've finally got it, thanks for the help Rajah.

[RAJAH235]

You're welcome...:D L.

[GeoffW1]

Hi,

Yes, just got one up from Bintel Melbourne (Sydney store was out of stock). I asked about the need for adjustment of the unit so the beam was true to the housing, and was told "Yes, we just did that".

It is easy to use, and comes with instructions which are clear enough, but after much research on the Net I decided to check the alignment of the unit. Attached is a photo of the little jig I built for the purpose.

I found the laser was 11' 27" out, or a 4 cm circle of wander at 6 m. I don't object to this, because there is no telling what knocks it took in the post, and this astronomy game seems to have a huge element of DIY and self-reliance. It just shows that it pays to check.

After adjusting the laser unit to true, I found that the telescope (a 200mm Bintel Dob) had been waaayy out. My next little project is to try the Barlowed laser collimation procedure of N. O. Carlin. It looks good.

Regards

GeoffW