Cheshire Collimator advice

[BlueBird]

Hi,
I am looking for advice in purchasing a good cheshire collimator.
2 items available at Bintel:
1/ Bintel chesire
2/ Orion collimatoing tool.

any thoughts?

The tool will be used in a 76mm reflector and a 200 mm reflector.

Thanks Marty.

[erick]

My experience:- I asked at Bintel for the Bintel Cheshire. I was advised not to buy it but rather the Orion Collimating tool, which I did. (The staff members were quite convinced the Bintel tool was of unsatisfactory performance.) I have to admit, however, that I have never really made much sense of the view through that tool. I never put it in until I was collimated with the laser or barlowed laser and the Orion tool seemed to say it was spot on. However, recently, I was able to put a different Cheshire tool into my scope and the difference was significant. I could understand what I was looking at and crosshairs were in much better focus. I was told that Cheshire was from Andrews Communications. I've just looked at their site and it must be this one:- "Collimation eyepiece, Cheshire Newtonian type, Skywatcher brand" - $49. I look forward to hearing other comments.

[rmcpb]

Make sure the cheshire eyepiece you get is a LONG one. If it is too short like my original one you cannot see the hairline cross well enough to use the thing. I have the Orion one now and its worth the extra $20 over the short one.

[Kokatha man]

rmcpb - are your comments at variance with Erick's? I thought he was saying that he found the Orion tool less useable than the one he used recently, that he thought came from Andrews Comm....(Erick, were you referring to what is generally called the orion collimator/sight tube ?)

Bintel recently gave me the same comments re the chesire they stocked - they've slashed its price but think it's an inferior device and not worth buying (how's that for product un-endorsement!)

Personally, I'm sick and tired of "collimating" my newt with a modified film canister!!!???!!! (I use the word "collimate" very loosely, even though I think I've achieved marvellous results with this crude device in the short time I've had my 10" dob.)

Bintel tell me (constantly) that their next shipment is imminent: I'd be very interested to hear some views on the qualities/effectiveness of collimators that are currently available have read - I'm also waiting for a laser job but understand they are best for fine-tuning collimation.

On another note, what's your take on the Round Table Platforms rmcpb? - I'm awaiting delivery in a few weeks of one myself.....regards, Kkm.

[erick]

With regard to Bintel, yes, that was my experience.

The Orion collimating tool is a combined sight tube/Cheshire.

I can only say that the person with the Andrews' Cheshire looked through the Orion and said it didn't look very good, then brought out his Andrews Cheshire (which wasn't as long as the Orion as I recall), and we both agreed it provided a much better view.

However, I'm quite willing to accept that there is something wrong with my eyes :D

[rmcpb]

I just happen to like the longer tube as it lets me see the crosshairs clearer. However, I only use the Cheshire intermittently as I use the laser collimator for the checks before observing. The Cheshire is mainly used for centring the secondary and to check the overall collimation occasionally.

[Starkler]

The function of the crosshairs is to help get the secondary correctly aligned and a longer one is going to do this more accurately.

[ausastronomer]

Hi Erick,

The staff at Bintel are correct. The Orion Collimating tool is a great device, only bettered by specialist "optical" collimating devices like the Catseye and the Tectron Tools, which are infinitely more expensive.




Nooooooooooooooooooooooooooooooo !!!!!!!!!!!! :)

The Skywatcher combination cheshire is of clearly inferior quality to the Orion tool, which is Japanese made. The tolerances and machining on the Skywatcher tool are average at best and it will never be as accurate as the Orion tool, primarily because it will have a fractionally different orientation each time it is put into the focuser. In addition the Andrews tool is shorter and you also lose accuarcy as the tube length gets shorter. I have owned the Orion and also own the Tectron Tools, which are superb.

Persevere with the Orion tool, it is a very good unit. It just takes a little getting used to with all those reflections going on. That all comes with experience. You are driving a Ferrari and you are still on P-plates, pretty soon it will all "click" and you will get the gearchanges right :)

Cheers,
John B

[ausastronomer]

Try staying back from the orion tool a little more. I bet you are getting your eye to close to it. Nothing wrong with your eyes, it's your technique.

Cheers,
John B

[erick]

Thanks John, I would not be surprised at all that it is my technique. I've done some more reading ( http://www.propermotion.com/jwreed/ATM/Collimate/Chesire.htm ) to properly understand what I am trying to achieve with the Orion tool and I believe I now do understand, particularly the role of the reflecting surface on the Cheshire. The instructions that came with it weren't crystal clear to me. I'll re-read them tonight and I will probably now understand them as well :doh:.

With my 8" f6, the laser collimation has always been so quick and apparently successful, I haven't worried about anything else (apart from initial sight tube checking). With the new 12" f5, I'd better improve my capability! Eric :)

[erick]

Well, that's a pretty definitive comment! :)

[Cluster]

I bought my first real scope last week (GSO 6" reflector) and found collimating to be tedious, so I decided to buy some tools from Andrew's. Not having used anything before I grabbed both the $49 GSO laser collimater and the $49 Cheshire Newtonian, Skywatcher brand. I didn't know which I'd like better and find more useful (some tutorials recommend against using lasers for the secondary, others say it's fine).

The GSO laser is a nice piece of work and despite having a rather broad laser beam, collimated my telescope easily.

I honestly felt ripped off when I opened the Cheshire's box. It looks extremely cheap (all plastic), the rubber around the top is uneven, there is no sighting cross and the silver reflecting surface looks like it was sprayed on using $2 spray cans. A used film canister would be as useful and infinitely cheaper. $49? no way.

I expected a sighting cross and I guess my inexperience showed. The GSO laser is so easy to use for both the secondary and primary that honestly I don't know why anyone would use something else.

Anyway, that's my experience :-)

[Kokatha man]

Hi cluster, I reckon you're right about that Andrews chesire - they actually put one in with a parcel they sent me yesterday: could have been accidental but I reckon they're trying to get rid of them - I took one look at it after thinking I'd got a lucky dip and thought "nah - I'll stick with the film canister for now....!"

Pity you had to pay for yours - want another to keep it company?

[Geoff45]

Because a cheshire is more accurate and a barlowed laser (google this) is even better. A straight laser relies on the laser spot hitting the centre spot of the mirror exactly. If you are 2 mm off, then your error at the eyepiece is 4mm--way too much for an f5 Newt. See the very informative article here (http://gmpexpress.net/~tomhole/blaser.pdf) originally published in Sky and Telescope, which also describes the barlowed laser. For mine, the BL is the easiest and most accurate way too go, but a Cheshire comes pretty close (I use the Orion and find it's OK).
Geoff

[GeoffW1]

Hi,

Another Geoff chiming in here, I have both these gadgets, and use both, and agree wholeheartedly.

I have to be careful here because I recently got involved in some depressingly acrimonious exchanges (all very unnecessary) through wanting to stick to my guns, but I think that there is a LOT of variability in this:

- Dobs respond better to some techniques than others, do you think?
- Some Dobs (from what I read) are more sensitive than others, is this true?
- Some of us place more importance in certain collimation areas than others

How many think N O Carlin is the final authority for collimating Dobs (I think myself it is hard to fault him) ?

Cheers

[ausastronomer]

Well the GSO laser might be very easy to use but unfortunately life isn't that easy :)

You cannot properly collimate a telescope from scratch, with just a laser only. The laser cannot help with setting the secondary distance from the primary mirror. You can only do this with a sight tube or if you're good, eyeball it. Unfortunately things get worse, if the secondary/primary distance is not correct it is still possible to adjust the tilt of both mirrors and get the laser striking back perfectly upon itself, thus making the telescope appear properly collimated, when in fact it is not. Whilst the laser would show the telescope as collimated in this situation, a sight tube or star test on both sides of focus would show it to not be collimated. A laser is only useful to adjust the "TILT" of both the primary and secondary mirrors once the secondary is properly positioned in terms of its distance from the primary and in its rotation.

Once you have the telescope properly collimated a laser does an excellent job of adjusting the tilt of the mirrors. The barlowed laser method is only useful for adjusting the tilt of the primary mirror.

The best test as to whether your scope is properly collimated, is to check it with a bright star. I always do this several times during the night as the mirror cools, or shifts slightly with sling movement. A defocused star image on either side of focus contains an enormous amount of information about the scopes collimation and its optical quality. I don't need to go into all that here as Dick Suiter wrote an entire book on it. In very very simple terms follow whats bellow:

Use an eyepiece giving 10X to 15X per inch of aperture, if seeing will allow, less power if not.

Defocus the same distance both sides of focus until you get a diffraction pattern showing "rings". The diffraction rings should appear "PERFECTLY CIRCULAR" and not egg shaped. The secondary shadow should be perfectly centered in the diffraction rings on both sides of focus. If the secondary shadow position in the diffraction pattern appears to change from one side of focus to the other, the secondary position is incorrect in its distance from the primary. In other words, it is not properly aligned with the focuser.

Cheers
John B

[ausastronomer]

He is obviously a person very skilled in optical theory and the properties of light. So far as being an authority on collimating a telescope, he is an authority to people who need some assistance in collimating a telescope and in many cases don't properly understand it. A lot of experienced observers still do it the same way they did it, long before Nils Olif came along with his S & T article, me included. I am sure my telescope was properly collimated before that article came along.

Vic Menard, who is still around and a Cloudy Nights contributor, wrote a lot of articles and a book on collimation, before Nils Olif found his red laser. I doubt that Vic Menard needs to use a barlowed laser to collimate his telescope.

Come to think of it. I doubt Isaac Newton ever had a laser; and he obviously figured out how to collimate his telescope :)

Nils Olif's barlowed laser method is very good for quickly checking the tilt of the primary mirror, once you have everything else properly aligned. Keep in mind that's all the barlowed laser method is good for. Does it do this single job any better or more accurately than can be achieved with other methods? The answer is no.

Cheers,
John B

[GeoffW1]

Well, that's poor old Nils put in his place! ;)

More seriously. you don't think then that he can lay claim to some small incremental improvements over his forerunners?

Cheers

[BlueBird]

Thanks All who have contibuted.

I personally have not been able to get good results from using my film canister, and wanted to get an improved technique and tool, or is it an improved tool and technique.

From the discussion and 2 web addresses a site tube is an important first step.

The Orion combitation site tube and cheshire collinator is what I will be looking for.

Thank you all. Marty.

[ausastronomer]

The answer is probably yes; and I don't mean to be denigrating to him.

But I truly don't believe its heading things down the right path, in terms of properly educating new astronomers in how to set up their equipment. Collimating a telescope and setting it up properly is all part of the learning curve. By leapfrogging, a lot of beginners miss vital parts of that learning curve and don't ever understand the processes and theory behind proper optical alignment of all the components, namely, focuser, secondary mirror, primary mirror and the many different ways each of these components can be adjusted and the effect of those different adjustments. In my opinion it is somewhat akin to putting a 16 yr old in a new Ferrari before you have taught him how to change gears.

How do people who only use a laser or barlowed laser go when they drop the laser on the ground and break it, as they get it out of the car, prior to collimating the telescope? Do they pack up and go home for the night without observing, or just observe for the night with a poorly collimated telescope?

Use it as a means to save time once you know how to collimate a telescope, but don't leapfrog the steps in the learning curve along the way.

Cheers,
John B

[GeoffW1]

Hi,

Very well put, and I am obliged to agree completely.

I guess I must put away the laser every so often and see how I go with the Cheshire tool. Hmm, hard times ahead :thumbsup:

Cheers

[Karlsson]

I actually put this to the test a few months ago - I deliberately pulled my secondary out by about 4 mm and tweaked it out of the optical centre - the laser result could still be made perfect while the scope was plainly unusable.

Like John I have always relied on sight tube and star test - also because a star test reveals much more than collimation errors - it's the ECG of Newts so to speak (pinched optics, anyone?)

A few months ago I added a laser to the routine since it allows me to follow primary mirror adjustments real-time, rather than having to move from back to front - my kids all resigned as Vice-President of Collimation a long time ago...:sadeyes: But the star test still has the last word... make that a veto.

So while a laser collimator may be convenient, do not be fooled by the false sense of accuracy the word 'laser' may convey - there is no such thing as a free collimated lunch...:)

Each to his own - some tools are indeed easier to use than others... and I took vernier calipers to the shop when I bought my sight tube, too. If you learn how to judge the star test it does not have to be expensive - or tricky, for that matter...

[Cluster]

I will try the barlowed laser method and see how it goes. I haven't adjusted the distance between the primary and secondary simply because the secondary center screw is very tight on my 6" GSO and didn't want to budge.

There's a variety of opinions on collimation methods so when I have time I'll work through them and see what works for me.

[ngcles]

Hi BluBird & All,

Particularly agree with the comments by John B above.

FWIW, nowadays I've gone back to a good ol' combination sight-tube and cheshire. I used a laser for 2 years but twice the batteries let me down when I was alone in the dark somewhere remote. No batteries needed for the cheshire! In addition, It took me hours to collimate the laser itself and I was never totally confident it held its own collimation perfectly week-to- week, month-to-month. Cheshire itself never needs collimating!

Get one with the long sight-tube for the reasons stated above.

Make sure the fit in the focuser is very "snug" with as little side-to-side wobble as possible.

Are some dobs more sensitive than others? You bet! The smaller the f/stop number, the more twitchy it gets. An f/7 can tolerate slight miscollimation much, much better (ie less noticeable) than f/4.5 (or even f/4 etc).

Using a bright star as a double-check is also good advice (above by John B). Make sure you _also_ examine the image on either side of, but very close to focus for eccentric extra-focal rings etc.

Collimation is like riding a bike -- soon you won't even think about it while you are doing it and it will take only a minute or so to be spot on!

Best,

Les D
Contributing Editor
AS&T

[BlueBird]

Hi all,
rang Bintel to see about availabilty of the Orion tool and wound up having one delivered on thursday. stock just in.
Read John tweed`s web site and read instructions. 2 days later still trying to get it right.
I`m hoping that after the secondary is in the right place, I wont have to touch it again.
Of the 2 scopes at my place, one a 200mm diameter, 800mmfl the secondary is too large for the tool to see the outer edge. had to resort to putting a block dot in its centre to aid alignment. The spider is unadjustable so offset could be a problem.
The second is a cheap 76mm and its focuser tube doesn`t allow for complete insertion of the tool, althought its spider is very adjustable.

Maybe a shorter tool should be considered for scopes with specific mechanics.

One observation you may confirm, the crosshairs are out of focus when looking at the secondary. Is this expected?

thanks Marty.

[ausastronomer]

Hi Marty,

The secondary usually requires less frequent adjustment than the primary, but you should still always check the secondary at the start of each observing session. Unlike the primary, it will not move during the session, unless it is not properly supported.



Slide the collimating tool partly out of the focuser until you see the edges of the secondary, then tighten the eyepiece locking screw or collar.



You don't need this. The Orion tool is better than the short ones. Whilst it is designed for "about" an F5 telescope, it will work fine with your F4 telescope by drawing the collimating device out of the focuser just enough to see the edges of the secondary mirror.



Yes. When using the crosshairs you need to move your head back from the collimating device and look "at it", rather than "through it". Move your head back from the hole until the crosshairs go into sharp focus. This may be a good inch or even more. When you get it right and everything properly lined up (scope properly collimated and your head in the right place) you will be able to see the reflection of your own eyes pupil centred under the crosshairs of the collimating tool.

It aint hard, it takes a bit of getting used to. Be rest assured the tool you have will do the job very well, once you learn what you are doing. Patience and practice.

Cheers,
John B