Using a Cheshire Collimator?

[Thirdway]

Maybe it's just me. I read Astro baby's collimation page and it's left me more confused than ever.

I'm struggling to understand why I needed a fancy Cheshire tool, if I can do the set up with a film canister cap with a hole in it?

I'm I missing something? Can I just use the Cheshire without using the film cap?

On the side of the Cheshire is a hole with some shiny metal cut at 45 degrees. There is no mention of where this is placed in relation to the scope, or what it is used for. Perusing a few web sites they mention shining a light in the hole makes setting up very easy at night......errrr how?

I have inserted the Cheshire and had a look through it. I can see solid cross hairs and also a ghost of cross hairs that revolves if I turn it in the focus tube. Also the central image goes from white to black like looking through a polarising filter as the tool is turned.

I can see the primary mirror circle with a black circle adjacent to it, all inside another circle.

This is on my Skywatcher Dob 200.

Any help would be great.

[damnut]

Hi There,

Couple of tutorials on youtube : -

1. collimate 200p - YouTube

2 . cheshire collimation - YouTube

Hope these help.

Cheers

Edited January 31, 2012 by damnut

[Thirdway]

Hi Damnut,

I already looked at all of them. No one uses a plain old Cheshire, they all use laser versions. I'm really wondering if the none laser collimator tool is even worth having if an old film cap does the same job? Seems like I bought a tool which has no real use? Probably should have splashed out for a decent laser.

[Grunthos]

No one uses a plain old Cheshire, they all use laser versions.

Mmmm, I've just bought a Cheshire after becoming disillusioned with my laser

[mrphildog]

Same here - I've been looking for a video of someone using a cheshire collimator but all the youtube vids seem to be using laser ones...

[Damo636]

The Cheshire part of the Cheshire/sighttube collimater is used for aligning the primary only and yes the film canister will do the same job providing you can see the reflection of the small hole. This is where the angled shiny surface of the Cheshire makes things easier. The orientation of the Cheshire/sighttube doesn't matter, just have the angled surface pointing at a light source. The crosshairs are used for aligning the secondary with the primary. Adjust the tilt of the secondary until the crosshair falls inside the doughnut on the primary. I use a laser but always finish by double checking with a Cheshire.

Edited January 31, 2012 by Damo636

[coulthamst]

To put it another way, the tool can be rotated in the focuser so that the shiny angled surface provides the maximum light available from daylght, or from a fixed light source. For a hand held light source the tool can be rotated to the most convenient position.

[Brent]

I am about to buy a collimation tool myself, but I can only afford one and I'm in two minds which to go for.

Is there anything that a well collimated laser (plus barlow) cannot do, that a cheshire can?

[aussi skywatcher]

Hi Guys, for what is worth I too have had problems with my Laser collimator and today I scrapped it for good and finally learnt to use the Cheshire that's been sitting doing nothing for 3 yrs - just followed Astro Babes article to the letter and all is fine. I have the skywatcher 8" dob and while I was messing about I fitted springs behind the primary mirror and a set of "Bobs Knobs" - so easy to adjust now - why don't manufacturers fit them on all models and not just the bigger ones? Just been out for a short session and the results of today show a marked improvement all round.

Cheers Paul

[Damo636]

I am about to buy a collimation tool myself, but I can only afford one and I'm in two minds which to go for.

Is there anything that a well collimated laser (plus barlow) cannot do, that a cheshire can?

The Cheshire/sighttube is the more complete

tool. The laser on its own cannot center the

secondary in the drawtube, this is where the

long sighttube part of the Cheshire comes into

play.

[Moonshane]

the reason for the collimation cap (rather than the cheshire) is that it gives a 'wider field' of view down the focuser, making the centralisation of the secondary easier to see/do.

once the secondary is the right shape and the right central position then you can fine tune with the cheshire.

other requirements are as above. if you need further help then just ask

[umadog]

The sight-tube portion of the combo tool is designed for centring and rounding the secondary. You can use the collimation cap for this purpose if you wish, but it's not designed for the job.

[Thirdway]

I'm sure Astrobabes guide works well for a lot of people, but I just find it confusing. Can I use the Cheshire to get the secondary mirror aligned as well as the primary. Better still is there someone local who can teach me how to do this?

At present, looking through the cheshire this is the image I see.

http://db.tt/lCkS1N8g

[umadog]

Damo has already answered your question You can use the Cheshire/sight-tube tool to adjust everything that needs adjusting. Some people do find the AB guide confusing, but that's partly because it covers everything in quite some detail. You may not need all of the information in it so the extra stuff may confuse. It's worth knowing about, though, as it is pretty complete. Take a look at these links: Rob Campbell's Home Page Pay particular attention to the second link, which is simple.

You current image shows that you're very far off. Take it slowly and one step at a time. Adjust the secondary tilt first until the primary mark is under the crosshairs. Then repeat and adjust the primary until the Cheshire spot and primary donut meet and are centred. Iterate back and forth between the primary and secondary until you're done. Use the third link on that page to correct secondary position in the focuser if needed.

Edited January 31, 2012 by umadog

[Tim]

I'm sure Astrobabes guide works well for a lot of people, but I just find it confusing. Can I use the Cheshire to get the secondary mirror aligned as well as the primary. Better still is there someone local who can teach me how to do this?

At present, looking through the cheshire this is the image I see.

http://db.tt/lCkS1N8g

That sounds like the best idea. You could do with learning the correct use of the tool.

The chesire EP will be more effective than a laser on its own for more reasons than one. It is very easy to think you have perfect collimation with a laser, ie, all the lights bounce off and end up where they should, but in actual fact the mirrors are all askew.

Cheers

Tim

[kniclander]

try "andy's shot glass" - it is not as thorough as Astro-baby's guide but it'll get you pretty well there and it is much simpler.

[Brent]

Thanks Damo, Moonshane & umadog.

Decision made

EDIT: And Tim as well - that sentence definitely seals the deal!

The chesire EP will be more effective than a laser on its own for more reasons than one. It is very easy to think you have perfect collimation with a laser, ie, all the lights bounce off and end up where they should, but in actual fact the mirrors are all askew.

Edited January 31, 2012 by Brent

[steppenwolf]

A Cheshire is by far the most versatile tool although there is a place for a laser collimator if you understand its limitations and the laser itself is correctly collimated - some aren't making them useless.

Tuition on the use of a Cheshire would make a lot of sense - to this day, I still refer to my notes when I use one!

[Thirdway]

It's annoying because I'm usually the 'go to' person when something technical rears it's head. It's not as if the process is particularly complex, align secondary mirror with eye piece and primary mirror with secondary mirror and there are half a dozen adjusting screws. Yet it still seems so obscure. I'm sure if someone showed me, it would make total sense and I would teach others.

[Moonshane]

The problem is you are looking at reflections of reflections so it does get confusing. the key adjustment is the primary adjustment as it makes the most difference to detail etc. If you can get it all smack on though you know you are getting the most from your scope.

[Thirdway]

So, in the photo I posted, what exactly is what? Is it secondary mirror position/tilt, primary position or are they all so far out I need to start from scratch.

[Moonshane]

is this a shot down the empty focuser or (as I suspect) a shot down the Cheshire?

either way, assuming your secondary is 1) showing a round shape (the shiny surface) and 2) central in the focuser tube you need to adjust the secondary adjusters until the reflected donut (see in the pic) is central to the cross hairs of the Cheshire (NB ignore the spider vanes).

then adjust the primary to put the black spot in the pic in the centre of the donut in the pic.

you are then collimated.

[Thirdway]

Yes, looking down the Cheshire.

So the shiny bit and donut?

I see a large white area, then a smaller black area, a smaller white area. Within that final smaller white area is a black dot and the centre circle on the primary.

This is why it is difficult. When I look at the Shot glass video it's straight forward, then I look down the barrel of the Cheshire and it doesn't look much like the image in the video.

If I can understand which bit is supposed to go where I can figure it out.

[Astro_Baby]

Colimation IS confusing. If you follow my guide to the letter all will be well. Thats why I wrote it to help people.

The confusing refekections are precisiely why my guide has you put some card donw the tube to mask the refelections in the firts stage of collimation.

Its very hard to explain collimation but easy to do. I tried to make it a step by step guide with each process broken down to its component parts.

Most collimation guides show the classic concentric circle pattern which you wont get with a modern newt. The simplified classic concentric view is the thing that most confuses beginners and thats

Recisely why I wrote the guide to take all factors in.

You need to read the guide and take it one step at a time. Your own cllimations is completely out of whack by the way. i would propose go back to firts principles and read either my guide or smeone elses and woek on it.

Dont be tempted to assume a laser will fix all ills, they are one of the biggest causes of beginners asking questions as to why it doesnt work and also a big reason for people having duff collimation. Without a high grade focuser ai would say they are a waste of time.

[Thirdway]

I haven't touched anything as yet, the scope came like that. I'm glad you said its all out of wack, at least that gives me license to fiddle. I will have another read through your detailed instructions again.

Edited January 31, 2012 by Thirdway