collimation tools laser v cheshire.

[Scott]

ive had my scope for about 6 weeks now and i really need to get a collimation tool. the cheshire costs £34 and a baader laser is £55 (flo). forgetting the price, which is :-

1) easier to use

2) more accurate

I relly need some advice because i'm taking almost as long to choose a collimator as i did a telescope.

thanks in advance for your thoughts.

[DOBBY]

If the laser is out of alignment...your 'scope will always be out as well

I dumped the laser & bought a cheshire..but usually use an old film-case cap with a pin-hole in it

[RikM]

Cheshire

[Carbon Brush]

For my money, both have their place.

With a cheshire, you get a good feel for what is out of line. with a laser I find it less intuitive.

But, if you are trying to set the primary mirror on a long newt, you need a laser. Or an assistant. Or you are a gorilla! Your arms have to be long enough such that you can look down the eyepiece tube and reach the mirror screws/nuts.

I also find the laser very handy when checking a scope in the dark.

An off centre laser can be brought back into line. They usually have setting grubscrews.

[Moonshane]

personally, I prefer the Cheshire. I have three (all manual) tools for collimation.

1) home made collimation cap for checking the secondary and focuser are aligned properly.

2) Cheshire/sight tube for fine tuning the secondary

3) Basic cheap plastic Cheshire for aligning the primary

A single Cheshire would do 2)/3) and a home made collimation cap would do 1).

Well-aligned lasers are OK but I stopped using mine a while ago. No batteries with a Cheshire either.

I have long focal length scopes (two of them have 5 foot tubes) and it's OK on your own but you need to remember carefully what move you made and what effect this had on the view. It soon comes.

[Daniel-K]

chesire all the way

[jimmyjamjoejoe]

I prefer a cheshire. No worries about alignment, and allows you to sort the secondary easily too.

I can see how laser's could be good in the dark, though tbh i've never had a problem with the cheshire, i just use the internal light of my car, or moon, or even my phone. And as for needing gorrila arms, just look, then adjust, then look again, can't see how that's a problem...

It'd be nice to have a good laser for those tweaks in the dark, but a cheshire does so much more for so much less.

[Moonshane]

if you have a laser though and feel it's not accurate then after setting the secondary you can always use a barlow lens (i.e. insert the laser in the barlow and the barlow in the focuser). this then projects the shadow of the donut onto the slanted screen of the laser. centre this on the 'hole' and you have a collimated primary. this is very accurate.

[Scott]

hmmm. seems like its cheshire then. thanks very much for your replies guys. much appreciated.

[Tribal-Wolf]

I use a laser more than the cheshire because it's easier and I check the laser collimation often and it has never been out.

I think that people have been put off lasers in the past because a lot of them were inaccurate but even the cheap ones are adjustable now so you can easily make a tool that checks them.

As long as you ling up your secondary properly you can get away with using a laser more often than not.

[nowayjose256]

I recently gave up on the laser when I saw how badly out of line my laser was just by rotating it in the focuser.

The dot moved all over the place.

Got myself the premium Cheshire.

Yes it's a bit more fiddely and next to useless in the dark but I'm totally happy with it.

[Tribal-Wolf]

Sometimes it's the focus tube that's out. I made a stand to check my laser and it has never been out of true but if it was there are adjuster screws to set it up. I think it's much quicker to adjust the primary with the laser and if I double check it with my cheshire it is fine.

[Moonshane]

collimation, like many things, is about finding what works for you. if you do it your way and you get good, sharp and contrasty images then there's not an issue - keep doing what you are doing and enjoy the scope.

[knobby]

Sorry chaps, bit of thread hi jacking !

but its relevant ... do you know if the Skyliner 250px dobs secondary mirror should be offset.

Just checked the vanes and its about 1.5mm off centre.

cheers all

[RikM]

The offset is built into the secondary holder. The vanes should be equal.

[knobby]

Right! Lets get tweaking then ...

Thanks Rick

[benjii]

I've got a 300p flextube and I have 3 things I find to be vital to collimating quickly and accurately. An Orion precision centering adapter, my laser and my cheshire. It takes less than a minute to do the adjustments on the middle of Dartmoor with the laser, then I just double check with the cheshire and it's always spot on.

[johninderby]

The problem with lasers is that there are good lasers and there are cheap lasers but no good cheap lasers. In this case you definitely get what you pay for.

I use a Hotech and it is absolutely spot on. Check collimation with it and when I've later checked it with a star test there's no adjustment needed.

Of course you should check that everything is properly set up in the first place, focuser square, secondary properly positioned etc. but this should only need doing once then afterwards a good laser like the Hotech makes collimation a 30 second job.

John

[Tribal-Wolf]

OK, if a laser is accurate then it is accurate, it doesn't matter if it cost 10k or 10p. The cheaper lasers out there now are adjustable and therefore can be set up to be very accurate. I have a cheap laser and I have borrowed a 5x more expensive laser a few times too. On a rig both lasers were exactly the same when turned at a distance of 25ft in a small target area, there was no discrepancy but if that had of been then they could have been adjusted. On that info I will keep my said cheap laser and buy a decent EP. The collimation is always the same when checked with a cheshire after using cheap laser too.

Don't be fooled into thinking because it's cheap it won't work, that's how the Japanese made themselves successful in building cars, British cars were not cheap and you never got what you paid for lol unless unreliabilty was a luxury.

[benjii]

I think Hotech's are overpriced for what they are, it's cheaper to get an adjustable laser collimater and a centering ep adapter and you still get the same performance.

That method is arguably more accurate than using a Hotech as well. Due to the Hotech centering the primiary with the secondary to the center of the focuser, but when eyepieces are used they're off center due to the thumb screws. If you use a centering eyepiece adapter, it ensures both the laser and eyepiece are centered, therefore the light is perfectly focused into the middle of the focuser. However, in saying all that, I bet you none of us would be able to tell the difference between the different methods... just food for thought!

[Tribal-Wolf]

One thing about these precision centering adapters, I can see the advantages but if your collimator is fitted and used by tightening the two thumbscrews and then any EP you use is fitted into the focuser using the same two thumbscrews then won't it make little or no difference as they are both being lined up to the way they are going to be used?

[benjii]

Yes, I concur. However, the Hotech centers itself in the focuser in order to counter the inaccuracies of thumbscrews. Therefore, is in a different position than an eyepiece would be.

[Dipper]

Can anyone tell me what is the difference between these four Hotech collimators? Hotech Laser pointers < Alignment accessories < Telescope accessories (I mean the first four collimators) They seem to have identical descriptions and the only difference is the price. :confused:

[umadog]

The centering is a bit of red herring. It doesn't matter greatly if the tool (e.g. the laser) is exactly centered in the focuser, it can be off by a bit and all will be well. What does matter, on the other hand, is if it's tilted in the focuser. This is when it's important to have a good 2" to 1.25" adapter and a collimation tool which is well machined, so that it fits precisely into the focuser. 2" tools are generally better than 1.25" tools, simply because you don't have to mess about with the adapter.

You also have to remember that whilst there are always errors in collimation, there are also tolerances. There are many things which will throw off the alignment a little bit: flex in the tube, flex in the spider, the positioning of the eyepiece, the motion of the focuser itself, your ability measure the errors whilst you align, changes in temperature, etc. The question is: will these things be sufficiently severe to result in a noticeable degradation of the image? Being "collimated" isn't an all or nothing thing. There are tolerances, meaning that if you're out by a bit you just won't notice. These are the tolerances for high-power observing: http://www.catseyecollimation.com/Newtonian%20Axial%20Tolerances.pdf In that document, FAET is what you correct with secondary tilt (first pass of the laser or sight-tube cross hairs) and PAET is what you correct with primary tilt (Cheshire, return beam of the laser [not ideal], or barlowed laser). Note how much more sensitive the primary is to misalignment, compared to the secondary. So you goal is to to get as close you can and you accept the fact that there will always be slop due to factors that are hard, expensive, or impossible to control. So yes, it's true that the set-screws may result in some tilt or de-centering. However, if the scope star tests fine with a given adapter and you can consistently get good star tests then you're ok to go.

A useful exercise is to look at a planet on a good night (Mars is a suitable target right now) and progressively misalign your primary. Use your collimation tool of choice to will see how far out it has to be for you to start noticing the detail go away and the star tests to look horrible. Basically, a telescope with poor axial alignment will produce a more blurry image. You can then try re-collimating, and playing with the eyepiece set screws or even with different adapters. Unless you have a really crappy adapter, I doubt you'd notice the difference. The more accurate tools will measure errors smaller than you will be able to detect in a real-world test such as this.

[skyhigh]

Having recently taken delivery of the Sky-Watcher 250PX,this thread makes a good read as I'm about to check the collimation of my telescope. I bought the Cheshire Collimator based on good reviews from users of the same make and model of reflector.

Just trying to decide as which guide to use. The Sky-watcher instruction manual details the process in 2 pages, the Astro Baby's Guide to Collmination is 10 pages with photographs of the Cheshire Collimator being used.

Before I make a start, I would appreciate a pointer as to which way to proceed.