collimator tools

[Alfa Omega]

another newbie question.. which is considered to be the best easiest and most accurate to use of all collimators available esp for a newbie like myself.

also red dot finders which are considered the best most acurrate etc?. does the most expensive mean best, or are they all about the same. my guess is the more they cost the better or am i wrong going on that cheap = nasty, expensive is good.?

regards.Rob

[Astro_Baby]

This is a personal opnion only - get a Cheshire Collimator, they are cheap, reliable and ultimately the simplest and most accurate method.

If you go for a laser either buy the very best, ie the Hotech or expect aggro.

Others will argue that lasers are cool but my perception (and its is only perception) is that more questions are asked by newbies who get stuck with lasers and have problems than other methods.

Dont develope collimation paranoia also known as telescope hypochondria

Thats my two penneth on the subject.

[sixela]

another newbie question.. which is considered to be the best easiest and most accurate to use of all collimators available esp for a newbie like myself.

Ah, if you want the "best" (without any qualifiers) be prepared for quite a raid on your wallet...

Well, that depends on your budget. If you're thinking of the most complete tool that doesn't cost an arm and a leg and is well machined, it's probably the 1.25" AstroSystems LightPipe.

It's only let down somewhat by its instruction booklet, which suggests you centre spot the secondary and use the cross hairs to centre the secondary. In fact, it's a lot better to rack out the focuser until the primary reflection is just smaller in diameter than the outline of the secondary, and then to make the secondary's edge concentric with the inner edge of the tool.

If you have a more expensive scope and/or you plan to do photography and/or use a Paracorr there are other tools, and there are also more expensive tools that are more practical.

It's always dangerous to ask for the "best" tools. The absolute best is usually quite different from the "good enough".

--ONLY READ THIS IF YOU DON'T CARE ABOUT THE BUDGET TOO MUCH--

The best sight tube for scopes with 2" focusers is the CatsEye TeleTube, and if you buy one you might as well make it a combination tool (works like the AstroSystems Lightpipe) and make it a TeleCAT ($125, but with a template to put an excellent centre spot at the exactly correct location on the primary).

The most convenient tool for setting the tilt of the secondary is a good laser collimator, and really the best one out there is a Howie Glatter laser collimator (but at a steep $150). There are a lot of cheap ones, but frankly, if you don't want to spend ages collimating them first and hacking them until they fit well without play in the focuser, they're not really good tools; the cheapest good one is the Farpoint/Orion LaserMate Pro (not Deluxe!!) --its resemblance with a Howie Glatter is, I think, not really a coincidence.

For setting the tilt of the primary, if you want the best tool either get a CatsEye BlackCat Cheshire (there is one included in the TeleCAT, actually, but the BlackCat on its own is more convenient as you can actually carry it in a pocket and is slightly easier to illuminate at night) or a Howie Glatter TuBLUG for your laser collimator (not necessarily a Howie Glatter).

As you can see, it's easy to spend as much as the value of an 8" Dob on collimation tools so that collimation is both really precise and as convenient as possible (yes, I have all these tools), but you can also collimate with just the LightPipe...

also red dot finders which are considered the best most acurrate etc?.

If you don't mind the rather clunky appearance, nothing beats the Telrad (plus optional dew shield). What that gives you is a reticle with three circles (0.5°, 2°, 4°), and there are many star charts for objects with a TelRad overlay and many sky chart programs allow you to put a TelRad reticle on star charts as well.

But the cheap Skywatcher red dot finder is fairly functional, eve if its dot is actually quite large.

[sixela]

If you go for a laser either buy the very best, ie the Hotech

My personal opinion (I'll call you and raise you two penneth!) is that a Hotech is not "the very best". It's got a ghee-whizz feature that fixes a non-issue and sometimes introduces rather than fixes registration issues if it doesn't want to be friends with the focuser (having battled with a colleague's Hotech laser that doesn't register the same way in his SCT when he turns it, I should know).

I tend to regard the Howie Glatter laser collimator as "the very best" because it's very well machined, with no slop, a very long barrel and accurate shoulder to register even more precisely, and because it is built like a tank and will not even get miscollimated after you drop it and it chips a bit of concrete off the runway (true story --don't ask me.)

It's especially good coupled with the actual functional gizmos that either come with it (screen to read the centre spot silhouette in the returning diffraction pattern made by its aperture stop, for barlowless "barlowed laser" collimation) or can be purchased (barlowed attachment, BLUG, TuBLUG, holographic attachment, etc.).

A close second (and more than a bit a reverse-engineered sibling to the HG) is the Farpoint also sold as "Orion LaserMate Pro", which is light years ahead of the other cheap Chinese Orion laser miscollimators.

Then there's the Astrosystems, then the Kendricks, and only then would I place the Hotech.

And then there is the unwashed hordes of laser miscollimators; sometimes you're lucky, but often they'll be miscollimated, become miscollimated when you drop them or wobble in the focuser, useless unless you perform tricks of wizardry with V-blocks and bits of aluminium tape (once you go that route, you might as well build your own with a 3 GBP keychain laser, some PVC pipe, a plastic aperture stop made with a fine drill and a bunch of small bolts).

Your point is well made: often, especially for visual use if you have no Paracorr and aren't doing photography, a good combination tool ("collimation eyepiece") which is a combination of a sight tube and a Cheshire is more than "good enough". It's actually going to be less trouble than certainly an unreliable laser collimator.

[Astro_Baby]

I will bow to your experience of the glatter laser. I have tried two cheap lasers and the balder and found all of them worse than useless.

The only laser I have used to date which produces consistent results and didn't need messing with out of the box was the Hotech.

I avoided talk of the Catseye because although it's good it's probably overkill. I found even with an F5 scope a Ceshire will get me accurate enough.

When you add in the fact most mass produces scopes simply aren't engineered well enough to get much closer it seems mad to overspend on collimation tools. Off the shelf scopes usually have sloppy focusers, sometimes no Focuser alignment adjustment, rough secondary alignment adjusters and on top of that the tube walls are tin foil which allows the scope to flex.

Ulimately a star test is the decider and I'd consider any tool that can get me close to perfect for star testing is good enough.

[sixela]

Ulimately a star test is the decider

Then you only need a BlackCat Cheshire, because that is functionally equivalent . Seriously, there are other aspects of collimation that you can't check with a star test (secondary placement and whether the focal plane is tilted).

Fortunately, they're usually not that critical for visual observation, at least unless you plan to stick a Paracorr in the focuser or do astrophotography.

[Moonshane]

Sixella, I am interested in your comments about collimation tools and Paracorrs as I may get one of these eventually if I get a faster larger mirror than I currently have. Can you explain what you mean please?

[Doc]

At the end of the day you only buy to the spec of your scope normally. If you only have a bog standard Skywatcher dob maybe worth £200, even a hotech becomes a luxury. To buy a catseye system which costs more then the scope IMO is pointless.

For a beginnner like yourself, I would learn the art of collimation with a collicap and a cheshire, when confident and find yourself wanting more, I would go for the Hotech as it's the best laser collimator for a reasonable sum before moving into the big boys league of collimators such as Cats eye, Kendrick, and Howie.

[cotterless45]

Somewhere I lost the details of a review which suggested that there was little benefit in having a centred collimator as when you insert your eyepiece it won't be centred.

I use a cheap collimator and then check with a cheshire. I don't beleive that paying shedloads will bring so much more benefit.

As for finders, I use a Telrad with a 50p sheet of foam pad to keep the dew off.It's easy to find fuzzies especially with the telrad charts.

[sixela]

Sixella, I am interested in your comments about collimation tools and Paracorrs as I may get one of these eventually if I get a faster larger mirror than I currently have. Can you explain what you mean please?

Short version:

if you don't have a Paracorr and just observe visually, you care primarily about the proper tilt of the primary (what you set with a Cheshire), and the tilt of the secondary (what you set with a sight tube's cross hairs) is less important.

If you have a Paracorr, that changes, because if the optical axis is well aimed to the middle of the focuser but enters the Paracorr at an angle, ithe Paracorr won't work as well. So the precision of the tool that you use to set the tilt of the secondary becomes more important.

If you are an astrophotographer, the proper tilt of the secondary is also important for other reasons.

----

Technical version (ignore if you feel you don't want the hairy details):

If you don't have a Paracorr and are a strictly visual observer, it's not that important to point the reflected focuser axis correctly. If you don't, then a Cheshire (placed ideally) will still make the optical axis cross the focuser axis at the focal plane, and that's what gives you a clean star test and good high power images.

What the residual error will mean is simply that, as the focuser axis and optical axis are going to cross at an angle, the focal plane is tilted, so you have slight defocus on some parts of the edge (in one direction for one part and the other for the opposite part). But for visual observation that's not really relevant because the eye can accommodate to focus at different distances, so you're only going to see it if it's very severe, and only in the widest field eyepieces.

A second irritant is that severe errors in where the reflected focuser axis points to also mean that a Cheshire which is not placed close to the focal plane won't make you collimate the scope correctly (i.e. if you rack the focuser in and out the Cheshire reading changes, and it's only correct with the focal plane in the middle between the tool pupil and the Cheshire ring). But usually, you also know more or less where the focal plane is, so if you know that you have to place a Cheshire there, it's also not a really large issue.

If you have a Paracorr, then it's more important for you to make sure the reflected focuser axis points to the centre of the primary, to avoid a tilted focal plane. If you have a tilted focal plane, the Paracorr will actually correct coma in the slightly wrong place and add some aberrations: it really expects the on-axis object light bundle to enter centred over the Paracorr entry lens.

So you need to be more precise in tilting the secondary, and it's harder to do that with a sight tube because you can't really focus on the cross-hairs and the centre spot reflection at the same time very well.

So either a Cheshire+autocollimator or Cheshire+good laser collimator is a good idea if you're planning a Paracorr.

The former is actually more precise but interpreting the autocollimator images is quite an art form and there are some subtle traps (especially if you don't alternate with a Cheshire and use that as a final judge!); it also takes the patience of a monk.

The latter is also very precise (much more than a sight tube) if the laser collimator is very good, a lot more intuitive and faster.

If you use photography, any coma corrector (Paracorr, MPCC, Lumicon,...) suffers from the same issue as the Paracorr and even if you don't use a coma corrector, you can't stand focal plane tilt at all (it's a worse error than having some coma on axis for imaging with a DSLR!)

[sixela]

Somewhere I lost the details of a review which suggested that there was little benefit in having a centred collimator as when you insert your eyepiece it won't be centred.

The thing is that you really don't care about centring, at least not directly. Translation in the draw tube is not a problem, because even in an f/4.5, the relatively coma free field is 1.8mm wide, so an error of 0.05mm is really not going to make a difference.

Tilt is a nastier issue and of course a sloppy laser collimator will tilt and wobble. But that's something you can fix with:

-precise machining so that there is not a lot of slop,

-a longer sleeve (the longer the sleeve, the less a given difference in diameter will result in tilt)

-with a wide and accurate shoulder so that you can register the shoulder of the tool with that of the draw tube while you fasten the tool.

In some focusers, the self centring adapter will actually centre the tool but not control the real problem well, i.e. possible tilt; I've experienced that with a HoTech myself. The elastic contact of the rubber isn't as rigid as a well machined tool's long barrel or its shoulder.

I use a cheap collimator and then check with a cheshire. I don't beleive that paying shedloads will bring so much more benefit.

Usually, it doesn't. That's why I mentioned the LightPipe (not much more than other combo tools but more precisely machined and easier to illuminate).

But then the original poster asked for the best tools. And "best" is something else than "certainly good enough for all practical purposes" .

[Beulah]

This is a personal opnion only - get a Cheshire Collimator, they are cheap, reliable and ultimately the simplest and most accurate method.

If you go for a laser either buy the very best, ie the Hotech or expect aggro.

Others will argue that lasers are cool but my perception (and its is only perception) is that more questions are asked by newbies who get stuck with lasers and have problems than other methods.

Dont develope collimation paranoia also known as telescope hypochondria

Thats my two penneth on the subject.

This is spot on. When I started star gazing, a Cheshire was the way to go - very simple.

I still use mine, never been tempted to go laser...

Collimation - Cheshire Collimating Eyepiece

[Steve]

My guess is the more they cost the better or am i wrong going on that cheap = nasty, expensive is good.?

Generally, you can't go wrong with a Cheshire Collimating eyepiece, they affordable and accurate. That said, the lasers are popular because they are easier to use and more convenient, particularly if you have a long Newtonian and short arms! With lasers the cheap and cheerful are best avoided as they are often themselves out of collimation. Some dealers will try to convince you that re-aligning the laser at home is perfectly normal. It isn't! If you have bought a laser and it is not correctly aligned, return it.

HTH

[Moonshane]

If you don't have a Paracorr and are a strictly visual observer, it's not that important to point the reflected focuser axis correctly. If you don't, then a Cheshire (placed ideally) will still make the optical axis cross the focuser axis at the focal plane, and that's what gives you a clean star test and good high power images.

What the residual error will mean is simply that, as the focuser axis and optical axis are going to cross at an angle, the focal plane is tilted, so you have slight defocus on some parts of the edge (in one direction for one part and the other for the opposite part). But for visual observation that's not really relevant because the eye can accommodate to focus at different distances, so you're only going to see it if it's very severe, and only in the widest field eyepieces.

A second irritant is that severe errors in where the reflected focuser axis points to also mean that a Cheshire which is not placed close to the focal plane won't make you collimate the scope correctly (i.e. if you rack the focuser in and out the Cheshire reading changes, and it's only correct with the focal plane in the middle between the tool pupil and the Cheshire ring). But usually, you also know more or less where the focal plane is, so if you know that you have to place a Cheshire there, it's also not a really large issue.

If you have a Paracorr, then it's more important for you to make sure the reflected focuser axis points to the centre of the primary, to avoid a tilted focal plane. If you have a tilted focal plane, the Paracorr will actually correct coma in the slightly wrong place and add some aberrations: it really expects the on-axis object light bundle to enter centred over the Paracorr entry lens.

So you need to be more precise in tilting the secondary, and it's harder to do that with a sight tube because you can't really focus on the cross-hairs and the centre spot reflection at the same time very well.

So either a Cheshire+autocollimator or Cheshire+good laser collimator is a good idea if you're planning a Paracorr.

The former is actually more precise but interpreting the autocollimator images is quite an art form and there are some subtle traps (especially if you don't alternate with a Cheshire and use that as a final judge!); it also takes the patience of a monk.

The latter is also very precise (much more than a sight tube) if the laser collimator is very good, a lot more intuitive and faster.

If you use photography, any coma corrector (Paracorr, MPCC, Lumicon,...) suffers from the same issue as the Paracorr and even if you don't use a coma corrector, you can't stand focal plane tilt at all (it's a worse error than having some coma on axis for imaging with a DSLR!)

great stuff Sixella - thanks. I get it now.

personally, I use a home made collimation cap / sight tube for the secondary and once everything is concentric (major adjustments not usually needed if any) then I use a cheap plastic Cheshire with no cross hairs which seems to get collimation pretty smack on as far as my eyes tell me anyway and I suppose that's what matters for visual by definition!

I do have a 'proper' Cheshire and have had a laser but prefer the simplest of tools.

I think like anything else, you find your own method which works for you and try to perfect it.

I like the look of the light-tube.

[Tim]

another newbie question.. which is considered to be the best easiest and most accurate to use of all collimators available esp for a newbie like myself.

regards.Rob

A laser is certainly the easiest, very intuitive, can be used in the dark, and will give you pretty good collimation in about 2 mins flat.

A Chesire eyepiece will give you a bit more accuracy, but is not quite so intuitive.

Dont forget the good old star test too!

If you are anywhere near Coventry, you are welcome to pop over and have a look at these items, and see which would suit you best. You can practice on one of my newts with pleasure Just drop me a PM if you want.

Cheers

Tim

[TheThing]

Good grief did this thread go off topic or what? I think we could safely cut out all the posts between Astro_Baby's and TJ's.

I'm going to be subtle here but can we try and keep on topic and just answer the query asked in all future posts please?

If you really need to pontificate, start your own thread!

[sixela]

great stuff Sixella - thanks. I get it now.

personally, I use a home made collimation cap / sight tube for the secondary and once everything is concentric (major adjustments not usually needed if any) then I use a cheap plastic Cheshire with no cross hairs which seems to get collimation pretty smack on as far as my eyes tell me anyway and I suppose that's what matters for visual by definition!

Yup, that is a perfectly valid view (as you can also read from one of the above posts). For visual observation, the most important thing to tweak (the tilt of the primary mirror) can be evaluated with a €3 collimation cap or a Cheshire.

[sixela]

... [Never mind; off topic]

[TheThing]

it's a rhetoric question.

[Alfa Omega]

thanks to each and everyone of you people who responded all your points have been taken onboard and i will now give it a lot of thought before i make up my mind which to go for . thanks again all much obliged.

regards.Rob