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Which Collimation tools?

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#1 Kevin_91

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Posted 12 November 2011 - 03:05 PM

Which tools do you use? Do you use multiple? Which works best?

I need to pick a tool out for my 130mm Newt, and i'm sort of confused. Most the guides tell you to use 2-3 tools, is that a must? It seems like it would cost more to collimate a cheap newt then to actually buy one!

Is there a way to do a good collimation with a single tool? I assume the more expensive Laser is more effective? How do you go about collimating?

#2 C_Moon

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Posted 12 November 2011 - 06:53 PM

What is the focal ratio of your scope? Do you have a collimation cap?

#3 Ed Wiley

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Posted 12 November 2011 - 07:38 PM

Congratulations you have a scope and you know you need to collimate it. You are on first base.

See:
http://www.skyandtel...iy/3306876.html

Its a fairly good primer for collimating.

Suggested: From ScopeStuff, get a Cheshire

1.25" Cheshire Collimator with Cross Hair Sight Tube
for Newts and Dobs

Alternative: If you are a member of a club or there is a club in your town, join and let experienced members help you.

Ed

#4 Achernar

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Posted 12 November 2011 - 08:58 PM

If you have a Newtonian with a focal ratio of 6 or above you can collimate it just fine with a sight tube. It has crosshairs that facilitate collimation and help you determine if everything is concentric with each other when looking through the sight tube. If you have one faster than that, then a Cheshire eyepiece is used afer using a sight tube to get the diagonal aligned with the focuser if and when that is required. Most of the time, you'll just need to use a Cheshire eyepiece to check the collimation of the primary mirror unless your telescope has been through a bumpy ride or been disassembled for washing the optics. It projects a donut of light on the mirror and using the center spot on the mirror, you align the primary mirror after using the sight tube to line up the secondary mirror with respect to the focuser. After getting the outline of the primary mirror and secondary mirrors concentric withn each other by adjusting the tilt of the diagonal, the sight tube is useful again when it's time to adjust the primary mirror until the reflection of the diagonal mirror is centered in the outline of the primary mirror and everything looks like the scoring rings of a bullseye target. A quick check on a star should at that point show your telescope is collimated and ready to give you the best possible views the seeing conditions and the optics themselves allow.

Laser collimators can work very well, but with a big caveat. They must themselves be collimated, otherwise you will mis-collimate your telescope. It's the same sort of problem that led to the Hubble Space Telescope being launched with a serious problem with spherical abberation because the laser interferometer used to test the mirror was set up incorrectly. Good ones do not come cheap, cheap ones are a waste of money and time. Get a good sight tube or Cheshire-sight tube combination tool. Of if you are really handy, make your own.

Otherwise, Orion and other vendors can supply you with collimation tools that will get your telescope collimated correctly and keep it that way.

As for me I use a set of collimation tools made by Tectron, which consists of a sight tube, a Cheshire eyepiece and an autocollimator for even finer tweaking of my collimation. I just use the sight tube on my 6-inch F/8 Dob because for slower Newtonian a sight tube is sufficient. When collimating my 10 and 15-inch Dobs I use the sight tube only when the secondary is cleary out of whack, most collimation only requires minor tweaks to the primary mirror which is done in a couple of minutes with the Cheshire eyepiece. I can use it even in the dark when I shine a flashlight into the opening on the collimation tool. The primary mirrors in these telescopes have a F/4.5 focal ratio, and hence they have center spots for collimation. All told I bought the set at the Okie-Tex starparty for less than $100.00 from noen other than Rick Singmaster, who makes some incredibly good telescopes with which I was highly impressed.

Taras

#5 UmaDog

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Posted 12 November 2011 - 09:04 PM

Perhaps these links will help? http://www.physiol.o...tionLinks.shtml

#6 C_Moon

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Posted 12 November 2011 - 11:00 PM

Which tools do you use? Do you use multiple? Which works best?

I need to pick a tool out for my 130mm Newt, and i'm sort of confused. Most the guides tell you to use 2-3 tools, is that a must? It seems like it would cost more to collimate a cheap newt then to actually buy one!

Is there a way to do a good collimation with a single tool? I assume the more expensive Laser is more effective? How do you go about collimating?


Gary Seronik (S&T) has an excellent article that he recently posted in his blog on this very topic.

I almost exclusively use the collimation cap that came with my scope to collimate. I also have an Orion collimating eyepiece (combination cheshire/sight tube) that I use to adjust the secondary, but I rarely need to do that.

I'll add that I go many months without having to do any adjustments whatsoever. When I do need an adjustment, typically it is a very small adjustment of the primary mirror. For the record, I do travel with my scope at least 1/month (usually more than that).

One other Seronik article that was very influential to me discussed secondary alignment and it ran in the July 2011 issue of Sky and Telescope.

#7 Kevin_91

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Posted 13 November 2011 - 02:24 AM

Thanks for the help all! My newt is an f/5, and i don't really see myself getting one much slower than f/6 in the future. So it appears a Cheshire eyepiece will be the best? My current FL is 650, I have a 6" I just recieved with a 735mm FL, and then I plan on upgrading to a possible 10" with a 1200 FL within the next 6 months. I assume the cheshire should be fine for all right?

#8 Achernar

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Posted 13 November 2011 - 08:53 AM

You'll definitely need a sight tube or collimation cap plus a Cheshire eyepiece, or simply buy a combination sight tube and Cheshire eyepiece collimation tool. Once you get everything collimated the first time, all you should have to do is check the primary mirror with the Cheshire eyepiece before each observing session. Collimation is very critical at F/5 and below, and it's not unusual for it to wander a little over time. What you should not have to do is align everything each time you use the telescope, that indicates something's loose or broken. Since you have a solid tube, it should behave like my 6 and 10-inch dobs, the collimation only rarely needs to be adjusted slightly.

Taras

#9 howard929

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Posted 13 November 2011 - 09:12 AM

From my short experience with this hobby a barlowed laser works just fine at f/6 and from what I've read here at CN that method works equally well at f/5. One big + with that method is I can check collimation in the dark after I set-up.

Howard

#10 Ed Wiley

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Posted 13 November 2011 - 10:22 AM

I suggested the Cheshire because you did not want to spend more on collimation equipment than you spent on your scope. The Cheshire/cap combination will work on any sized scope you are likely to buy. I use the Glatter Blug barlowed laser system, but that sets you back some cash. IMO the laser alone does not work well, but the barlowed laser system is fast and easy. On the other hand, the humble Cheshire works just as well. I use the Glatter system because it is easier to do a one-person collimation on my 12.5" dob.

Ed

#11 Feidb

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Posted 13 November 2011 - 10:31 AM

I've used a $3 plastic cap since the mid 90's and it has worked like a charm. Granted, I've been at this a long time, but still... I wasted $79 on a laser and it stinks. I only use it in a pinch. I've borrowed Cheshire tube. I've even borrowed and used a Blug. I still go back to my $3 plastic reflective cap. Just sayin'...

#12 UmaDog

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Posted 13 November 2011 - 10:43 AM

Aren't a Cheshire and a collimation cap the same thing? I keep seeing them referred to as different things, but surely they're not because the Catseye Blackat is referred to as a Cheshire, and it's basically just a well-machined collimation cap. Farpoint also make something similar: www.buytelescopes.com/Products/13430-Farpoint-Astro.aspx

The Cheshire/sight-tube is obviously a different thing.

#13 maakhand

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Posted 13 November 2011 - 10:47 AM

collimation is something that gets easier everytime you do it. i personally prefer passive tools ie. sight tube and cheshire etc. Taras's two posts already explained everything that needs to be said. as you need a sight tube for secondary anyway a combo tool ( cheshire and sight tube in a single tool) seems logical and economical. as your current scope has a 1.25" focuser, a 1.25" combo tool will serve you perfectly. in future when you get those bigger scopes it will still be usable for it. by that time you will be comfortable with collimation enough to decide for yourself whether you need more precision that an additional autocollimator provides or a set of 2" quality tools :D.

#14 howard929

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Posted 13 November 2011 - 11:02 AM

I've used a $3 plastic cap since the mid 90's and it has worked like a charm. Granted, I've been at this a long time, but still... I wasted $79 on a laser and it stinks. I only use it in a pinch. I've borrowed Cheshire tube. I've even borrowed and used a Blug. I still go back to my $3 plastic reflective cap. Just sayin'...


I bought one of those from A-line for just a couple of bucks and I'm starting to believe that collimation is a trust thing more then anything else. With experience and trust that you're doing it all the right way, a collimation cap is essentially as good as any other method provided there's a light source to see by.

Howard

#15 GeneT

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Posted 13 November 2011 - 02:54 PM

I use two, and highly recommend them both: 1) Howie Glatter Laser with TuBlug; 2) a CatsEye collimation system. Both are excellent. Both are well made and should last a life time. If you can only afford one, I would get the Glatter system. There are less expensive options available that might meet your needs.

#16 Connor Walls

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Posted 13 November 2011 - 03:06 PM

I just use the collimation cap that came with my scope. Sure, it may not be as precise as a laser collimator, but it gets the job done.

#17 simpleisbetter

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Posted 13 November 2011 - 04:39 PM

For primary alignment the collimation cap can do a surprisingly good job. Add a sight tube to aid in secondary centering and alignment. Those two will get you pretty good collimation, as good as all but the expensive $150+ lasers or Cats Eye passive tools. For really accurate collimation, all you need to add is an autocollimator.

You really don't need to spend a lot for the basic tools to collimate your scope well. A good source to get you started is AstroSystems. You can get the lightpipe/autocollimator combo for $80.

#18 Feidb

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Posted 13 November 2011 - 04:47 PM

I must emphasize that there must be plenty of light for the plastic cap to work, otherwise it is useless. If you arrive at the observing site after dark, you'll need something else. That is where I am forced to use the laser, which only gets me in the ballpark. I then have to tweak the mirror using bright stars. Then again, it depends on the night as to whether I do much tweaking. I don't do much planetary work or bother with double stars, yet I want enough precision to get a decent image at 220X to 390X if conditions allow. I don't observe above those magnifications, just not my thing (except for a goof or an experiment) (I normally observe at 101X to 131X). If the conditions don't allow, a rough alignment will do.

On a normal night, regardless of conditions, my plastic cap gets me where I want and I rarely have to tweak unless the mirror shifts. I have accidentally knocked into the OTA before. If I plan on any planetary work, I spend a bit more time and will tweak the mirror on a bright star at high power, but this is rare as the cap usually gets me close enough. More than likely, air currents or atmospheric turbulence will be more of a problem than any slight misalignment.

#19 artao

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Posted 13 November 2011 - 05:56 PM

SimpleIsBetter already mentioned AstroSystems LightPipe collimation tool. I have to +1000 that!! It's currently the only tool I have, and I LOVE it. In the dark, you can shine a dim red light on the plastic ring, and you get easy full illumination of the alignment circle. VERY nice tool. I DO want to pick up an autocollimator as well tho, for fine tweaking.

EDIT: Oh! Here's a linky to the AstroSystems page with the LightPipe and autocollimator :: http://www.astrosyst...iz/coltlsm1.htm

#20 spaceoddity

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Posted 14 November 2011 - 01:17 AM

At the very least you'll want to check primary collimation each time you're out(primary is by far the most important). The collimation cap and the cheshire both work well for this, and no they are not exactly the same thing(cheshire has crosshairs). However neither is particualarly good at sceondary alignment and tilt. The sight tube is for centering the secondary mirror under the focuser and this is something that usually only needs to be done once. It can be achieved fairly accurately just eyeballing it down the focuser tube if you don't have a sight tube. A good laser collimator makes scondary tilt a snap and when barlowed is very accurate(and easy) for primary alignment also.

#21 UmaDog

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Posted 14 November 2011 - 09:28 AM

and no they are not exactly the same thing(cheshire has crosshairs).

But isn't that why it's called a Cheshire/sight-tube combination tool? The cross hairs are the sight-tube portion. The Catseye blackcat is labelled as a Cheshire and that has no cross-hairs. Same with the Farpoint. As I say, both of those are simply well-machined collimation caps. Ergo the collimation cap is a Cheshire, no? I'm not trying to be argumentative, it's just that the collimation cap is often treated as some different class of tool when in fact it must be a Cheshire. That's probably confusing to beginners.

EDIT:
I checked with Jim Fly at Catseye. Basically, a Cheshire is defined as a tool for measuring primary axial error using a peep-hole drilled into a white or reflective (but not mirror) surface. There are a few variants. A cap has the whole surface being reflective. The 45 degree cut-out design which a lot of combo tools has is another variant. The Catseye tools have a reflective ring which is sized to correspond with the Catseye centre spot and so make alignment more accurate. The cross-hairs are an addition to the Cheshire and make it a combo tool which can also be used to adjust the primary.

#22 UmaDog

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Posted 14 November 2011 - 09:29 AM

Catseye sell a red LED that clips onto the spider and allows use of passive tools in the dark.

#23 shawnhar

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Posted 14 November 2011 - 01:01 PM

and no they are not exactly the same thing(cheshire has crosshairs).

But isn't that why it's called a Cheshire/sight-tube combination tool? The cross hairs are the sight-tube portion. The Catseye blackcat is labelled as a Cheshire and that has no cross-hairs. Same with the Farpoint. As I say, both of those are simply well-machined collimation caps. Ergo the collimation cap is a Cheshire, no? I'm not trying to be argumentative, it's just that the collimation cap is often treated as some different class of tool when in fact it must be a Cheshire. That's probably confusing to beginners.

From what I understand a cheshire has a reflective ring, collimation cap does not. I glued a shiny washer inside my collimation cap and turned it into a cheshire.

I use a 1.25" Combination Cheshire with Cross Hair Sight Tube tool.
I think it is an Orion, "Newtonian Collimation Tool" and I seriously doubt anyone could use a fancy expensive tool(s) and make any visual difference at my eyepiece.

#24 Vic Menard

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Posted 14 November 2011 - 03:01 PM

...From what I understand a cheshire has a reflective ring, collimation cap does not. I glued a shiny washer inside my collimation cap and turned it into a cheshire.

The original Cheshire eyepiece was designed by F. J. Cheshire in 1921. B. L. Souther brought this tool to the amateur astronomy community in a 1968, Sky & Telescope, Gleanings for ATMs article. The tool described by B. L. Souther was a simple windowed collimator with a 45-degree polished surface (no cross hairs) and a peep sight.

The simple centering tool, or "peep sight", has no reflective surface and is designed to simply center the user's pupil in the focuser drawtube. It was not intended to be used with a primary mirror center spot (although, if the reflection of the peep sight pupil is visible, and the center spot can be seen against the dark background, it could be used as a makeshift Cheshire collimator).

Today, most collimation caps either have the surface facing the primary mirror painted white or have a reflective material affixed to the inner surface so the collimation cap pupil and the primary mirror center spot can both be seen against the bright background. Since the pupil, or the bright ring around the pupil, is used to align the primary mirror center spot, these tools work identically to (and are subject to the same potential weaknesses) as the original Cheshire eyepiece.

A sight tube is a longer tube with cross hairs at one end of the tube and a peep sight at the other end of the tube. Sight tubes and simple peep sights were in regular use long before Cheshire eyepieces or collimation caps became commonplace.

Combo tools like the AstroSystems LightPipe or the CatsEye TeleCat combine a sight tube and a Cheshire eyepiece in one tool.

I use a 1.25" Combination Cheshire with Cross Hair Sight Tube tool.
I think it is an Orion, "Newtonian Collimation Tool" and I seriously doubt anyone could use a fancy expensive tool(s) and make any visual difference at my eyepiece.

Used properly, the combo tool is a very capable alignment tool. If I had only one tool to use, it would be my choice too. But there are valid reasons to use those "fancy expensive tools" you find no need for.

#25 UmaDog

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Posted 14 November 2011 - 03:18 PM

Interesting, thanks, I always wondered who Cheshire was.






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