Telescope Reviews: Center marks

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Equipment Discussions >> Reflectors

Pages: 1

tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Center marks
#5535627 - 11/23/12 02:24 PM

OK, We have "hot spot", triangles and donuts. What is the advantage of each and what do I want? I use a simple laser, am trying to learn Barlowed laser and also have a Chelshire eyepiece. Educate me, please.

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DavidC
Pooh-Bah

Reged: 11/24/05

Loc: Mesa, Arizona

Re: Center marks new

new

[Re: tag1260]
#5535753 - 11/23/12 03:39 PM

I like the center ring or doughnut because I can center my laser beam right in the center of the doughnut to adjust my secondary. For the adjustment of the primary, I see the doughnut's reflection in the combination cheshire / sight tube. Im not really sure about using the triangle mark.
David

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Jeff Porter
super member

Reged: 09/03/10

Loc: Utah

Re: Center marks new

new

[Re: tag1260]
#5535758 - 11/23/12 03:42 PM

The difference of the shape of the center spots is a matter of personal preference when using a Cheshire for aligning the primary mirror only. A Cheshire will frame the triangle, hot spot, or doughnut. With a triangle the tips will just touch the inside of the Cheshire circle, and the hotspot will fill the Cheshire circle. The centering triangle and hotspot I purchased from Jim Fly at CatsEye fit perfectly into the circle of my 1.25" and 2" cheshires. I recommend a triangle or hotspot if you are using a Cheshire since they make it easy to determine the final adjustments.

The shape of the center mark makes no difference when using the laser/Barlow method of aligning your mirrors. The only thing that matters here is that the laser itself is properly aligned and that the center spot have a hole to reflect a return beam. Use just the laser for setting the secondary mirror, and attach the Barlow before centering the return image when setting the primary. I have a Glatter TuBlug that is perfect for setting the primary mirror using this method.

As with any collimation it is good to do a quick star test for verification.

-Jeff P

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DavidC
Pooh-Bah

Reged: 11/24/05

Loc: Mesa, Arizona

Re: Center marks new

new

[Re: tag1260]
#5535766 - 11/23/12 03:47 PM

Using the barlowed method, the reflection of the doughnut on the primary shows up on the pattern on your barlow. You'll have a red diffused light pattern and the whiteish reflection of the center mark will show in the middle. You adjust the primary untill that o-ring is centered in the center.
David

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tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Re: Center marks new

new

[Re: tag1260]
#5535836 - 11/23/12 04:30 PM

Where can you buy a simple center spot (donut). I would prefer NOT to use a binder ring for paper.

Thanks
Tag

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sslcm56
member

Reged: 07/20/12

Loc: Montgomery, Al.

Re: Center marks new

new

[Re: tag1260]
#5536703 - 11/24/12 07:09 AM

Is it the same as a bought barlowed laser if I use the barlow and laser that came with the scope? I have been thinking about a Catseye system.

Edited by sslcm56 (11/24/12 07:10 AM)

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FirstSight
Postmaster

Reged: 12/26/05

Loc: Raleigh, NC

Re: Center marks new

new

[Re: sslcm56]
#5537075 - 11/24/12 11:21 AM

The triangle or hotspot is clearly superior to the donut IF you're using the Catseye cheshire or autocollimator, but is actually mildly counterproductive when using the Glatter TuBlug. The reason is that the Catseye triangle projects a variably distorted (bowed rather than straight) image of the triangle edges onto the Tublug screen, making it more difficult to tell when the triangle is properly centered.

That said, no matter how close (but still imperfect) or how badly out of collimation a scope is when you start, collimation life is easier and sweeter for those possessing both the Catseye and Glatter sets of tools. IMHO the advantages of the triangular spots to the Catseye tools are significant enough to outweight the disadvantage to the Glatter set, because the Glatter set is best for quickly achieving approximately close collimation, the Catseye set for either refining it to precise spot-on collimation or else for intially setting up the secondary properly underneath the focuser (which latter task you only need to do initially and rarely after that).

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tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Re: Center marks new

new

[Re: FirstSight]
#5537138 - 11/24/12 12:01 PM

According to Catseye (I sent them an email) the Hot Spot isn't quite as good if you don't use their collimating tools and use a Chelshire. The triangle is a better choice to use with a Chelshire eyepiece. Looks like I'll be using the triangle on mine, at least until I can afford a set of Catseyes..

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Atl
sage

Reged: 04/13/12

Re: Center marks new

new

[Re: FirstSight]
#5537139 - 11/24/12 12:01 PM

A plain square piece of electrical tape worked for me, but I am not using a laser...I use a cheshire and a collimation cap.

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dan777
professor emeritus

Reged: 11/16/07

Loc: Indiana

Re: Center marks new

new

[Re: Atl]
#5537367 - 11/24/12 03:10 PM

I prefer the donut over the triangle. It gives a sharper and higher contrast image when using my cheshire or collimation cap. This is due to two reasons: the hole in the donut is slightly larger than the hole in the triangle and the white donut vs red triangle color.

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles

Re: Center marks new

new

[Re: dan777]
#5537445 - 11/24/12 03:59 PM

Terminology refresher:
1. Collimation cap (A simple peep-hole, though not good enough for scopes below f/10. I don’t recommend these except, perhaps, as a quick check to see if the optical elements are at least in gross alignment at the start).
2. Laser collimator (not useful unless perfectly collimated itself, possessed of a small beam diameter, and not accurate enough for primary mirror collimation unless used with a Barlow lens, but quite useful in the dark.
3. Sight Tube (Cylinder with peep hole at one end and crosshairs at the other. Combination tools contain this tool).
4. Cheshire (Cylinder with interior annular reflective surface and blackened center area, producing a reflection from the primary mirror that appears as a bright ring with a dark center. Combination tools contain this tool).
5. Autocollimator (Cylinder with a reflective mirror inside the peep-hole cap. The internal mirror is perpendicular to the optical axis of the focuser. It produces multiple reflections of the primary mirror’s center marking).
6. Combination Sight Tube/Cheshire (least expensive, but a little harder to use. It combines the crosshairs of the sight tube and the reflective interior surface of the Cheshire. There are many inexpensive models in the market, and a couple better ones).

So, one does not collimate a scope with a cheshire and a collimation cap. Both are tools to aid in alignment of the Primary Axis, not Secondary (Focuser). Atl was probably referring to a #6 above when he said Cheshire. It is a common error--even on the part of some manufacturers.

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tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Re: Center marks new

new

[Re: Starman1]
#5538132 - 11/25/12 12:59 AM

Thanks for the replies.
Is anyone using Hot Spots or Triangles and NOT using CatsEye collimation tools? How do they work with a Laser or Barlowed laser?

On another note, Is everyone who is using donuts using binder reinforcement rings? Does the glue hold up to condensation?

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beatlejuice
scholastic sledgehammer

Reged: 04/05/11

Loc: Hamilton, ON,Canada

Re: Center marks new

new

[Re: tag1260]
#5538157 - 11/25/12 01:26 AM

Quote:

On another note, Is everyone who is using donuts using binder reinforcement rings? Does the glue hold up to condensation?

Yes, and the glue holds up fine for me and if it ever came loose the remaining residue would make respotting easy.

Eric

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Jason D
Postmaster

Reged: 10/21/06

Loc: California

Re: Center marks new

new

[Re: tag1260]
#5538201 - 11/25/12 02:07 AM

Quote:

Is anyone using Hot Spots or Triangles and NOT using CatsEye collimation tools? How do they work with a Laser or Barlowed laser?

With Glatter TuBlug, the Hotspot works great if you apply a template.

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tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Re: Center marks new

new

[Re: Jason D]
#5538710 - 11/25/12 01:02 PM

Thanks for the pics. I see it works great.

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Mike E.
Carpal Tunnel

Reged: 01/26/10

Loc: Moonstone Observatory

Re: Center marks new

new

[Re: tag1260]
#5538985 - 11/25/12 03:41 PM

Quote:

Where can you buy a simple center spot (donut). I would prefer NOT to use a binder ring for paper.

Thanks
Tag

Binder rings are also available in Plastic or Vinyl form at better Stationary stores.

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tag1260
sage

Reged: 10/07/12

Loc: Ohio, USA

Re: Center marks new

new

[Re: Mike E.]
#5539863 - 11/26/12 06:55 AM

Do you know if the glue on the vinyl ones is any better than the paper ones (as in NOT water soluble) ?

Thanks

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okieav8r
Carpal Tunnel

Reged: 03/01/09

Loc: Oklahoma!

Re: Center marks new

new

[Re: tag1260]
#5540331 - 11/26/12 01:41 PM

Quote:

Do you know if the glue on the vinyl ones is any better than the paper ones (as in NOT water soluble) ?

Thanks

If you stick one of those on your mirror, it ain't coming off until you take it off.

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Jason D
Postmaster

Reged: 10/21/06

Loc: California

Re: Center marks new

new

[Re: tag1260]
#5540365 - 11/26/12 02:01 PM

Quote:

Do you know if the glue on the vinyl ones is any better than the paper ones (as in NOT water soluble) ?

Thanks

I suggest you purchase both -- they can't be that expensive -- then try them on some glass surface.

Jason

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles

Re: Center marks new

new

[Re: Jason D]
#5540408 - 11/26/12 02:22 PM

I found some self-adhesive white reflective vinyl reinforcement rings at Staples. Not only do they stick on during cleaning (I guess unless you use alcohol), but their high reflectivity makes seeing all 4 reflections in the autocollimator much easier.

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