Cheshire collimator

[tripleped]

I found a meoptex Cheshire collimator (short version) 5 star rated on amazon. Anyone have thoughts / recommendations on a specific Cheshire? Does the brand really matter? Appreciate any advice on this. 

[bomberbaz]

As long as it is correctly collimated itself and isn't sloppy in the focuser draw tube then I would have thought it should be fine. Happy to be corrected. 

I can't find the one you mention available on amazon but FLO sell a basic but perfecftly suitable option. https://www.firstlightoptics.com/other-collimation-tools/astro-essentials-cheshire-collimating-eyepiece.html

 

 

[AlexK]

This one I guess: https://www.amazon.com/MEOPTEX-1-25Inch-Collimating-Cheshire-Eyepiece/dp/B07KF191VL 

Looks the same as that FLO.

IMO. You can find a laser collimator for that price. And don't buy their "sighting tube" ad. As a sighting tube supposed to be individual for a particular aperture.

[MrFreeze]

I had absolutely no joy with the short cheshires - can't focus on the crosshairs at all. I ended up with one of the longer ones through Aliexpress. https://www.aliexpress.com/item/33056951646.html?spm=a2g0o.productlist.0.0.44072659Zj8JPx&algo_pvid=076441e5-a541-42ea-bcf3-a42cdf830ed6&algo_expid=076441e5-a541-42ea-bcf3-a42cdf830ed6-2&btsid=2100bde116045638319288156edc55&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ Not bad at all for less than a tenner, and only 9 days shipping.

David

[Matt61]

I'd say a Cheshire is far more use than a laser which is out of collimation. It's only natural to assume a laser is the bees knees. ( not if the beam isn't accurate)

[bomberbaz]

54 minutes ago, Matt61 said:

I'd say a Cheshire is far more use than a laser which is out of collimation. It's only natural to assume a laser is the bees knees. ( not if the beam isn't accurate)

I had to recollimate my laser recently, it is a fiddly job and best done with a lathe

[wookie1965]

I only used a short Cheshire for my 200p and the collimation was spot on. 

[Matt61]

Same for my 150P. It came second hand with laser . I only got collimation right when I got the Cheshire. 

[AlexK]

A laser collimator (LC) collimation doesn't need a lathe at all. If you get this super cheap one on Ali: https://www.aliexpress.com/item/4000184670320.html you will also get the 2" to 1.25" adapter with it. Just clamp that adapter to something (no vises or C-clamp? Get a pile of heavy books around it). Project to the distant wall (5 meters - bare minimum), tape a piece of drafting paper under the beam. Mark the beam position. Then rotate its 1.25" body in the 2" adapter a bit and mark the spot again. Finally, find the center of the resulting circle, and then collimate with screws to hit it. Repeat if in doubt. I do the same using my stock Zhumell 2" to 1.25" eyepiece adapter.

But if you have a standard ring or dot center marker on your primary and a 2x Barlow, then better yet, you can adopt the simplified barlowed laser collimation technique, which makes the precise collimation rivaling even the expensive autocollimator device a nobrainer:

1. Use the LC as normal (get the laser return dot disappear in its bullseye target's hole by moving the primary).
2. Now put your Barlow into the focuser and then the LC into it.
3. Look to the primary from the front and wiggle the laser collimator until the center marker is well lit with the cone of the laser light (you should see edges of the marker well).
4. Look at the bullseye screen of the LC and locate the shadow of the mirror marker (you may need to play with primary a bit, as the marker shadow/image is zoomed 2x+).
5. Adjust the primary to perfectly center the shadow around the hole (pay attention to its ellipticity, as the bullseye screen is at 45 degrees.

With experience you will just skip #1, so no LC collimation is ever needed as soon as the wide cone of the laser light can cover the target on the mirror entirely (you should be able to see its edges so the return beam produces a recognizable shadow on the bullseye). Another typical flaw of cheap LCs the non-circular laser dot will be even beneficial with this method as it's making the barlowed spot even larger .

Edited November 5, 2020 by AlexK