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What Is This Collimation Tool Called?

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#1 Orion68

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Posted 24 July 2021 - 09:41 PM

Since acquiring a 6" F5 Newt a few months back I've learned a few things about collimation thanks to the instructions provided by Vic, Don, Asbytec and others on CN. Thanks to them I now have a well-collimated scope which is a joy to use.

 

I'm still a newbie though and this will prove it. The collimation tool I used is shown here but I have no idea if this is a sight tube, a Cheshire, or something else.

 

It is quite old and I can't remember where I got it.

 

It fits in a 1.25" focuser and the ring on the bottom is reflective so it's easy to see when being used. There are no crosshairs in this device.

 

What is this thing actually called?

IMG 20210724 192725692
IMG 20210724 192733799
IMG 20210724 192714764

 



#2 AhBok

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Posted 24 July 2021 - 10:41 PM

Appears to be a Cheshire to me with the ring on the inside surface, et., al.
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#3 macdonjh

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Posted 24 July 2021 - 10:45 PM

It's a collimation cap.

+1


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#4 Keith Rivich

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Posted 24 July 2021 - 11:04 PM

We used to call these "auto-collimators". Inside the barrel is a mirror which, when placed in the focuser, creates a closed optical path if secondary is properly collimated. These are typically used in daylight. Looking into the device one should see the mirror in the cap as a dark ring. If the ring is bright the secondary is off a bit. 


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#5 telesonic

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Posted 25 July 2021 - 12:08 AM

Yes, this is a Cheshire tool - no crosshairs in the tube, the refelective ring is on the outer surface of the insert. Your particular one was/is made by CatsEye. I have the same tool in my scope kit. The inside surface near the pupil is not mirrored, so it's not really an autocollimator, I don't think.

 

 

It's a good piece, and it was designed to be used with the reflective primary spots (triangular/etc) from them. CatsEye tools will bring up the site with a simple search.

 

Cheers,
T


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#6 Orion68

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Posted 25 July 2021 - 03:10 AM

Yes, this is a Cheshire tool - no crosshairs in the tube, the refelective ring is on the outer surface of the insert. Your particular one was/is made by CatsEye. I have the same tool in my scope kit. The inside surface near the pupil is not mirrored, so it's not really an autocollimator, I don't think.

 

 

It's a good piece, and it was designed to be used with the reflective primary spots (triangular/etc) from them. CatsEye tools will bring up the site with a simple search.

 

Cheers,
T

I received a PM from another CN member and he said the same thing, it's from CatsEye. There is no mirror inside.

 

If my understanding is correct, a Cheshire is used to collimate the primary only. But, I found that it helped me to make sure the secondary mirror edge and the primary reflection in the secondary were concentric with the focuser tube.

 

Still learning about the nuances of collimating a Newt, so is there a better tool for collimating the secondary?


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#7 Orion68

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Posted 25 July 2021 - 03:13 AM

We used to call these "auto-collimators". Inside the barrel is a mirror which, when placed in the focuser, creates a closed optical path if secondary is properly collimated. These are typically used in daylight. Looking into the device one should see the mirror in the cap as a dark ring. If the ring is bright the secondary is off a bit. 

Doesn't appear to be a mirror inside.



#8 sixela

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Posted 25 July 2021 - 03:57 AM

But, I found that it helped me to make sure the secondary mirror edge and the primary reflection in the secondary were concentric with the focuser tube.

 

That's because Cheshires can also be used as collimation caps.

 

But these are less accurate for placing the secondary with respect to the focuser axis and for tilting the secondary correctly than a specific tool for it -- usually you see quite a bit of the opposite end of the tube around the secondary, and so it's not that easy to see whether the edge of the secondary and the edge of the reflection of the primary are exactly centred.

 

You can, however, already see gross errors in the tilt of the secondary if you rack the focuser in and out. If the Cheshire ring reflection and the image of the primary centre spot stay concentric over the entire travel of the focuser, then the focuser axis is indeed pointing close to the middle of the primary. If they seem to move with respect to one another, then it isn't, and then you need to do the Cheshire reading with the focal plane halfway between the pupil of the tool and the physical Cheshire ring location in the tool for the tool to still work well.

 

You have a "passive" tool for setting the tilt of the secondary, a sight tube with cross-hairs, and an "active" one, the laser collimator. With a sight tube you set the tilt of the secondary so that the primary's centre spot appears behind the cross hairs. The tricky part is that focusing the eye on both the cross hairs and the centre spot is hard (the cross hairs are close and the centre spot roughly at one focal length).

 

Laser collimators don't suffer from this and are more precise when they're good (i.e. sit well aligned with the focuser with the laser parallel to the focuser axis), but cheap ones usually aren't -- in my experience the first good one is the FarPoint laser, even though it often needs a really good 2"-1.25" adapter if you have a 1.25" laser collimator and a 2" focuser. Mind you, there are expensive ones that I don't consider reliable (the HoTech and the the Baader come to mind).

 

Once you've set secondary tilt with a sight tube or a laser collimator and set primary tilt using the Cheshire, you can also evaluate the placement of the secondary by using the Cheshire with the focuser racked out enough so that the image of the primary fills the secondary completely; if the secondary is liberally sized you might need extensions to place the Cheshire's pupil far enough. From that vantage point the image of the primary and the edge of the secondary should be concentric. If they are not completely concentric (i.e. when you rack out the focuser the primary is clipped first at one spot on the edge of the secondary) then the secondary's not ideally placed, but small errors are not that relevant (they just shift the fully illuminated field at low power a bit).

 

Once the secondary is tilted correctly (by using a sight tube with crosshairs


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#9 Starman1

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Posted 25 July 2021 - 10:38 AM

A Cheshire ep has a 45 degree cutout in the side.  If there is no mirror just below the peep hole, it's a collimation cap.  Placing a mirror with a hole in it concentric with and up against the peep hole would make it an autocollimator. No mirror, no cutout.  It's a mere collimation cap.

No, that is only one type of Cheshire.  This is the other kind, like Catseye, Farpoint.

The reflective surface on the bottom returns a reflection of a bright white circle with a dark center, i.e. a Cheshire.

It works exactly the same as the type with the 45 degree window.

Farpoint Cheshire:

https://www.optics-p...yepiece/p,16412

Catseye Cheshire:

https://www.catseyec...om/xl-bc640.jpg

 

Add crosshairs to either type and you have a combination tool.  Of course, in that case, the tube is longer.


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#10 Vic Menard

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Posted 25 July 2021 - 11:22 AM

No, that is only one type of Cheshire.  This is the other kind, like Catseye, Farpoint.

The reflective surface on the bottom returns a reflection of a bright white circle with a dark center, i.e. a Cheshire.

It works exactly the same as the type with the 45 degree window.

Farpoint Cheshire:

https://www.optics-p...yepiece/p,16412

Catseye Cheshire:

https://www.catseyec...om/xl-bc640.jpg

 

Add crosshairs to either type and you have a combination tool.  Of course, in that case, the tube is longer.

It looks quite a bit like a Catseye 1.25-inch Cheshire  https://www.catseyec...eyewnickbig.jpg  --notice the knurled top ring, small pupil, and recessed surface for the blue reflective Cheshire ring. I suspect this might be a knockoff created with a 3D printer (zooming in on the OP's image, it looks like it might have been painted blue). 

 

(Edit: Corrected to match the OP's description--thanks Don!)


Edited by Vic Menard, 25 July 2021 - 12:10 PM.

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#11 Vic Menard

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Posted 25 July 2021 - 11:41 AM

A collimation cap is usually configured as a simple press fit piece with a center pupil and a white (or other light color) underside that is used to visualize the (dark) primary mirror center mark position relative to the collimation cap pupil (like this cap with a retro reflective underside  https://agenaastro.c...t-eyepiece.html  ) Used this way, a collimation cap is a Cheshire derivative. Both are primary mirror alignment tools and both magnify any residual primary mirror error 2X.

 

Cheshire eyepieces can be used with carefully matched primary mirror center markers to enhance the alignment read precision. A "calibrated" Cheshire is configured this way.

 

A collimation cap without a reflective or light colored underside is usually referred to as a "peep sight", which is essentially a centering tool for viewing the alignment of concentric reflections. 


Edited by Vic Menard, 25 July 2021 - 11:44 AM.

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#12 Starman1

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Posted 25 July 2021 - 11:59 AM

The OP said the ring on the bottom is reflective, so this is definitely a Cheshire.

As Alexis said earlier, Cheshires can be used as collimation caps.


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#13 Vic Menard

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Posted 25 July 2021 - 12:14 PM

The OP said the ring on the bottom is reflective, so this is definitely a Cheshire.

You're right (I fixed my earlier post), I guess I glossed over that since the tool looks like it has been painted.

 

As Alexis said earlier, Cheshires can be used as collimation caps.

Or vice versa...



#14 macdonjh

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Posted 25 July 2021 - 12:23 PM

Thanks, everyone.  I thought the combination tools were often called Cheshire tools because of that 45o cutout.  I didn't know the reflective circle was actually the "Cheshire part".  I could go try my combination tool out, but I'll ask this here anyway: if a primary mirror is a long way from proper collimation, does the reflected ring from the Cheshire form only an arc, instead of a full circle?

 

Anyway, the lack of cross hairs and the 45o cutout is what made me think the OP's device is a collimation cap.  I've got my new fact for the day, school's out.

 

Interesting, sixela's opinion about Hotech collimators.  I like mine.  Granted, I'm no Vic Menard (who of us is?), but it's good enough to quickly get me collimated well enough to enjoy the view.  My two cents.



#15 Starman1

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Posted 25 July 2021 - 12:50 PM

Thanks, everyone.  I thought the combination tools were often called Cheshire tools because of that 45o cutout.  I didn't know the reflective circle was actually the "Cheshire part".  I could go try my combination tool out, but I'll ask this here anyway: if a primary mirror is a long way from proper collimation, does the reflected ring from the Cheshire form only an arc, instead of a full circle?

 

Anyway, the lack of cross hairs and the 45o cutout is what made me think the OP's device is a collimation cap.  I've got my new fact for the day, school's out.

 

Interesting, sixela's opinion about Hotech collimators.  I like mine.  Granted, I'm no Vic Menard (who of us is?), but it's good enough to quickly get me collimated well enough to enjoy the view.  My two cents.

If you can see only part of the reflected ring in the Cheshire, it indicates your secondary collimation is way out.

You first need to address that collimation before using the Cheshire.

A sight tube (long tube with pupil and crosshairs), or a laser should align the secondary to the focuser axis first.

Then the center marker image may not appear in the Cheshire center, but at least it'll be in the field of view, and you'll see the entire bright annulus of the Cheshire reflection.


Edited by Starman1, 25 July 2021 - 12:51 PM.


#16 Vic Menard

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Posted 25 July 2021 - 12:50 PM

...I thought the combination tools were often called Cheshire tools because of that 45o cutout.  I didn't know the reflective circle was actually the "Cheshire part".

Combination tools are called Cheshire/sight tube combination tools because they combine a Cheshire and a sight tube in a single tool--like the ubiquitous economy "Cheshires" that have a cutout window and only the bottom inch or so can actually be inserted in the focuser (hardly economical if you can't use it). Other "workable" combination tools are the Celestron Newtonian collimating tool, the AstroSystems LightPipe, the Catseye TeleCat, and the FLO Premium Cheshire collimating eyepiece.

 

...if a primary mirror is a long way from proper collimation, does the reflected ring from the Cheshire form only an arc, instead of a full circle?

Primary mirror tilt will probably push the reflection off the face of the primary mirror before the Cheshire ring starts to be clipped by the bottom of the focuser. If it's a (longer) combo tool, it may be clipped sooner, and if it's a 1.25-inch combo tool in a larger aperture scope, even more likely. If the secondary mirror is a long way out, it's much more likely. Another thing to watch out for with a combo tool with a cutout window to illuminate the 45-degree polished Cheshire surface is misalignment of the window or improper illumination of the polished surface (both can make the outer edge of the Cheshire ring appear non concentric with the perforation). The simple solution is to use the perforation as the reference, although the tool will likely not work correctly with a common notebook reinforcement ring.


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#17 Starman1

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Posted 25 July 2021 - 12:57 PM

 

Interesting, sixela's opinion about Hotech collimators.  I like mine.  Granted, I'm no Vic Menard (who of us is?), but it's good enough to quickly get me collimated well enough to enjoy the view.  My two cents.

Easy test.

Remove laser, turn 90°, and reinsert.

Still collimated?

Then the laser is accurate and the collimation is repeatable.

Now no longer collimated?

Then the laser is either out of collimation or there is no repeatability of the insertion.

I learned my Glatter laser was out of collimation this way (it is quite old), and I collimated it so it is accurate and repeatable.

If the laser is accurately collimated, but you can't get a consistent registration upon insertion, or if you can get a consistent registration on insertion, but the laser isn't collimated,

then using the tool is miscollimating the scope.


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#18 Orion68

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Posted 25 July 2021 - 02:03 PM

I took another picture of the tool to show that the bottom does indeed have a reflective ring and there is no mirror inside the tube. Tried getting a better picture of the interior of the tube but I couldn't get it centered, hence the dark shadow in the lower, right corner.

 

The tool is a gray plastic and does not appear to have been painted. The outside edges of the barrel of the tool are evenly scored and it appears to be intentional. 

 

The barrel size is 1.25" and fits very tightly in the 2" to 1.25" adapter.

 

Sounds like the consensus is that this is a Cheshire. Thank you all for weighing in.

 

Cheshire Or Other Tool

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#19 Vic Menard

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Posted 25 July 2021 - 02:26 PM

I took another picture of the tool to show that the bottom does indeed have a reflective ring and there is no mirror inside the tube. Tried getting a better picture of the interior of the tube but I couldn't get it centered, hence the dark shadow in the lower, right corner.

 

The tool is a gray plastic and does not appear to have been painted. The outside edges of the barrel of the tool are evenly scored and it appears to be intentional. 

 

The barrel size is 1.25" and fits very tightly in the 2" to 1.25" adapter.

 

Sounds like the consensus is that this is a Cheshire.

Yep, a Catseye 1.25-inch Cheshire.


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#20 CHASLX200

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Posted 25 July 2021 - 02:38 PM

I never get a laser to agree with my Tectron tools.  Have another Orion laser that is off like my other Kendrick laser was off as well. I know the Tectron tools are right.  I gotta wonder if any laser is really right?



#21 Orion68

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Posted 25 July 2021 - 02:40 PM

From the discussion It sounds like a Cheshire (like mine) may not be the best tool for collimating a secondary although it can be used. Since this is the only tool I have this is what I used and it seemed to work pretty well. (with help from Vic, Don, Asbytec & others!)

 

Wondering out loud here:

   - If a star test (real star) shows a good airy disk pattern, the primary must be well collimated, yes?

   - Does the good star test automatically mean the the secondary is also well collimated, yes/no/maybe?

   - Is this question going to take me down an optical rabbit hole, yes?

 

As always, many thanks to all for sharing the knowledge.


Edited by Orion68, 25 July 2021 - 02:46 PM.

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#22 Starman1

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Posted 25 July 2021 - 02:43 PM

From the discussion It sounds like a Cheshire (like mine) may not be the best tool for collimating a secondary although it can be used. Since this is the only tool I have this is what I used and it seemed to work pretty well. (with help from Vic, Don, Asbytec & others!)

 

Wondering out loud here:

   - If a star test (real star) shows a good airy disk pattern, the primary must be well collimated, yes?

   - Does the good star test automatically mean the the secondary is also well collimated, yes/no/maybe?

If you are talking at high power, then yes.


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#23 Orion68

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Posted 25 July 2021 - 02:50 PM

If you are talking at high power, then yes.

Do you mean if the star test was performed at high power and at focus?

Thanks Don.



#24 Vic Menard

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Posted 25 July 2021 - 03:54 PM

I never get a laser to agree with my Tectron tools.  Have another Orion laser that is off like my other Kendrick laser was off as well. I know the Tectron tools are right.  I gotta wonder if any laser is really right?

A lot depends on what alignments you're comparing, the quality/precision of the laser/tools, and the registration of the laser/tools. For a comparison of the various tools and their signature alignments, see here:  https://www.cloudyni...dobs/?p=4651500

 

And for the record, my laser is "really" right.  ubetcha.gif


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#25 Vic Menard

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Posted 25 July 2021 - 04:11 PM

From the discussion It sounds like a Cheshire (like mine) may not be the best tool for collimating a secondary although it can be used. Since this is the only tool I have this is what I used and it seemed to work pretty well. (with help from Vic, Don, Asbytec & others!)

 

Wondering out loud here:

   - If a star test (real star) shows a good airy disk pattern, the primary must be well collimated, yes?

   - Does the good star test automatically mean the the secondary is also well collimated, yes/no/maybe?

   - Is this question going to take me down an optical rabbit hole, yes?

Before short focal ratio sight tubes were available (actually, before most collimating tools of any kind were available), I used my old Tectron Cheshire for assessing the secondary mirror placement (rotation and offset) and I used my Tectron sight tube for secondary mirror tilt. (I also used my Tectron Cheshire for primary mirror alignment--and the square center marker on my primary mirror was calibrated to the Cheshire perforation for optimal precision.)

 

A good star alignment (like Mike Lockwood's http://www.loptics.c.../starshape.html ) is an indicator of optimal primary mirror tilt alignment, it does not indicate optimal secondary mirror alignment (placement or tilt). 

 

Primary mirror tilt adjustment aligns the coma free field to the eyepiece axis.

Secondary mirror tilt adjustment makes the focal plane perpendicular to the eyepiece axis.

Secondary mirror placement centers and balances the field illumination on the eyepiece axis at the focal plane. 

 

Do you see a rabbit hole?


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