Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Development of an Ultimate Combination Tool F/4 to F/6

  • Please log in to reply
41 replies to this topic

#26 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 50,725
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 13 June 2021 - 12:27 PM

Some criticisms of the tool:

1) the crosshairs are too thick for the small center markers on many 8" to 12" commercial scopes and would be difficult to place

over the center of the primary center without obscuring the marker

1a) if the crosshairs are not perfectly in the center, there is no way to make a correction.

2) the illumination of the tool is one-sided so the ring is not visible in twilight without some illumination like a flashlight.

3) It does not insert fully, making it difficult to get the pupil to the focal plane (as has already been mentioned).

4) Just about the only scopes still coming with 1.25" focusers are small (75-120mm) so most of the market would have to use an adapter with your tool

I could foresee making the tool 2", though, with 3D printing.

 

A tool like the Astrosystems Light Pipe answers 1-3 above and also #4 since it is available in a 2" size.

 

One question: since the tool telescopes, how do you prevent an angular error to appear between upper and lower sections?

With the only other telescoping one I know of, the Catseye, the only way I could guarantee alignment of upper and lower sections was to use the tool fully compressed

or use a ruler to get the length the same on all sides.



#27 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted 14 June 2021 - 05:59 AM

Don;

1) The crosshairs are 0.8mm wide and similar to those found in other tools.   

1a) The crosshairs are 3D printed and centred to within 0.2mm.

2) The ring is glow in the dark and can be charged with a flashlight prior to use if wished.  

3)  Agreed and at some point I may try to address this with a longer aluminium barrel.  

4) Yes, I noted that this would need to be used with a Parallizer or similar in 2" focusers.

 

I can make a 2" Tool but this has drawbacks as well.  I prefer the tool be used with something like a Parallizer.  The critical primary collimation is most noticeable when using shorter focal length eyepiece which are most often 1.25".  In my opinion if you are using an adapter, you should be collimating with an adapter.  Hence the reason for a "Universal" 1.25" tool.

 

The angular error is prevented by having the OD of the sliding portion of the tool friction fit with a 1.5" long ID of the fixed portion of the tool. This friction fit over the 1.5" length prevents the moving part from being off axis with the fixed portion.   

 

 

Rob



#28 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 50,725
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 14 June 2021 - 08:49 AM

Rob,

1) 0.8mm is similar to other combination tools, but if you see the result of using 0.5-0.6mm crosshairs instead, you'll realize that they make a big difference when collimating the commercial scopes with the smaller rings on the primaries.

It is far easier to center the crosshairs in the center of the primary rings.

2) The friction fit has to have some clearance to be able to slide.  It is still possible for the sections to be off angle relative to one another.  I suggest a threaded attachment instead of a slip fit.


  • steveincolo likes this

#29 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted 14 June 2021 - 09:25 AM

Don;

 

1) Great comment, Thanks!!  I will try reducing below 0.8mm. The printer nominal nozzle diameter is 0.4mm for standard 3D printing. 0.8mm is 2 print widths.  I can go to a smaller nozzle (0.3 or 0.2) but then the print times get really really long.  Print times change with the square of the nozzle radius so dropping in size really increase the print time (which is already 6 hours).  I will try printing 0.4mm (single print line width) and see what I get but I think it will be too easy to fracture.  Regardless, I will play around a bit and see if I can get finer.    

2) The outer diameter of the sliding tube is actually bigger than the inner diameter of the outer fixed part.  There is about 0.1mm interference between the parts and the inner sliding tube is actually compressed inward slightly due to the interference.  This is part of the beauty of using plastic, it is flexible and less stiff than metal. This interference ensures the moving tube remains coaxial with the barrel and does not go off axis.  I spent a lot of time on this to get it right!  I assure you that it holds its axis very well, I made a lot of test samples (20+) of this configuration to get it right.  

 

Rob 



#30 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 18,418
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 14 June 2021 - 04:09 PM

I suggest a threaded attachment instead of a slip fit.

 

A threaded cross hair nose piece attachment, one for f/4 and the other for f/6, offers freedom to allow the pupil end to slide in order to address the focal plane concerns above. You don't even have to get rid of the cutout, it will stow inside the tool when the pupil end is fully inserted as a site tube and still be useable when extended as a collimation cap or Cheshire. I am not sure a small amount of slip (or twist up) clearance at the top end will matter a whole lot when aligning the primary axis. Just a thought...



#31 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted 14 June 2021 - 05:23 PM

A threaded cross hair nose piece attachment, one for f/4 and the other for f/6, offers freedom to allow the pupil end to slide in order to address the focal plane concerns above. You don't even have to get rid of the cutout, it will stow inside the tool when the pupil end is fully inserted as a site tube and still be useable when extended as a collimation cap or Cheshire. I am not sure a small amount of slip (or twist up) clearance at the top end will matter a whole lot when aligning the primary axis. Just a thought..

Norme.  Good idea, basically have the barrel slide up and down and crosshair slide inside as well.  I will consider if I can do it, the ID may get too narrow.  Also, I am trying to avoid making multiple versions of the tool so I would rather have a single tool.    

  

FYI - Threads would have much more play than my current tool.  It really works well the way it is.   

 

Rob  



#32 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 18,418
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 14 June 2021 - 08:26 PM

Rob, yes a single tool is a good goal. I agree, we don't want the ID to be too narrow, especially at the cross hair end. I don't know if threads will add to the thickness of the ID, you'd know better than me. I'm not clear on why they'd have more play then a slip model. Just following your thread when Don's idea caused me to think about and share it.

#33 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 01:00 PM

All;

  Taking your advice, I have reduced the length of the top by 50% it is now 1", 25.4mm high above the adapter or drawtube.  This will ensure the pupil can be at or closer to the focal plane.  In testing, I found it worked well for the primary, regardless of the distance from the focal plane.  The gap between the mirror marker and Cheshire ring just changed ever so slightly but did not reduce my ability to accurately align the primary.  The entire primary of in my F/4.7 was easily visible.  I will now need to make a longer sliding portion for F/6 so there will now be two tools F/4 to F/5 and F/5 to F/6.   

 

In shorting the height, I found that I was often shining the flashlight into my eyes rather than the tube. To this end, I have added a light shield.  Not only does this protect the eyes but it guides more light into the tube.  

 

To Don's point, I have reduced the width of the crosshairs to a miniscule 0.4mm wide.  This is much thinner than any of the other tools I have purchased or made.  Surprisingly, they show good strength.  I also again tested smaller pupils.  I tested a 1mm pupil and again found it too small.  1.5mm seems to be the smallest pupil that works well.

 

I don't think I can go shorter without using a longer aluminium sleeve, which I don't have access to at this point. 

 

For some further perspective... This tool, for the vast majority of mass produced telescopes, will do everything that a Telecat will, and can also be used as a Cheshire without the sliding portion.  This tool would cost $60 or less depending on the volume.  This is less than 50% of the Telecat. 

 

 

Ulimate Shorty 1.jpg

Ulimate Shorty 2.jpg

Ulimate Shorty 3.jpg

 


  • sixela likes this

#34 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 01:12 PM

Rob, yes a single tool is a good goal. I agree, we don't want the ID to be too narrow, especially at the cross hair end. I don't know if threads will add to the thickness of the ID, you'd know better than me. I'm not clear on why they'd have more play then a slip model. Just following your thread when Don's idea caused me to think about and share it.

I think this is a really good idea but it will end up being expensive.   

 

Making tight clearance threads is difficult in larger diameters and cutting the tight clearance threads can only be done on a lathe.  Using a tap it is really really difficult to get the threads parallel to the desired axis.   So....at this point I don't have a lathe so I am stuck using the 3D printer.  My 3D printer simply won't make threads that will have the required tolerances, thus my choice to use the interference fit of the sliding tube.   

 

I am really trying to keep this tool low cost.  As soon as it goes on a lathe, I am paying a machinist to make the tool and or someone has to watch the CNC lathe and run it.  On the 3D printer, I hit go, come back 4 to 6 hours later and the tool is essentially done, all you have to do is put  the top on and slide in the tube which takes 60 seconds.  This keeps the production cost really low.  I am trying to make a tool for the masses.  If I go the machined aluminium direction, it will end up costing the same amount as a Telecat.  My goal is a tool that does everything that a Telecat does, and more, for less than half the price.  I want this tool to be used by those buying the XT8, AWB, Starblast, etc. who don't have access to relatively low cost tools for collimation.

 

 

Rob  


  • Asbytec likes this

#35 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 50,725
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted Yesterday, 02:35 PM

Your Competition is really:

Astrosystems LightPipe--$49-$56

Celestron Collimation eyepiece: $38-$47

I don't think you can compare yours to the all-aluminum, machined, Catseye TeleCat.

 

One other thing: the 1.25" section at the bottom of the telescoping tube, when the tube is telescoped out to, say, an f/6 length, may be outside the bottom of the focuser's drawtube,

which eliminates the extra degree of tube registration the 1.25" section is designed to provide.  Hence, I see no reason to have the printer print that extra width of tube at that point.

I suggest you make the material a dark material so it doesn't look like a $0.49 plumbing part and to make it easier to justify the price.



#36 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 05:06 PM

Don;

  The Telecat is a perfect comparison.   Same accuracy, half the cost.   All dimensions of the tool are maintained to within 0.1mm (±0.002") or better.  Also, if you drop my tool, it bounces.  Drop the Telecat and it dents.  My tool is more rugged and robust.  Telecat may have slightly better control on diameter (±0.001"), which is why I am using an aluminium barrel, but the crosshairs on my will be equally or better centred because they are integral to the print.  The placement of the Cheshire ring is also extremely precise, again within 0.1mm.  It is a very comparable tool.  3D printing is now used preferentially for many components from car parts to jet engines.  This tool is comparable and half the cost.  It is made of ABS which will not deform even if boiled in water.   It is dimensionally stable to over 200°F.  I would describe my tool as CNC fabricated (a 3D printer runs on G code just like a CNC mill or lathe).  The tool has been engineered to take advantages of the 3D printers advantages and avoid all its advantages (my 3D printer maintains tolerances really well but doesn't print fine features smaller than 0.4mm, i.e. it does not print threads well.)        

 

I realize the Lightpipe and Celestron tool will be competition but I still feel this tool has advantages.  It does more, its Cheshire feature is particularly nice.  I own the Celestron tool and the Celestron really does not compare well, it is too long to centre the secondary at F/5 (I cut mine shorter) and is not particularly good for the primary alignment (hard to see).      

 

FYI - The sliding tube never exits the 1.25" barrel portion so registration is never lost, it is always equally registered regardless of its length (this was by design).   It is equally registered at its shortest length and longest length.   

 

The material is intentionally light grey because it provides better illumination for aligning the primary.  On telescopes that do not have a reflective mirror marker, the grey background is required to provide a light surface to make the mirror marker visible such that it can be centred in the Cheshire ring.  With a black or dark background, the non-reflective mirror marker is not visible unless you use 2 flashlights, one to illuminate the Cheshire and one down the tube to illuminate the mirror maker.  The light grey colour is an important feature.   Again, this is also a Cheshire and not just a typical combo tool.  Furthermore, it is a Cheshire that works without the need to replace the mirror marker with a reflective mirror marker.    The choice of colours is a design feature.  

 

This tool has been very carefully engineered with many many iterations to get it where it currently is.   

 

Rob



#37 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 50,725
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted Yesterday, 05:16 PM

Rob,

One question I forgot to ask: is the center dark area in the Cheshire calibrated to the small markers on many commercial scopes, or the larger after market center markers like the Farpoint/Catseye triangles and Catseye Hotspot?

I can't tell from your images which size center marker the tool is optimized for.

If the larger ones, I have found in the field that getting a perfectly-centered Center marker in the Cheshire is difficult when the marker is significantly smaller than the center dark area in the Cheshire reflection.

Of course, that is preferable to the reverse, where the small marker fits the dark area well and the larger markers overlap the edge of the tool's center dark area.

 

Your statement, "FYI - The sliding tube never exits the 1.25" barrel portion so registration is never lost, it is always equally registered regardless of its length (this was by design).   It is equally registered at its shortest length and longest length" is conditional--based on the length of the focuser's drawtube and the f/ratio of the scope.  And, of course, is is not applicable when the tool is used in a 2" focuser with an adapter.


Edited by Starman1, Yesterday, 05:18 PM.


#38 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 05:24 PM

Don;

   I have different Cheshire rings I can pop in.  Currently there are 2, one that is 19mm diameter matching the Farpoint triangle and one that is 14mm diameter (ID) which works for standard ring mirror markers.  It would take me 5 min. to make a ring that fits any diameter a customer requests.  Because the ring is printed separate, it can be printed for the customers requirements.

 

With respect to registration, you are right.  The sliding tube is equally registered in the tool at any length.  The tool registration in the larger system is dependent on registration in the drawtube and adapter.  I envision using this tool with a Parallizer or similar in 2" drawtubes.  I personally feel that 1.25" tools with precision adapters are better than 2" tools.  We should collimate with the adapter we are going to use for high magnification viewing (i.e. 1.25" eyepieces), the adapter should be part of the collimation of the system (unless you are only using 2" tools and not an adapter or are doing AP). 

 

Rob



#39 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 05:24 PM

FYI -  All of this is good input... thanks all!  Your suggestions will make this tool better.



#40 Vic Menard

Vic Menard

    Cosmos

  • *****
  • Posts: 8,184
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted Yesterday, 05:38 PM

...With respect to registration, you are right.  The sliding tube is equally registered in the tool at any length.

I can understand lateral registration not changing, but if the sliding tube is barely inserted in the aluminum receiving tube, I suspect there would be a good chance for potential tilt error (the other registration issue). (Have you resolved the parallax error(s) you were dealing with in your alignment images?)

 

...I personally feel that 1.25" tools with precision adapters are better than 2" tools.  We should collimate with the adapter we are going to use for high magnification viewing (i.e. 1.25" eyepieces), the adapter should be part of the collimation of the system (unless you are only using 2" tools and not an adapter or are doing AP). 

I think 1.25-inch tools are better for 1.25-inch focusers. From f/4 to f/5 (half of your tool range--i'm still not clear how that's related to a scope's actual focal ratio), it's quite possible that the user will also employ a coma corrector. If the coma corrector is a 2-inch accessory, I would suggest the collimation match the corrector, not the high magnification eyepieces (which may, or may not, be 1.25-inch) that will be inserted in a 2- to 1.25-inch adapter that comes after the coma corrector. 


  • Jon Isaacs likes this

#41 MellonLake

MellonLake

    Apollo

  • *****
  • topic starter
  • Posts: 1,459
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted Yesterday, 08:22 PM

The sliding tube is always in full contact with the length of the aluminium receiving tube at the focal lengths I have quoted. You can extend it farther but it is not recommended.  

 

Yes if you have a Coma corrector you should use the 1.25" tool in a good adapter like a Parallizer or use a 2" tool.  However, the Parallizer converts 1.25" tools to 2" tools effectively.  In fact based on my testing, the OD cut out in the Parallizer actually makes the Parallizer with a 1.25" tool better than a 2" tool as the Parallizer registers more consistently in the drawtube.  This is why I suggest the Parallizer and the 1.25" tool because it is actually in my opinion superior at registering than 2" tools.  With a coma corrector I would use the Parallizer and 1.25" tool to collimate without the Coma corrector and then use the Parallizer in the Coma corrector for viewing with 1.25" tools.   

 

Rob  



#42 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 18,418
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted Yesterday, 10:50 PM

I like the idea of it not bending when dropped. I've dropped one of mine, unfortunately not on the grass outside. I had to hammer it back into round so it will fit in the adapter and measure and adjust the cross hair to ensure centricity. 




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics