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

Who wants to make a Ross Null Lens?

  • Please log in to reply
174 replies to this topic

#1 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 08 August 2020 - 01:25 PM

I did.  And here's how:

If anyone is interested in obtaining a decent Ross Null Lens of known quality, I suggest making one yourself.  I made this one shortly after Ceravolo published his article on the use of one over 20 years ago in TM magazine.  I ordered BK7 blank (4”) and tool glass (Pyrex) from United Lens. A machinist friend made a wedge testing jig and a two ball spherometer (not pictured) which assisted in reaching ROC of the convex side.  I also used wet tool and sun, knife edge and ronchi testing on the tool to measure radius.  Once I hit close to target, and finished fine grinding I began polishing lens and the tool so that I could fringe test the lens convex side against the tool once I established that tool was spherical.  To polish the tool, I made convex dental stone tool cast against the tool. The small triangular bits of tape spaced 120 degrees apart on the outer edge of the tool from testing are still apparent. The plano side took longer.  Bob Folllet’s widow had given me one of his 5” optical flats which I used to fringe test the plano side.  It’s depicted as well.  Bob had told me that when he and his dad made flats, they were figured until there was no deviation from straight lines on the flat.  The other devices pictured are a spacing rod from object to lens used in a  project and a jig to measure and determine wedge.  I was not able to detect wedge in the lens after correcting as best as could being limited by my ability to measure it beyond .0001”.  The jig and the spherometer shared a dial indicator.  The spacing rod is a section of carbon fiber rod (arcane description of the salvaged broken tip of fishing rod) with ball bearings epoxied in when I was satisfied of the measurement by repetitive sanding one tip end and measuring with ball bearing in place.  The opposite end had a fixed ball bearing in place.  I used the lens for a handful of projects supplementing Foucault and star testing.  The skills necessary to make a RNL are rudimentary to anyone who has figured a mirror, provided one has means to test the plano side either by optical flat or patient enough to master the Raleigh water test. (I suppose a biconvex lens could be made without the optical flat as the software anticipates biconvex.)  I worked both sides until I was able to obtain straight fringe lines (I don’t remember the count but I believe 3 or 4) but they were arrow straight to within .5” of the edge.  I can’t find the log which in I had sketches illustrating the progress, but it’s long gone.  I masked off the outer .5” to give a clear 3” aperture of lens.  Gil

imageedit_20_5600422504.jpg


Edited by GLS, 08 August 2020 - 01:39 PM.

  • PrestonE, LarsMalmgren, Pinbout and 5 others like this

#2 Matthew Paul

Matthew Paul

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 06 Jun 2016
  • Loc: Orange County, New York

Posted 08 August 2020 - 02:14 PM

I love seeing things like this. Thank you for sharing. 


  • PrestonE likes this

#3 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,779
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 08 August 2020 - 03:09 PM

 You can save yourself some time and use an   already made plano convex lens and refiguring it.  What is important is the  transmitted wavefront, so the flat surface doesn't need to be  dead flat just optically smooth. If you get  it flat to 1/2 wave that will be fine. You need to grind  polish and figure a concave test plate to test the convex surface. It doesn't need to be fully polished out, just enough polish to test and figure it a sphere and you'll then be able to see fringes to test the convex surface with it.

   As stated one can also use a double convex lens, so you might look into "borrowing"  the convex element from an achromat. You can test the assembled achromat by double pass autocollimation to determine the quality of the achromat. If it tests well the odds are very good that the convex element by itself will also be very good. 

 

                   - Dave 



#4 Gleb1964

Gleb1964

    Vostok 1

  • -----
  • Posts: 136
  • Joined: 13 Jul 2016
  • Loc: Sweden

Posted 08 August 2020 - 05:37 PM

    As stated one can also use a double convex lens, so you might look into "borrowing"  the convex element from an achromat. You can test the assembled achromat by double pass autocollimation to determine the quality of the achromat. If it tests well the odds are very good that the convex element by itself will also be very good. 

 

                   - Dave 

That is not enough. You need all prescription of lens - radiuses, thickness and refraction index for test wavelength (or glass type) to be able to calculate test configuration.

 

Gleb 


  • Mark Harry likes this

#5 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 08 August 2020 - 06:04 PM

That is not enough. You need all prescription of lens - radiuses, thickness and refraction index for test wavelength (or glass type) to be able to calculate test configuration.

 

Gleb 

Dave is just giving a simpler way to test the lens, which should already have those known attributes.


Edited by Pinbout, 08 August 2020 - 06:05 PM.

  • DAVIDG likes this

#6 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 08 August 2020 - 06:34 PM

David, the tool that was used to make the convex surface was not polished out.  As you recommend, it was polished just enough to ensure it was spherical.  Your point is well taken about correcting an available plano convex lens, but after looking, I didn't find suitable candidates.  Having previously made the 4.25" Fraunhofer aplanat, I had the necessary equipment on hand and knew it wouldn't be a job too big for my skills to spend the time grinding and polishing both sides.  (It's another good point you made about using the biconvex lens in my refractor.  I could have used the tools (that I still have) to fringe test the lens .)  But that would have involved some disassembly required and putting it out of commission for the time being.  All these are my after thoughts.  It never dawned on me at the time to use it.    By making it from scratch from Grade A Schott BK7 with an invoiced refractive index stated to five decimal points, I eliminated an unknown variable of a lens with uncertain heritage (as to your first recommendation.) In this hobby I am looking for a way to murder time, not save it. wink.gif  The horse left the barn close to a quarter of a century ago with this project galloping away with the could've, should've and would've. wink.gif Gil


Edited by GLS, 08 August 2020 - 07:18 PM.


#7 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,779
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 09 August 2020 - 02:11 PM

That is not enough. You need all prescription of lens - radiuses, thickness and refraction index for test wavelength (or glass type) to be able to calculate test configuration.

 

Gleb 

 True, but if you  buy a lens you need to know these as well.  If buy one and it is not a certified as to it's exact quality  which cost big money ( Ceravolo I believe is selling one for a few hundred dollars) your  going to have check the values so you need the proper tools. Same goes if you make a lens from scratch or refigure one.

    The facts are that a majority of stand achromats of  the fraunhofer  design use BK-7 as for the crown element. The bottom line is that if your going to do the Ross Null test correctly you need know to all the characteristic of the lens. So if you don't have them you need to measure them and if your going to make one from scratch you'll need the right tools to measure  them as well.

    As stated by Danny ( Pinbout ) what I'm trying to point out that  you might have already suitable lens by using the crown element in achromat and you can test the complete achromat by a star test or double pass and get a good idea of it optical quality. 

 

 

               - Dave  



#8 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 09 August 2020 - 07:53 PM

If buy one and it is not a certified as to it's exact quality  which cost big money ( Ceravolo I believe is selling one for a few hundred dollars) your  going to have check the values so you need the proper tools.

Ceravolo's lens cost $650+S&H two years ago and is certified at 0.1 wave surface. I doubt too many ATMs will be able to reproduce that. Remember, the Ross lens has to be twice as good as the mirror under test.


Edited by MKV, 09 August 2020 - 07:55 PM.

  • Mark Harry likes this

#9 Mark Harry

Mark Harry

    Cosmos

  • *****
  • Posts: 8,798
  • Joined: 05 Sep 2005
  • Loc: Northeast USA

Posted 10 August 2020 - 07:32 AM

What Mr. Groski doesn't say, is where you are going to get the precise tools to make the check.
To me, access to an IF comes to mind, and I don't mean one built in a garage, either.



#10 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 10 August 2020 - 10:36 AM

Not made in my garage, but on a kitchen counter in the last century.  The photo with the fewest lines is of the convex side with outer .5" masked.  The one with the more numerous lines is the plano side, unmasked.  I couldn’t find thinner spacers for the plano hence the more numerous lines even with finger pressure, but the convex’s tool had the spacers on it from over 20 years ago.  My recollection of testing when I made it was that the plano side’s fringes were arrow straight with only a few lines appearing.  Same with the convex side. The Newton interferometer was made by a late TNer in the 1960s.  I re-powered it with neon tubing from a donated beer sign.  I don’t know how to make the lines any straighter on the convex side.   I mask off the outer .5”  reducing the clear aperture to 3”.  I probably could go to more open aperture, but there’s no need to do so as any foreseeable project doesn’t utilize the full 3”.  The glass beam splitter is as dusty as South Texas in a drought.  I haven’t used it since the last century.  If I get around to it, I’ll clean the dust off and maybe take better photos when it's a little darker inside my not exactly NASA clean room/optical lab

imageedit_20_6100589387.jpg imageedit_9_8742073529.jpg

Attached Thumbnails

  • imageedit_22_8776257445.jpg

  • Pinbout likes this

#11 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 10 August 2020 - 10:53 AM

imageedit_23_4926846832.jpg Light source.  I actually traded the donated sign to a man who made the neon tubing for my  IF.  The tubing is reflected in the photo above of the convex side and it's not a defect in the fringes.  Gil


  • LarsMalmgren likes this

#12 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,779
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 10 August 2020 - 11:34 AM

What Mr. Groski doesn't say, is where you are going to get the precise tools to make the check.
To me, access to an IF comes to mind, and I don't mean one built in a garage, either.

 You need a spherometer which many you can make and also double check the radius on the concave test plate via Foucault measurements.  You need a lens thickness gauge which is easy to make.  GLS showed picture of his and I made one very similar for around $25. A monochrome or semi monochrome light source so  simple CFL bulb will work for $2. A optical flat to test the rear surface. I have a box full of them that I have purchased off of Ebay that are flat to at least 1/10 wave , and most were under $50. If you get the straight interference fringes on both surfaces you'll have an excellent lens for considerable less money then a Ceravolo unit. GLS as shown it can be done and I  most advanced ATM's will no no problem making a high quality lens.  Also it needs to pointed out that in most cases  the full aperture of the lens is not used. So the smaller the aperture, the greater the odds that over that area the wavefront is excellent. 

    Sure if your going to make 25" f/3.5 mirror you need a very high quality lens but you undertaking an advanced project like that you need to understand what the quality of the test(s) you need to achieve the results you want. If not then then your asking for poor results. There is no free lunch. 

    The bottom line is the  Ross works and just like any test you need to double check the results. If you want to look at a test that has major issues with fast optics just do a statistical  Gage RR test on doing the Foucault measurements which you show you all the sources of errors  both from the instrumentation used and  also errors from  the user. It will then tell  what the statistical confidence level is  with those errors and what  the errors need to be reduced to so when you say your mirror is good "1/10" wave there is Plus/Minus value that shows that it truly falls in that range. 

 

 

                  - Dave 



#13 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 10 August 2020 - 01:59 PM

attachicon.gifimageedit_10_4365791346.jpgNot made in my garage, but on a kitchen counter in the last century.  The photo with the fewest lines is of the convex side with outer .5" masked.  The one with the more numerous lines is the plano side, unmasked.  I couldn’t find thinner spacers for the plano hence the more numerous lines even with finger pressure, but the convex’s tool had the spacers on it from over 20 years ago.  My recollection of testing when I made it was that the plano side’s fringes were arrow straight with only a few lines appearing.  Same with the convex side. The Newton interferometer was made by a late TNer in the 1960s.  I re-powered it with neon tubing from a donated beer sign.  I don’t know how to make the lines any straighter on the convex side.   I mask off the outer .5”  reducing the clear aperture to 3”.  I probably could go to more open aperture, but there’s no need to do so as any foreseeable project doesn’t utilize the full 3”.  The glass beam splitter is as dusty as South Texas in a drought.  I haven’t used it since the last century.  If I get around to it, I’ll clean the dust off and maybe take better photos when it's a little darker inside my not exactly NASA clean room/optical lab

attachicon.gifimageedit_10_4365791346.jpg

attachicon.gifimageedit_20_6100589387.jpgattachicon.gifimageedit_9_8742073529.jpg

You should use a collimating lens to do your Newotnian fringes. Fresnel lenses work well. There's no point in showing an igram with so many fringes. If you're trying to make a credible claim, that's not the way to do it, and I think you're perfectly aware of that. Incidentally, I have a similar viewer which can accommodate a Fesnel collimator, with a slightly tighter coil, which I had made in a neon-sign shop. The glow is orange-red. and needs filtering. If you don;t have a collimating lens then you must take igrams form a very long distance to avoid parallax issues.,



#14 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 10 August 2020 - 02:03 PM

The bottom line is the  Ross works and just like any test you need to double check the results. If you want to look at a test that has major issues with fast optics just do a statistical  Gage RR test on doing the Foucault measurements which you show you all the sources of errors  both from the instrumentation used and  also errors from  the user. It will then tell  what the statistical confidence level is  with those errors and what  the errors need to be reduced to so when you say your mirror is good "1/10" wave there is Plus/Minus value that shows that it truly falls in that range. 

Bottom line, Dave, is that amateur optics with high ratings need to be professionally checked using industry's standards, not one's own amateur tests.


  • Mark Harry likes this

#15 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 10 August 2020 - 04:40 PM

MKV, your points are well taken.  In ATMing , as in life, better is always the enemy of good enough. 

I wouldn't discourage anyone from attempting to make a Ross Null Lens simply because a professional could make a better one.  I've found the one I've made to be useful for my purposes, but I also use a battery of other tests available.  Rather than wring one's hands about someone else making a better one, put grit to glass and make one, and test it with the resources available or as has been suggested, test and improve if necessary a surplus one.  A spherometer is helpful, but a template made from window pane glass is also useful in making one from scratch.  Clamp a glass cutter to a wooden batten, screw the batten to piece of wood at the target roc on which the glass sits, scribe the glass with the makeshift compass.  Break along the cut and use the template during rough grinding.  It's more durable than cardboard and works fine on small apertures where the ROC doesn't have to be made to exactitude.

 

Gil


Edited by GLS, 10 August 2020 - 04:40 PM.


#16 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 10 August 2020 - 05:42 PM

GLS, I couldn't agree more. This isn't about discouragement at all. To the contrary. I encourage people who claim their optics are equal to or better than the high-end professional  optics to have their home-made ones tested by the same industry standards to lend credence to their claim and have their skill recognized..  



#17 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 10 August 2020 - 08:04 PM

As indicated in my first photo earlier today of the plano side of the fringe pattern, the shim material was too thick which yielded numerous fringes. It was not my intent to deceive anyone of the actual flatness of the lens's plano side.  Tonight I found better material and this is the result.  Hooks on outer lines are masked giving a 3" aperture.  Photo was taken at right angle to lens off the reflection of the 45 degree angled sheet of float glass. 

As Homer said to Wilbur: "That'll do, pig".  

 

Gil

imageedit_25_6443303478.jpg


Edited by GLS, 10 August 2020 - 08:09 PM.

  • Pinbout likes this

#18 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 12 August 2020 - 08:11 AM

One way to make a test plate as DavidG suggested to test a RNL of unknown quality would be to use a hammered steel tool.  Here’s one 4” in diameter that I hammered out to a known target radius of curvature monitored by templates I cut from window pane glass.  Another way to monitor target of an unknown ROC is to make a simple comparator.  Cut from plywood with a hole cutter, a oversized thumb screw with a rounded tip (solder blob)  is screwed into the wood at center established by the hole cutter’s pilot drill bit.  On the outer edge, ball bearings are epoxied 120 degrees apart.  The screw is adjusted so that the balls don’t teeter on the lens surface which establishes curvature.  A glass or tile tool’s curvature can be checked during grinding and a hammered tool’s curve established at outset.  The hammered steel technique was pioneered by wok manufacturers among others and adopted by ATMers during the Mak craze. There is not much new under the ATM sun. My project was to make a 3” reference element (negative lens) in a Fizeau interferometer design by Ceravolo.  The steel tool makes short work out of rough grinding while preserving edge thickness.  I poured a dental stone tool covered with tiles to fine grind.  I abandoned the project with a clear conscience when life got in the way in the last century.  I’m beginning to wish I hammered out a metal tool for an F/2.7 6” mirror that I am currently in the throes of rough grinding with a metal ring tool.  Gil

imageedit_29_8123688046.jpg imageedit_26_9765325414.jpg imageedit_31_5660010699.jpg


Edited by GLS, 12 August 2020 - 09:52 AM.

  • Pinbout likes this

#19 ccaissie

ccaissie

    Surveyor 1

  • *****
  • Posts: 1,964
  • Joined: 13 Sep 2010
  • Loc: Whitefield, Maine

Posted 14 August 2020 - 04:04 PM

I do.  I received one with igram in a pile of stuff I got when cleaning out an optician's cellar.  I sold it for WAY too little....sort of a trial... the first item sold from the pile.  As mentioned it had a sheet with igram and glass type refractive index etc. 

 

I bought a blank from Surplus Shed described as https://www.surpluss...item/L3626.html thinking to make one.  There's enough grinding left to do so making a glass-blocked tool on plaster would probably have time to contact.  I worked out the rough radius to shoot for using the description and CAD and it seemed ballpark for a Ross.

 

Will check for stresses, but it looks good.

 

Brilliant idea using a refractor crown. 

 


  • LarsMalmgren, Pinbout and GLS like this

#20 Mark Harry

Mark Harry

    Cosmos

  • *****
  • Posts: 8,798
  • Joined: 05 Sep 2005
  • Loc: Northeast USA

Posted 15 August 2020 - 06:37 AM

Got a mess of blacksmith tools, and never thought of HAMMERING a tool for grinding.
Brilliant. (me, DUH!)


  • PrestonE likes this

#21 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 15 August 2020 - 10:03 AM

More power to anyone who wants to give this a try but do remember: In the Ross null test the light goes through the lens twice (double pass), doubling its errors.

 

This means that the lens errors (which are doubled) have to be (insignificant) compared to the errors you will tolerate for the test mirror. Example, you wish to make a mirror whose wavefront errors will not exceed 1/20 wave rms. Your Ross lens, with errors doubled, must have a combined wavefront error much smaller than that.

 

That's a lot to ask for. I understand that some dismiss science and go only for "straight bars," but there's a good and logical reason why Ceravolo designed and manufactured his Ross null lens to undustrial precision tolerances (including homogeneity grade glass among other things).

 

Please note that he never and nowhere advocates the use of commercial-grade PCX lenses, which have become the standard "staple" in ATM Ross null testing.

 

Also, it is often mentioned that the highly successful Delmarva mirror making class used the Ross null test equipped with Cervaolo's lens (selling for $600 plus S&H), which may explain why they say their results were comparable (whatever that means) to the results obtained with an autocollimation tester. 

 

And if you wonder what are the tolerances required for Cervolo's precision lens, here's a sobering little chart to help you understand this better

 

Cheers!

 

radii_errors_tolerances.jpg

 

_____

PS  Even if you feel up to the challenge, before embarking on this voyage, you may wish to  consider making the Maksutov null test for paraboloids (often referred to as the 'Waineo' null test), as a more plausible choice.

 

The following are advantages of the Maksutov over the Ross test:

 

(1) the reference element isn't traversed twice

(2) the light source doesn't need to be monochromatic (your LEDs are not monochromatic, so this is a source of error as well),

(3 ) the reference element is a mirror (one surface instead of two for the lens),

(4) the reference mirror can be tested to high precision (better than 1/20 wave surface) with a knife edge at CoC

(5) you don't need to to grind, polish and figure a separate concave reference plate. I don't kn ow about others, but this sure makes more to sense form an ATM's point of view.

(6) the reference element (mirror) can be as small as 1/2 to 3/4 of  the diameter of the test mirror.


Edited by MKV, 15 August 2020 - 10:44 AM.


#22 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 15 August 2020 - 11:15 AM


(5) you don't need to to grind, polish and figure a separate concave reference plate. I don't kn ow about others, but this sure makes more to sense form an ATM's point of view.

 

This wasn't necessary in my experience.  The tool was the contact plate which was flash polished and used to establish exact radius of curvature of the convex surface and fringe test it as well.   I don't believe Tom ever claimed the Waineo test to be his invention.  Others may have named it after him.  Tom was a real pro who in a long career made optics including some under government contracts for satellites.  He would help any amateur who asked for help and was generous in helping me with his time.  He was humble as well.  The Waineo mirror I made needs to be re-cored  and afterwards fine ground, polished and re-figured as necessary as the present aperture size limits its usefulness.  I may or may not get around to it as it has been in its can since 1999 when it was aluminized.  Shiny little devil.   The reason I started this thread was because the RNL test seems to be popular and in use by ATMs here.   At least two skilled ATMs here verify its utility and quality based upon verification via autocollimation which speaks volumes to me and others.   Perhaps someone should start a thread on the Waineo null test and lead with the caveat to make sure the center hole is big enough for present and future projects.  Gil

imageedit_8_7680231551.jpg


Edited by GLS, 15 August 2020 - 01:43 PM.

  • LarsMalmgren likes this

#23 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,779
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 15 August 2020 - 01:05 PM

"This means that the lens errors (which are doubled) have to be (insignificant) compared to the errors you will tolerate for the test mirror. Example, you wish to make a mirror whose wavefront errors will not exceed 1/20 wave rms. Your Ross lens, with errors doubled, must have a combined wavefront error much smaller than that."

   

      Just to clarify that is the transmitted wavefront error not the surface errors.  That reduces the surface errors that is required.  Also a majority of the time you are using a  sub diameter of the full aperture of the lens so it only this section of the lens that needs to meet your standards.

    I'll say it again from all my hands on  first person experience in using this test and teaching the Delmarva class with it, the test wasn't the problem, the problem was getting the mirror to null out. That was  major issue  and will be for any one using it or any Null methods.  It not like you figure for 30 minutes and your at dead straight lines but when you star test you got a 2 wave mirror.  So people are putting the "cart before the horse".  Throwing away the Ross Null because you believe it won't be accurate enough is not the problem. The problem is figuring the mirror to show a null. When it does the mirror will be close if not great. That is when you start using other tests to confirm the results. 

   By the way at the Delmarva class we used other Ross Null lenses besides the one the Swayze brought. 

 

              - Dave 


Edited by DAVIDG, 16 August 2020 - 11:51 AM.

  • Jeff B, LarsMalmgren and Pinbout like this

#24 MKV

MKV

    Cosmos

  • *****
  • Posts: 9,065
  • Joined: 20 Jan 2011
  • Loc: Southeast, USA

Posted 15 August 2020 - 03:19 PM

 

(5) you don't need to to grind, polish and figure a separate concave reference plate. I don't kn ow about others, but this sure makes more to sense form an ATM's point of view.

 

This wasn't necessary in my experience.  The tool was the contact plate which was flash polished and used to establish exact radius of curvature of the convex surface and fringe test it as well.   I don't believe Tom ever claimed the Waineo test to be his invention.  Others may have named it after him.  Tom was a real pro who in a long caeer made optics under government contracts for satellites.  He would help any amateur who asked for help and was generous in helping me with his time.  He was humble as well.  The Waineo mirror I made needs to be re-cored  and afterwards fine ground, polished and re-figured as necessary as the present aperture size limits its usefulness.  I may or may not get around to it as it has been in its can since 1999 when it was aluminized.  Shiny little devil.   The reason I started this thread was because the RNL test seems to be popular and in use by ATMs here.   At least two skilled ATMs here verify its utility and quality based upon verification via autocollimation which speaks volumes to me and others.   Perhaps someone should start a thread on the Waineo null test and lead with the caveat to make sure the center hole is big enough for present and future projects. 

I never suggested Tom Waineo claimed to be the inventor of the test (he was just born when D. D.Maksutov invented the test). Tom is certainly credited for popularizing that test among ATMs, which certainly places him in the Hall of Fame of amateur telescope makers.

 

Of course, your you didn't need to grind a separate concave for a template in your case (some people use tiled or channeled tools for grinding which cannot be used as templates ), but you still have to grind, polish and figure the flat side. Plus, the lens central thickness has to be within tight limits as well. And of course, the template also has to be polished and figured precisely spherical -- so there you have it, three or four surfaces vs one

 

The Maksutov null, which came to be known as the 'Waineo' null test in the 1960's, is not well known at all among ATMs today, and very few people nowadays have used it and can speak from first-hand experience about it. This is why there's little chance of it being revived anytime soon as a better suited test for ATMs then the Ross null test. 



#25 GLS

GLS

    Explorer 1

  • -----
  • topic starter
  • Posts: 56
  • Joined: 01 Aug 2020

Posted 15 August 2020 - 04:40 PM

Making a quality lens with simple tools that some find invaluable in use can be as rewarding an effort as making a Newtonian mirror.  Or maybe it's just me.   I didn't see it as a waste of time.   You couldn't make it any clearer you do.  Why would anyone want to make a crown and flint achromat when the same aperture or larger reflector is easier, taking less time to make and is not beset with color issues absent with reflectors?  That's four surfaces to one not counting the diagonal.  What's the point of making telescopes when we can see better images from Hubble?  

Please take the time in another thread to show us how you set up your Waineo test, fabricated your light source, etc.

Your first hand experience in its use would be invaluable shared amongst us.

I couldn't find any such information via the search function.  Thanks.  Gil




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