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Making and Using a "Monocentric" Eyepiece from Commercial Parts

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#51 BillP

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Posted 14 September 2014 - 07:11 PM

FWIW, another monocentric design...  http://www.google.co...tents/US2604012

 

And another interesting page... http://www2.odn.ne.j...ocentric99.html


Edited by BillP, 14 September 2014 - 07:15 PM.


#52 stevep

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Posted 14 September 2014 - 07:18 PM

 

 

I'm still not sure I understand your reply post,

 

As said in my previous post ''they say'' is Steinheil, the designer and inventor of this eyepiece,

are you stating that the illustration in fig 6 is incorrect,

 

IE: that the design and the production eyepieces  did not look like this,

 

Steve

 

 

Let's see if I can do better...  I am not saying that the production and design did not look like this.  What I am saying is that the design picture of the monocentric, is not monocentric because the curves of the elements as pictured, do *not* follow the language they provide which says that it is: "Consisting of three cemented lenses...of which the radii are all struck from a common centre."  The picture is incorrect in that none of those elements show a common center of radii.  So it is not technically accurate and just for illustrative purposes only to give you a general idea and nothing more...it's a pretty picture and not an accurate and scaled representation of the device. That being the case, you really can't make any assumptions about the accuracy of the even the shapes of the lens elements A, B, and C.  Given that the curves do not even match the criteria, can't trust anything else.  In addition, shapes of the lenses, cylindrical or cone shaped, I'm sure are not necessary to be as shown.  Bottom line is that one really can't tell much of anything from a picture.  You need the glass types, the indexes of refraction, the curve radii, and the spacings.  Once you have all that, then you can begin to make some good deductions.

 

 

Let's forget about the picture, it's just an illustration, we all know that, I even said in an earlier post ''it's not an engineering drawing let alone an optical precription'' I don't even understand why you would bother to to take ''said illustration'' into Photoshop and produce that circle's image, Photoshop is just a pixel based editor, the illustration is just an illustration, nothing could be gained,

 

so let's accept the illustration is incorrect, and just take the description, are you stating that the Steinheil monocentric design is not monocentric ?,

 

Steve



#53 BillP

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Posted 14 September 2014 - 07:36 PM

... are you stating that the Steinheil monocentric design is not monocentric ?

 

 

To my knowledge I have made no claim that the Steinheil Mono is monocentric or that it is not.  My only stake in this discussion is that sketches of designs tell us nothing since they are not engineering diagrams to scale.  If all the spherical surfaces in the Steinheil Mono have the same radii, then it would fit the definition of being monocentric (i.e., with one center).  The sketch of the Steinheil Mono that you provided the link for is definitely not a monocentric since all the curves have different radii in the picture.


Edited by BillP, 14 September 2014 - 07:39 PM.


#54 Jeff Morgan

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Posted 14 September 2014 - 10:02 PM

 

 

Anyway, I wasn't asking you to do any destructive testing.  I know you frequently take eyepieces apart and I thought it would be cool to just open up the TMB you have and see what was inside.

 

 

OK Roger!  Do you know what a p.i.t.a. it is to futz with 4mm lens sets :bigshock:  Anyway, decided to give it a try for youall...OMG was it unnerving!

 

Anyway, attached is the pic.  The 4mm Supermono is all I have.  Interesting to note that the lenses are not blackened.  Also interesting to note, although not pictured, is that there was a mark on one side indicating the eye lens, so they obviously have an orientation (others have said they can be flipped and are omnidirectional).  So here is the pic.  Not sure if any conclusions can be drawn from this given can't see any curves between elements and have no idea of the glass types or indexes, all of which change what a design visually looks like,  It was a microscopic lens so had all kinds of extensions on my camera lens to get to this image scale.  Right side is the field lens.  The entire lens is about 1/10th" in diameter!!  Have fun :grin:

 

 

Bill, your courage is admirable, but you can rest easy.

 

A search of the TMB Optical Yahoo group for postings from Thomas Back will reveal that the TMB Supermono was designed to be easy (his words, not mine) to disassemble and clean by the end user. The hardest part of course is handling such small elements.

 

Orientation? Doesn't matter! The eye lens and field lens are effectively identical - in other words, you can put it together "backwards".

 

As far as the lens edges not being blackened - edge blackening is more marketing pap to fool the gullible into thinking their current eyepieces are giving them "contrast". The Astro-Physics SPL's also are not edge blackened. Those two brands are about the best in the business when it comes to contrast. If that doesn't tell the the buying public something, then they are a lost cause indeed.


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#55 BillP

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Posted 14 September 2014 - 11:51 PM

 

A search of the TMB Optical Yahoo group for postings from Thomas Back will reveal that the TMB Supermono was designed to be easy (his words, not mine) to disassemble and clean by the end user. The hardest part of course is handling such small elements.

 

Orientation? Doesn't matter! The eye lens and field lens are effectively identical - in other words, you can put it together "backwards".

 

As far as the lens edges not being blackened - edge blackening is more marketing pap to fool the gullible into thinking their current eyepieces are giving them "contrast". The Astro-Physics SPL's also are not edge blackened. Those two brands are about the best in the business when it comes to contrast. If that doesn't tell the the buying public something, then they are a lost cause indeed.

 

 

Yes...I recall that post.  Perhaps easy for Thomas...not so easy for me.  Issue was more re-assembly.  The tolerance was very tight so difficult getting the lens back into the slot.  The AP-SPL method was much better...having lens set in a removable assembly.

 

I also heard the orientation thing that it didn't matter.  Still, there was a decided marking on the lens edge of the eye lens.  Of no orientation issue, then why have the mark there?  Does make one wonder.

 

Edge blackening.  I hear you.  I have also blackened lenses on a number of EPs but hard to tell if any difference.  Still, there is an Edmund technical report that says that there is a level of scatter that can be measured from un-blackened sides.  So again...makes one wonder if it really is a marketing hype or not.  Of course, in a similar situation, a number of well respected premium EP makers also though multicoating more than just the eye lens, even on complex EPs, was nonsense.  Whether it has any impact or not, it would sure be more boring if there weren't these silly debates...to edge blacken or not....is or isn't high magnification empty...how many angels can dance on a pin, etc.   :lol:



#56 jtaylor996

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Posted 15 September 2014 - 01:06 PM

 

 

Anyway, I wasn't asking you to do any destructive testing.  I know you frequently take eyepieces apart and I thought it would be cool to just open up the TMB you have and see what was inside.

 

 

OK Roger!  Do you know what a p.i.t.a. it is to futz with 4mm lens sets :bigshock:  Anyway, decided to give it a try for youall...OMG was it unnerving!

 

Anyway, attached is the pic.  The 4mm Supermono is all I have.  Interesting to note that the lenses are not blackened.  Also interesting to note, although not pictured, is that there was a mark on one side indicating the eye lens, so they obviously have an orientation (others have said they can be flipped and are omnidirectional).  So here is the pic.  Not sure if any conclusions can be drawn from this given can't see any curves between elements and have no idea of the glass types or indexes, all of which change what a design visually looks like,  It was a microscopic lens so had all kinds of extensions on my camera lens to get to this image scale.  Right side is the field lens.  The entire lens is about 1/10th" in diameter!!  Have fun :grin:

 

 

My god, I can't believe you actually did that, and didn't die of a heart attack. Having one, I know it's about the size of the head of a pin. Well, I know not to buy any used EPs from Bill, now!



#57 stevep

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Posted 15 September 2014 - 02:24 PM

 

... are you stating that the Steinheil monocentric design is not monocentric ?

 

 

To my knowledge I have made no claim that the Steinheil Mono is monocentric or that it is not.  My only stake in this discussion is that sketches of designs tell us nothing since they are not engineering diagrams to scale.  If all the spherical surfaces in the Steinheil Mono have the same radii, then it would fit the definition of being monocentric (i.e., with one center).  The sketch of the Steinheil Mono that you provided the link for is definitely not a monocentric since all the curves have different radii in the picture.

 

 

Thanks Bill,

 

And I never meant it to seem like you had,

I was more interested on your thoughts and views on what seems a most unusal eyepiece design,

it's definetly part of history, and Steinheil was a very clever and interesting designer/inventor,

 

Steve



#58 BillP

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Posted 15 September 2014 - 03:37 PM

See Sention 8.5.5. here.  Talks about difference in Steinheil vs Zeiss mono briefly.  http://books.google....entric"&f=false



#59 desertlens

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Posted 15 September 2014 - 03:49 PM

There might be some access to equipment issues here but what about an industrial X-ray machine to save the tedium and risk of disassembly?



#60 SandyHouTex

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Posted 15 September 2014 - 03:52 PM

FWIW, another monocentric design...  http://www.google.co...tents/US2604012

 

And another interesting page... http://www2.odn.ne.j...ocentric99.html

 

The first article is great, I wonder if they ever made any of them.

 

The second, not so much.  Triplets where the lens radii centers are not located in the same place are not Monocentric (meaning one center).  A Hastings triplet is not a Monocentric, nor is a Steinheil triplet.

 

Geez.

 

And Jeff, if they can be assembled both ways than the lens elements must all be symmetric (R1 = R6, R2 = R5, and R3 = R4), and the eyepiece only has 2 glass types.  Just like a Hastings triplet.  Which was and is my original point.



#61 BillP

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Posted 15 September 2014 - 04:45 PM

 

And Jeff, if they can be assembled both ways than the lens elements must all be symmetric (R1 = R6, R2 = R5, and R3 = R4), and the eyepiece only has 2 glass types.  Just like a Hastings triplet.  Which was and is my original point.

 

 

Not necessarily IMO.  A monocentric can be symmetrical like the top one in my pic, and also like the bottom one in my pic, central one is an asymmetrical mono.  The bottom has common radii center on all surfaces, just did not use the full "ball" in the central element.  So this to me also fits the "monocentric" definition where all surfaces have a common radii center -- the physical center need not be common for it to be termed a monocentric IMO and still adhere to the monocentric spirit...or the designer could call it Supermonocentric if they wanted to differentiate it such when the common center is not physically located in the same spot. 

 

On the Hastings Triplet, the spheres on those surrounding meniscuses are not concentric as they would be when they are monocentric.  http://www.thorlabs....-AutoCADPDF.pdf

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Edited by BillP, 15 September 2014 - 04:58 PM.


#62 Jeff Morgan

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Posted 15 September 2014 - 11:01 PM

Yes...I recall that post.  Perhaps easy for Thomas...not so easy for me.  Issue was more re-assembly.  The tolerance was very tight so difficult getting the lens back into the slot.  The AP-SPL method was much better...having lens set in a removable assembly.

 

I also heard the orientation thing that it didn't matter.  Still, there was a decided marking on the lens edge of the eye lens.  Of no orientation issue, then why have the mark there?  Does make one wonder.

 

Edge blackening.  I hear you.  I have also blackened lenses on a number of EPs but hard to tell if any difference.  Still, there is an Edmund technical report that says that there is a level of scatter that can be measured from un-blackened sides.  So again...makes one wonder if it really is a marketing hype or not.  Of course, in a similar situation, a number of well respected premium EP makers also though multicoating more than just the eye lens, even on complex EPs, was nonsense.  Whether it has any impact or not, it would sure be more boring if there weren't these silly debates...to edge blacken or not....is or isn't high magnification empty...how many angels can dance on a pin, etc.   :lol:

 

 

:lol:  Yes, with my ten magical thumbs it would probably be hard for me too.

 

On the orientation and the marks - I can think of one other place those are used - ever take a refractor objective apart? You don't suppose they rotated the individual lenses before cementing them? 

 

Don't get me wrong on the edge blackening - its doesn't hurt anything (provided certain cleaning solvents like acetone don't migrate into the barrel). Maybe it even helps. In that light, I don't mind blackened edges. Blackened eyepieces I have owned (TeleVues for sure, perhaps a few others) were good performers. But the lowest scatter examples I have ever owned (SPLs and TMBs) are not edge blackened.



#63 jrbarnett

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Posted 15 September 2014 - 11:15 PM

 

Just kidding!  :grin:

 

I tried the Steinheil a couple of years ago. One time, and it hasn't left the closet since. These Edmund triplets are not comparable to any of the monocentrics, TMB or Zeiss, not even close.

 

Actually the Steinheils are optically inferior to the Hastings.  If I remember, the discussions are in the Edmund's catalog.  They make both.  The Steinheil is actually a relay lens.

 

I also disagree with your comment on the Edmund Hastings triplets.  I would expect that they are the equal of the TMBs but may not have the level of polish of the Zeiss.   But polish only affects scatter, it does nothing to improve the inherent aberrations in the design.  And, if the Zeiss is a Steinheil triplet which it may be, then the Edmund would be superior optically.

 

Edmund optics have standard consumer grade polish ratings (60/40 scratch-dig).  TMB and Zeiss both spec'ed considerably higher polish levels.  Polish is king on axis.  Edmund also uses simple AR coatings.  I wouldn't expect the Edmund-lensed Monos to be particularly good compared to other pedestrian eyepieces like the UO Volcano Top Orthos or even GSO Plossls, much less the premium Zeiss and TMB units.

 

You could always try a Siebert Monocentric.  I'm pretty sure Harry is using the Edmund lens groups.

 

- Jim



#64 BillP

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Posted 16 September 2014 - 07:40 AM

On the orientation and the marks - I can think of one other place those are used - ever take a refractor objective apart? You don't suppose they rotated the individual lenses before cementing them? 

 

Not in this case as the mark was not across the elements but only along the side of the eye lens element.  So given this I took it to be marking that particular element...and only reason I could think of was for assembly. But who knows.  I did not feel like putting it toether differently to see if it behaved differently since was having such a hard time getting back together. 



#65 SandyHouTex

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Posted 16 September 2014 - 10:02 AM

 

 

Just kidding!  :grin:

 

I tried the Steinheil a couple of years ago. One time, and it hasn't left the closet since. These Edmund triplets are not comparable to any of the monocentrics, TMB or Zeiss, not even close.

 

Actually the Steinheils are optically inferior to the Hastings.  If I remember, the discussions are in the Edmund's catalog.  They make both.  The Steinheil is actually a relay lens.

 

I also disagree with your comment on the Edmund Hastings triplets.  I would expect that they are the equal of the TMBs but may not have the level of polish of the Zeiss.   But polish only affects scatter, it does nothing to improve the inherent aberrations in the design.  And, if the Zeiss is a Steinheil triplet which it may be, then the Edmund would be superior optically.

 

Edmund optics have standard consumer grade polish ratings (60/40 scratch-dig).  TMB and Zeiss both spec'ed considerably higher polish levels.  Polish is king on axis.  Edmund also uses simple AR coatings.  I wouldn't expect the Edmund-lensed Monos to be particularly good compared to other pedestrian eyepieces like the UO Volcano Top Orthos or even GSO Plossls, much less the premium Zeiss and TMB units.

 

You could always try a Siebert Monocentric.  I'm pretty sure Harry is using the Edmund lens groups.

 

- Jim

 

 

Agree with you Jim on the level of polish.  However it should be noted that almost all amatuer astronomy eyepieces are a consumer grade polish.  Except of course the ones you mention, and my Brandons.   :lol:



#66 SandyHouTex

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Posted 16 September 2014 - 10:04 AM

 

 

And Jeff, if they can be assembled both ways than the lens elements must all be symmetric (R1 = R6, R2 = R5, and R3 = R4), and the eyepiece only has 2 glass types.  Just like a Hastings triplet.  Which was and is my original point.

 

 

Not necessarily IMO.  A monocentric can be symmetrical like the top one in my pic, and also like the bottom one in my pic, central one is an asymmetrical mono.  The bottom has common radii center on all surfaces, just did not use the full "ball" in the central element.  So this to me also fits the "monocentric" definition where all surfaces have a common radii center -- the physical center need not be common for it to be termed a monocentric IMO and still adhere to the monocentric spirit...or the designer could call it Supermonocentric if they wanted to differentiate it such when the common center is not physically located in the same spot. 

 

On the Hastings Triplet, the spheres on those surrounding meniscuses are not concentric as they would be when they are monocentric.  http://www.thorlabs....-AutoCADPDF.pdf

 

 

1 and 2 appear to be monocentric.  3 is not.  All radii on all elements must have one common center by definition.



#67 John Boudreau

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Posted 16 September 2014 - 07:07 PM

 

Edmund optics have standard consumer grade polish ratings (60/40 scratch-dig).  TMB and Zeiss both spec'ed considerably higher polish levels.  Polish is king on axis.  Edmund also uses simple AR coatings.  

 

 

 

 

 

 

 

Edmund does have 60/40 optics, in fact some filters are 80/50. But in this case, the Edmund Hastings triplet in question is spec'd at 40/20.

http://www.edmundopt...ic-lenses/67417



#68 SandyHouTex

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Posted 17 September 2014 - 10:33 AM

Thanks John.  Appreciate the clarification.

 

Also I did a little more research briefly last night and found this:

 

http://www.brayebroo...w_critique.html

 

It's Chris Lord's analysis of a report on a "certain, currently produced "Monocentric" eyepiece" review.  He states exactly what I posited at the beginning of this thread.  He says that the "certain, currently produced "Monocentric" eyepiece" is a derivitive of the Hastings triplet, not the Steinheil Monocentric design.  I know of know greater authority on the history of telescope eyepieces than Chris.  Search for and read his, "Evolution of Eyepieces" which is on his Braybrook Observatory website.  It's a fascinating read if you care about this sort of thing.

 

I also briefly looked at the section on Monocentric eyepieces in, "Telescopes, Eyepieces, and Astrographs" by Gregory Hallock Smith, Roger Ceragioli and Richard Berry, available from Willman-Bell publishers.  In chapter 17.5.1 it also talks about a "certain, currently produced "Monocentric" eyepiece" that is actually an asymmetric triplet with three glass types, which may be why BillP had a mark on the eye lens of his.  They also ray trace it.  The bad news, at f/5 the ON-AXIS spot plot is three times the diameter of the f/10 spot plot.  Unfortunately the authors don't have an Airy disk in the table but it probably affects the on-axis resolution.

 

I also read somewhere, I think in the review that Chris Lord's comments on above, that the contrast of the "certain, currently produced "Monocentric" eyepiece" may be only due to the 2 air/glass interfaces and the reduced reflection.

 

My $0.02.



#69 BillP

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Posted 17 September 2014 - 01:54 PM

1 and 2 appear to be monocentric.  3 is not.  All radii on all elements must have one common center by definition.

 

 

 

There is not much in a name.  So Zeiss modifies the Steinheil Monocentric and calls it a Hastings Triplet...TMB modifies a Steinheil Monocentric and called it a Super Monocentric...Everyone today modifies an Abbe by using modern glass types and calls them Abbe...Nagler modifies the Symmetrical Plossl and calls it a Plossl...etc.  Names and appearances of the lens set mean little to nothing really.  As RC posted once (paraphrased), an optical design is new and different if you deviate in any way from the original, which includes if you use a modern glass (e.g., think Baader Ortho).  If I were to invent my 3rd picture, I have the naming right, and given the inspiration was the Steinheil Monocentric, I would call it the Compressed Monocentric...so still a Mono, just a flavor  :grin:



#70 stevep

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Posted 17 September 2014 - 06:34 PM

 

1 and 2 appear to be monocentric.  3 is not.  All radii on all elements must have one common center by definition.

 

 

So Zeiss modifies the Steinheil Monocentric

 

 

I'd say Zeiss modified the Steinheil Triplet, the original design, the ''Steinheil Monocentric'' is a Unique design, no modifcations on this as a telescope eyepiece design as far as I am aware,

but your right, anybody can call anything what they like so long as it's different, I'm of to '' {]">?@#"^!'', (sleep)

 

Steve


Edited by stevep, 17 September 2014 - 06:55 PM.


#71 Jeff Morgan

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Posted 18 September 2014 - 01:47 AM

I'd say Zeiss modified the Steinheil Triplet, the original design, the ''Steinheil Monocentric'' is a Unique design, no modifcations on this as a telescope eyepiece design as far as I am aware,

but your right, anybody can call anything what they like so long as it's different, I'm of to '' {]">?@#"^!'', (sleep)

 

Steve

 

 

Well if you wake up still vexed by this, all you have to do is go the TMBOptical Yahoo Group. Do a search for posts by Thomas Back, body text "monocentric".

 

There is a wealth of information there to be data mined.

 

Since the original glasses and coatings used by Steinheil  were no longer available, Thomas Back used modern glasses and coatings to optimize a no-compromise planetary eyepiece.

 

And that is the important part.



#72 BillP

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Posted 18 September 2014 - 08:25 AM

I'd say Zeiss modified the Steinheil Triplet, the original design, the ''Steinheil Monocentric'' is a Unique design, no modifcations on this as a telescope eyepiece design as far as I am aware,

but your right, anybody can call anything what they like so long as it's different, I'm of to '' {]">?@#"^!'', (sleep)

 

Steve

 

 

I don't know...pretty difficult to be completely un-influenced.  As far as I'm concerned, the Steinheil Mono is simply a modification of a spherical singlet.  So who picked up the first sphere singlet and used it as an eyepiece?  The Steinheil Mono would be a modification of that.  Or he could have gotten the inspiration when examining a Hershel ball, or a Wallaston or Coddington. Everyone stands on someone elses shoulders and little that is actually unique.  Most everything is derived in one way or another.



#73 stevep

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Posted 18 September 2014 - 06:57 PM

Interesting view,

I agree that one idea and design is picked up by A.N. other and a new design/concept emerges, as someone said ''once the wheel was invented

the wheel barrow was not far behind'', as for Steinheil, well he developed the triplet and three years later the monocentric,

the triplet only had a fov of 20 degrees, he was an astronomer, the monocentric was an improvement giving a fov of approx 32 degrees and still

had all the quality's of the previous design, orthoscopic with no ghosts,

 

Steve



#74 stevep

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Posted 19 September 2014 - 07:56 PM

 

I'd say Zeiss modified the Steinheil Triplet, the original design, the ''Steinheil Monocentric'' is a Unique design, no modifcations on this as a telescope eyepiece design as far as I am aware,

but your right, anybody can call anything what they like so long as it's different, I'm of to '' {]">?@#"^!'', (sleep)

 

Steve

 


 

Since the original glasses and coatings used by Steinheil  were no longer available,

 

 

Unfortunately for Steinheil coatings had not been invented at the time these eyepieces were produced, the glass types were just common, this was the late 1800's, and the Mr Back's design is not based on the Steinheil monocentric design,



#75 Jeff Morgan

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Posted 20 September 2014 - 12:19 AM

 

Unfortunately for Steinheil coatings had not been invented at the time these eyepieces were produced, the glass types were just common, this was the late 1800's, and the Mr Back's design is not based on the Steinheil monocentric design,

 

 

Yes. See post #10986 on the TMBOptical User Group here:

 

https://groups.yahoo.../messages/10986




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