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Making and Using a "Monocentric" Eyepiece from Commercial Parts

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#1 SandyHouTex

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Posted 10 September 2014 - 07:45 PM

So a while back I decided to make my own "Monocentric" eyepiece using commercial parts to see what all the hubbub was about.

 

The TMB "Monocentrics", both the old ones and the new "Super Monocentrics" sold by APM are pretty pricey at $500 per eyepiece.  In addition, the used Zeiss "Monocentrics", command prices of $1000.  So I was anxious to see what the deal was.

 

You may be wondering at this point why I keep putting "Monocentric" in quotes.  That would be because none of the TMBs, old or new, or the Zeiss is a "Monocentric" eyepiece.  At their heart is a Hastings triplet.  Hasting's triplets are used in high end magnifiers because they have probably the best optical properties of a triplet, save for a true Monocentric.  Monocentric means "one center", and on the true Monocentric design all of the elements have a common center.  A Hasting's triplet does not. 

 

So if you want to put one together to see what kind of performance you will get, before plunking down your hard earned cash for a TMB or Zeiss:

 

Here's the $40 c-mount adapter for the lens:

http://www.edmundopt...ns-mounts/54621

 

Here's the $95 Hastings triplet lens:

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

 

And here's the $36 1 inch to 1 1/4 inch adapter:

http://www.highpoint...nosepiece-cnose

 

Put the lens in the c-mount and secure, then screw the c-mount on to the adapter.  Viola, you have you're very own  10 mm. "Monocentric" eyepiece.

 

Some comments on it.  It has a MagF coating on it and reduces or eliminates "pincushion distortion", spherical and chromatic aberrations.

 

What I've seen in use is that it is very sharp in the center but has significant field curvature, thus it gets blurry near the edge of a very small 30 degree field of view.  Planetary and star colors are nicely saturated.  But in the end, my BGOs and Brandons are just as good.  So I'll let others decide of the commercially and, in the case of the Zeiss, used "Monocentrics" are worth the price.  For me they are not.

 

Clear skies and Have Fun,


Edited by RodgerHouTex, 10 September 2014 - 08:15 PM.


#2 SteveC

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Posted 10 September 2014 - 08:04 PM

Oh, you didn't try the Steinheil triplet. I think you missed the boat in that case. That was the one to get, not the Hastings!!



#3 SteveC

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Posted 10 September 2014 - 08:11 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.



#4 SandyHouTex

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Posted 10 September 2014 - 08:24 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.


Edited by RodgerHouTex, 10 September 2014 - 08:31 PM.


#5 SteveC

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Posted 10 September 2014 - 08:51 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.

 

You may be right about the Edmund Hastings, I've never tried using one, though I believe I remember a conversation with someone who has.



#6 mgwhittle

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Posted 10 September 2014 - 09:14 PM

So based on your experience, if you have a Brandon there is no improvement in the image using the "monocentric" you made?  Am I reading that correctly?



#7 jtaylor996

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Posted 10 September 2014 - 09:33 PM

Rodger, what you made has little to do with a real supermono. The glasses are probably all wrong, the polish and assembly/alignment is going to suck. The coatings won't be even close, either. 

 

The TMBs were made by berliner glass, one of the zeiss suppliers. So I expect the level of polish on a TMB is identical to the zeiss. If you want a comparison , just borrow a real one before deciding to dismiss super high quality orthos just because your homemade version turned out crappy. 


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#8 Jeff Morgan

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Posted 10 September 2014 - 10:29 PM

Rodger, what you made has little to do with a real supermono. The glasses are probably all wrong, the polish and assembly/alignment is going to suck. The coatings won't be even close, either. 

 

The TMBs were made by berliner glass, one of the zeiss suppliers. So I expect the level of polish on a TMB is identical to the zeiss. If you want a comparison , just borrow a real one before deciding to dismiss super high quality orthos just because your homemade version turned out ****. 

 

About as likely as my old Jaegers 38mm Tank Periscope eyepiece telling me a lot about my Panoptics.

 

Or a Kia telling me a lot about a Mercedes Benz. Whether or not I find a value proposition in the Benz, the Kia will tell me nothing substantial about it. Two separate issues entirely.

 

BTW - As much as I love my Brandons (own the anniversary set plus the 48mm), they are being outpaced by my TMB Supermonos and Astro-Physics SPL's using a 120mm f/8.5 apochromat.



#9 Alan A.

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Posted 11 September 2014 - 12:54 AM

Great project Rodger. Thanks for sharing how you built it, I have not used a c mount before.

I have been building ball, Galilean, Keplerian and some doublet lens eyepieces. Mostly using Edmund Optics lenses and Surplus Shed parts for housings. All excellent fun!

#10 BillP

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Posted 11 September 2014 - 08:26 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.

 

 

Naming of a lens set or eyepiece has little to do with its actual optical design.  So everyone can make the curves a little different depending on their goals, and the curves can be at varying precision.  So you really can't make a judgement of which might be better or worse, optically or otherwise, by the naming of the item.  You would need either the exact optical prescription used, or a bench test, or a field test.  Only way to make a judgement based on name, is if the eyepiece follows the exact patent prescription for that design. 

 

Btw, I think many will argue that level of polish is critically important to the performance.  FWIW, I've tested the Zeiss monos against a variety of Abbes and TMB Supermonos and premium Plossls.  It's on-axis image was by far in a different league and readily apparent in the field tests.

 

FWIW, In some old forum posts, Tom Back said the following regarding what would be the *best* planetary *eyepiece design*: "The triplet cemented Steinheil Monocentric, with the two outer surfaces multicoated with either the Zeiss T-coat, or the Pentax SMC multicoat."  Markus, RC, and others participated and none of them disagreed.  https://groups.googl...eur/zahPPDK9kG0



#11 BillP

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Posted 11 September 2014 - 08:34 AM

Btw, Siebert Optics makes a MonoCentric I.D. eyepiece for about $200.  Avalibale in 10mm and longer focal lengths.  I tested them out.  Typical of cemented triplets in that only central portion of FOV is sharp in fast scopes.  Worked fairly well in F8s, like Supermonos.  I put them at about the planetary performance of an AP-SPL, or just shy of that.  So not bad at all.  Construction is the typical utiliarian though, so not that refined.



#12 jtaylor996

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Posted 11 September 2014 - 08:43 AM

Bill, I was about to suggest those last night, but I haven't personally used them. Does Siebert use any known coatings on his stuff?



#13 Sean Cunneen

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Posted 11 September 2014 - 12:51 PM

I made a couple of monocentric eyepieces last winter from Surplus Shed optics. The glass ended up being from Rolyn Optics, and was a 20mm fl. coated Steinheil triplet. I was able to pull out the E and F stars of the trapezium no problem, so it was quite a performer in my f15 refractor but suffered terribly in my faster scopes. Charles Hastings was an ATM and modified the Steinheil triplet to make what he considered the superior planetary optic of his day. Don't be put off by the fact that they are used as magnifiers/loupes! The downside is the FOV and if your field stop is too large, really bad things happen...



#14 BillP

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Posted 11 September 2014 - 03:09 PM

Bill, I was about to suggest those last night, but I haven't personally used them. Does Siebert use any known coatings on his stuff?

 

 

He says they are multicoated when they are.  His Barlows hae excellent coatings.  But I don't know where he gets the lenses.  Some think he sources them from Edmund.

 

My impressions - http://www.cloudynig...monocentric-id/


Edited by BillP, 11 September 2014 - 03:11 PM.


#15 SandyHouTex

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Posted 11 September 2014 - 03:58 PM

Rodger, what you made has little to do with a real supermono. The glasses are probably all wrong, the polish and assembly/alignment is going to suck. The coatings won't be even close, either. 

 

The TMBs were made by berliner glass, one of the zeiss suppliers. So I expect the level of polish on a TMB is identical to the zeiss. If you want a comparison , just borrow a real one before deciding to dismiss super high quality orthos just because your homemade version turned out ****. 

 

Sounds like a lot of speculation.  And I didn't say my "Monocentric" turned out poorly.  It's very sharp on axis, it has severe curvature of field, and a small field of view just like has been documented with the TMBs and the Zeiss.  I personally don't like the small field of view and field curvature, therefore I can't see me buying a commercially made one for three to seven times the price.

 

With a triplet, which is what I built, and what the TMBs and Zeiss are, it is hard to correct that many aberrations.  See the thread currently active called "Good Kellners".  Polish only corrects scatter not aberrations.

 

The comment about the glass being all wrong is also speculation.  I'm not aware of any source that has identified the glasses used in the TMBs or the Zeiss.  Also, I didn't buy the Hastings triplet from Joe's All Night Optical Warehouse down on the corner.  I got it from Edmund Optics which makes some very high quality - wait for it - optics.  The lenses were accurately centered, there was no bubbles in the glue joining the elements, the coatings were uniformly applied, etc., etc.

 

Here is an example of a TRUE Monocentric eyepiece which Chris Lord in "The Evolution of Eyepieces" says, "These are the most nearly perfect eyepieces ever designed, having highly corrected achromatic and orthoscopic fields, flat over the greater part, and very dark.

 

truemonocentric.jpg

 

Here are pictures of the Zeiss and TMBs:

 

Zeiss monocentric.jpg  TMB Super Monocentric.jpg

 

As you can see the TMBs and Zeiss are not Monocentrics (meaning all one center, which is what the curves of the optical elements in the Monocentric have) but triplets.  The best corrected triplet currently available is the Hastings, hence my choice.

 

I would suggest that if someone is as curious as I am, make the "Monocentric" eyepiece I describe and compare it to the new TMB "Super Monocentric", or a Zeiss "Monocentric" and tell us the results.  I think if the results were reported in an unbiased manner, they might be surprising.


Edited by RodgerHouTex, 11 September 2014 - 04:11 PM.


#16 fjs

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Posted 11 September 2014 - 04:08 PM

Hi Rodger,

 

Sorry if I'm :beat: .

 

Would you clarify your comment about your "BGOs and Brandons are just as good"?

 

I am guessing you mean overall. But maybe not necessarily on axis?

 

Thanks.



#17 SandyHouTex

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Posted 11 September 2014 - 04:18 PM

Hi Rodger,

 

Sorry if I'm :beat: .

 

Would you clarify your comment about your "BGOs and Brandons are just as good"?

 

I am guessing you mean overall. But maybe not necessarily on axis?

 

Thanks.

 

Sure, no problem.  The BGOs and the Brandons are my go to eyepieces.  Overall I think they are better because they are orthoscopic, meaning no or little distortion, have a wider field of view than the "Monocentric" I made, and don't show anywhere near the field curvature.  There might have been slightly more detail on Saturn when looking on axis at it with the homemade "Monocentric", but for the other reasons, I just find the BGOs and Brandons so much easier to use.  Particularly, I like orthos and Brandons and even some Symmetricals (wrongly called Plossls) with their 40 deg. fields of view, but the 30 deg. field of view of the "Monocentric" plus the field curvature making it even smaller due to blurring was very uncomfortable for me.



#18 fjs

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Posted 11 September 2014 - 04:26 PM

:thanx:

 

Frank



#19 stevep

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Posted 11 September 2014 - 06:36 PM

Charles Hastings was an ATM and modified the Steinheil triplet to make what he considered the superior planetary optic of his day.

 

This is wrong, the Hastings triplet is not a modified Steinheil, it's a completly different design, the Hastings is a modified version

of a patented Zeiss design,

 

Steve



#20 BillP

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Posted 11 September 2014 - 07:03 PM

I would suggest that if someone is as curious as I am, make the "Monocentric" eyepiece I describe and compare it to the new TMB "Super Monocentric", or a Zeiss "Monocentric" and tell us the results.  I think if the results were reported in an unbiased manner, they might be surprising.

 

 

Actually, monocentrics do not have to look like the pictured one at all.  All that a monocentric is, is one where the radii of all the curves of all the lens surfaces have a common central point.  So draw any three concentric circles with the same center point, then slice a cylindrical section out of it, and you have a monocentric design.  FWIW, I've seen lots of pictures that are incorrect, even in patent documents.  The drawings are illustrative only, the definition of the curves and glass types and indexes of refraction and spacings are definitive.  So just saying be careful about drawing any conclusions from any sketched representation.

 

Also, it is typical for monocentric designs to be highly curved and not flat.  Various aberrations are also present.  To give you an example, here's a quote from a research project where they used monocentric lenses for a 40 gigapixel imaging systems.  Here's what the researchers say about the monocentric design...

 

"The described monocentric objectives consist of a
spherical core of a crown glass (low index and high
Abbe number) surrounded by meniscus shells of flint
glasses (high index and low Abbe number) with the
shell surfaces concentric with the spherical core center.
A stop is placed at the center of curvature to limit
the f =#. Excluding the vignetting caused by the stop,
the lens is symmetric with the respective incoming
field angle. Unlike an ordinary lens,monocentric systems
have no tightly defined optical axis. This means
that no off-axis aberrations, e.g., lateral chromatic
aberration, astigmatism, or coma, are present. The
only aberrations present are axial chromatic aberration,
spherical aberration, and spherochromatism. In
addition, the image has field curvature because it is
formed on a spherical surface also concentric with
the core
.
"

 

To have a superb eyepiece really means a lot more than simply design.  IMO the engineering execution is more critical.  Who cares how well the paper design is if there is a lot of internal reflections, if the coatings are applied non-optimally causing ghosting and more scatter, and if the polish is typical meaning a fair amount of more scatter robbing contrast and degrading sharpness.  The Zeiss Abbe execution visually is the best I've encountered other than the Zeiss Monos.  Lowest scatter and highest definition of any eyepieces I have come across.  Superbly executed engineering.

 

FWIW, there is one view that I have seen that is better....but it was a 10 degree AFOV in the center of a spherical singlet "ball" eyepiece.  It was also a high specification lens so curves very precisely ground and polished.  No back scatter of course since only one lens so light had nothing to bounce around off of to come back to the optical axis.  Multi-element lenses, even cemented monocentrics will have backscatter between the lenses.  Single coating also helped keep scatter at absolute minimum since no multi-layers which can increase scatter if not executed very precisely. 


Edited by BillP, 11 September 2014 - 07:08 PM.

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#21 SteveC

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Posted 11 September 2014 - 09:01 PM

Btw, I misspelled monocentric on my tablet today, and it came out as mojocentric. I decided, that I liked the new spelling, so I'll probably spell it that way occasionally. I think the eyepiece is that special - Supermojocentric Eyepieces!!, that's the ticket.



#22 leonard

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Posted 12 September 2014 - 12:51 AM

Supermojocentric , :crazyeyes:   Wow that does have a certain ring to it .

 

         Maybe Siebert should .................

 

 

 

                                                        Leonard



#23 DaveJ

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Posted 12 September 2014 - 08:01 AM

Btw, I misspelled monocentric on my tablet today, and it came out as mojocentric. I decided, that I liked the new spelling, so I'll probably spell it that way occasionally. I think the eyepiece is that special - Supermojocentric Eyepieces!!, that's the ticket.

 

Here's a song title directed at RodgerHouTex: "Got my Supermojocentric workin' but it just don't work on you"


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#24 BillP

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Posted 12 September 2014 - 08:28 AM

The Mojocentrics are my favorite eyepieces by far!!



#25 Sarkikos

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Posted 12 September 2014 - 08:41 AM

 

FWIW, there is one view that I have seen that is better....but it was a 10 degree AFOV in the center of a spherical singlet "ball" eyepiece.  It was also a high specification lens so curves very precisely ground and polished.  No back scatter of course since only one lens so light had nothing to bounce around off of to come back to the optical axis.  Multi-element lenses, even cemented monocentrics will have backscatter between the lenses.  Single coating also helped keep scatter at absolute minimum since no multi-layers which can increase scatter if not executed very precisely. 

 

 

During the wild days of the ball eyepieces here on CN, I made a 5.8mm focal length ball eyepiece from an Edmund lens bought off eBay and the eyepiece barrel and housing from an old Huygens ... or was that a Ramsden or Kellner?  Only 10 deg on-axis is sharp within its 55 degree AFOV.  It was a disaster in any telescope that does not have a mount that tracks.  Now that I have a NexStar mount, I need to remember to take it out again for another trial.

 

Maybe it will show me the orographic clouds next Mars apparition through my C80ED.

 

Mike


Edited by Sarkikos, 12 September 2014 - 08:45 AM.



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