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Level of Eyepiece Polish

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#1 Kent10

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Posted 22 February 2019 - 02:11 AM

Is there a point at which an eyepiece doesn't benefit from any more polish?  It is "well-known" that Zeiss polished their ZAOs more than most other eyepieces, also Brandon and Clave, and that these eyepieces have lower scatter because of their high polish. 

 

Could Zeiss continue to polish even more for an even better eyepiece and would anyone notice the difference?  I read in one thread about Zeiss monocentrics made for professional observatories that were polished twice that of the already highly polished monocentrics made for amateurs.  See post #32 in this thread https://www.cloudyni...s-monocentrics/

 

If polish is so important for the quality of an eyepiece why don't more manufacturers polish more?  Time consuming I know but wouldn't this be done by a machine?  I guess even then that means fewer eyepieces are made.  How long does it take to polish an eyepiece to Zeiss standards?

 

I have seen Roland Christen's post on the subject.

 

"1. Polish for twice as long, minimum, as it takes to get the grey out, that is the rule of thumb in the industry for a good deep polish. This is the Zeiss standard, and they don't deviate from it. Take twice as long, costs twice as much. You can see where it is possible to shave off some cost. A
manufacturer will say, lessee if they'll notice if we only go 50% longer? NA! They'll never know the difference. Lessee if they will notice if we only go 25% as long? NA! they'll never see the difference. Lessee if ... etc. No, they'll never see the difference, BUT you will be celebrated all day long and praised for offering the eyepiece for LESS MONEY, right?

 

Is it necessary to polish for twice as long? The answer is yes, since below the fine ground surface is a thin layer of subsurface damage that cannot be seen, but shows up later after the glass undergoes the coating process where it gets heated to 600 DegF. It puts ever so slight haze into the optical path."

 

Thanks, Kent


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#2 ngc7319_20

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Posted 22 February 2019 - 08:09 AM

I was inspired by your post to go and test my eyepieces.  Could I really tell that Zeiss / Clave / Brandon had much lower scatter than others?  I gave them a light cleaning, shined a red laser through them, and tried to judge the scattering.   And the answer is...  No... I can't really tell much difference.  So would polishing for even longer make much difference?  I suspect not.

 

Pictures show a red laser shining up through the eyepiece from below.  All pics have same exposure. 

University Optics 25 Ortho seemed to be among the least scattering:

 

IMG_5488 UO25 1sec.jpg

 

TeleVue 25 Plossl not bad either:

 

IMG_5482 TV25PL 1sec.jpg

 

An old Celestron Ultima 24mm:

 

IMG_5476 Ultima24 1sec.jpg


Edited by ngc7319_20, 22 February 2019 - 08:12 AM.


#3 ngc7319_20

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Posted 22 February 2019 - 08:09 AM

Zeiss Abbe Ortho 25... Really nice eyepiece, but I'm not sure I'd say scattering was remarkably less than others...

 

IMG_5472 ZAO25 1sec.jpg

 

Finally an old ProOptic 25 Plossl... Probably the most scatter....

 

IMG_5485 ProOptic25 1sec.jpg

 

Others like Brandon and Clave were in the middle somewhere....


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#4 Kent10

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Posted 22 February 2019 - 08:55 AM

Thanks for your tests, ngc7319_20.  Interesting to see. 

 

I have compared scatter on many of my eyepieces and I see obvious differences in my Tec 180FL.  It can depend on the sky conditions to some extent but on some nights Zeiss Monocentrics seem to have the lowest scatter.  Also the Pentax orthos have low scatter and are enjoyed on brighter double stars.  TMB Supermonocentrics are again great for scatter control but they have more scatter than I expect for a 3 element eyepiece and I have always wondered if that is because they are brighter with only 3 lenses and the coatings that are used.  They do show more stars to me over some of my other eyepieces and seem slightly brighter.  The ZAOs and AP SPL again are really nice in the scatter control department.  There do seem like differences among all these eyepieces.  In some the scatter area is smaller and in some it might be larger but it is not as bright.

 

I have also compared the above eyepieces with my wider FOV and more elements eyepieces and the fewer element eyepieces have obviously better scatter control.  So much so that I don’t generally enjoy viewing brighter double stars with them.  I like them for their wide FOV but not for scatter control.

 

I have made quite a few comparisons with these eyepieces but I am still learning about them and continue to enjoy comparing them.  Sometimes my eye floaters get in the way and cause scatter so it can be difficult.  Lots of fun though.



#5 ngc7319_20

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Posted 22 February 2019 - 09:15 AM

Thanks for your tests, ngc7319_20.  Interesting to see. 

 

I have compared scatter on many of my eyepieces and I see obvious differences in my Tec 180FL.  It can depend on the sky conditions to some extent but on some nights Zeiss Monocentrics seem to have the lowest scatter.  Also the Pentax orthos have low scatter and are enjoyed on brighter double stars.  TMB Supermonocentrics are again great for scatter control but they have more scatter than I expect for a 3 element eyepiece and I have always wondered if that is because they are brighter with only 3 lenses and the coatings that are used.  They do show more stars to me over some of my other eyepieces and seem slightly brighter.  The ZAOs and AP SPL again are really nice in the scatter control department.  There do seem like differences among all these eyepieces.  In some the scatter area is smaller and in some it might be larger but it is not as bright.

 

I have also compared the above eyepieces with my wider FOV and more elements eyepieces and the fewer element eyepieces have obviously better scatter control.  So much so that I don’t generally enjoy viewing brighter double stars with them.  I like them for their wide FOV but not for scatter control.

 

I have made quite a few comparisons with these eyepieces but I am still learning about them and continue to enjoy comparing them.  Sometimes my eye floaters get in the way and cause scatter so it can be difficult.  Lots of fun though.

I suspect scattering is a complex question.  Lens polish is one factor.  But coatings with low reflectivity and low "roughness" are also important.  Fewer elements will help.  Blackened lens edges help.  Baffles and blackening in the eyepiece will help.   Perhaps even having a smaller field of view helps -- letting less light in to be scattered around. 

 

Yes, floaters and "stuff" in and on the eyeball is another factor -- I'm not sure how one optimizes those.  You can hold an eyepiece up to a very bright distant point source of light and see all the defects and scattering sites inside and on the eyepiece lenses.  But you also see all the eye defects, and quickly realize the vast majority of the defects are in the eye and not the eyepiece.  Hmmm...


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#6 Kent10

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Posted 22 February 2019 - 09:19 AM

I suspect scattering is a complex question.  Lens polish is one factor.  But coatings with low reflectivity and low "roughness" are also important.  Fewer elements will help.  Blackened lens edges help.  Baffles and blackening in the eyepiece will help.   Perhaps even having a smaller field of view helps -- letting less light in to be scattered around. 

 

Yes, floaters and "stuff" in and on the eyeball is another factor -- I'm not sure how one optimizes those.  You can hold an eyepiece up to a very bright distant point source of light and see all the defects and scattering sites inside and on the eyepiece lenses.  But you also see all the eye defects, and quickly realize the vast majority of the defects are in the eye and not the eyepiece.  Hmmm...

Yes!  The reason for scatter is difficult to determine.  Also transmission.  That has always intrigued me.



#7 Paul G

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Posted 22 February 2019 - 10:21 AM

Yes!  The reason for scatter is difficult to determine.  Also transmission.  That has always intrigued me.

Transmission is easy, it can be measured.



#8 Kent10

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Posted 22 February 2019 - 10:34 AM

Transmission is easy, it can be measured.

Very true.  I suppose what intrigues me is figuring out why some eyepieces are brighter than other eyepieces when the difference in a measured transmission might only be a few % and supposedly shouldn't be noticed by a normal person's eye.  There are many other contributing factors that go into why I see more stars with my TMB SMC, for example.



#9 garret

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Posted 22 February 2019 - 02:48 PM

 

Very true.  I suppose what intrigues me is figuring out why some eyepieces are brighter than other eyepieces when the difference in a measured transmission might only be a few % and supposedly shouldn't be noticed by a normal person's eye.  There are many other contributing factors that go into why I see more stars with my TMB SMC, for example.

If one eyepiece has the best transmission in the yellow/ green spectrum it appears brighter then a ep with the best transmission in the red spectrum... yet both ep may have has the same average transmission, but also a blue tinted ep appears brighter then a red/ warm tinted ep.

 

Garrett van der Veen



#10 AxelB

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Posted 22 February 2019 - 02:59 PM

...

Yes, floaters and "stuff" in and on the eyeball is another factor -- I'm not sure how one optimizes those.

....

By using a bigger scope that will yield a larger exit pupil for the same given magnification, you can mitigate the effect of floaters.

The problem is floaters tends to come with old age, which is often not compatible with the use if larger and heavier instruments.... life’s a bich!

Edited by AxelB, 22 February 2019 - 03:00 PM.


#11 Jeff Morgan

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Posted 22 February 2019 - 03:20 PM

If polish is so important for the quality of an eyepiece why don't more manufacturers polish more?  Time consuming I know but wouldn't this be done by a machine?  I guess even then that means fewer eyepieces are made.  

Just because the polishing work is "only" done by a machine does not mean it is free.

 

Machines depreciate in an accounting sense, and wear with use in a physical sense. So in effect, machines get paid by the hour just as optical workers do. Twice the time = twice the cost component.

 

And even for someone who insists on believing Unicorn fantasies like machine work is free, you touch on another economic fact of life that should get through to them. Twice the time = less eyepieces made = less eyepieces to sell.


Edited by Jeff Morgan, 22 February 2019 - 03:20 PM.

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#12 MitchAlsup

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Posted 22 February 2019 - 04:42 PM

Is there a point at which an eyepiece doesn't benefit from any more polish? 

Yes, when the surface reached a black polish that surface does not benefit from any more polishing.

A black polish has a 0-0 scratch and dig specification, you cannot find a single scratch or a single remaining pit when examined by a microscope.

 

Nobody can afford this kind of polish except

a) coronagraphs where several lenses have to have this quality level to even function. A coronagraph is trying to observe something that is 1 million times dimmer than a nearly object, so any scatter from the object will completely eliminate the ability to observed the dim thing right besides the bright thing.

b) amateur made lenses when the glass pusher does not care about the passing of time.



#13 precaud

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Posted 22 February 2019 - 05:43 PM

I was inspired by your post to go and test my eyepieces.

[snip]

Pictures show a red laser shining up through the eyepiece from below.  All pics have same exposure. 

 

There have been threads on this test, and the general consensus is, what it being seen is not related to the surface scatter, but to the lens ensemble geometries.

I did my own series of similar tests and I saw no correlation with eyepieces that had less scatter visually.


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#14 Starman1

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Posted 22 February 2019 - 05:57 PM

What John says is true.  Different eyepieces have internal elements that focus at different distances.

If an element projects an out-of focus dot, it may seem to have more scatter, but this may not occur on a star at infinity.


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#15 MartinPond

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Posted 22 February 2019 - 09:02 PM

I can qualitatively evaluate the whole effect by 

illuminating a target to super-brightness and exploding the image with

a 6x18 monocular.   Edges and bright parts develop a finely-sandblasted look

or a very smooth look.    The effect on resolution and apparent contrast is

due to that, not really to gross-scale scattering....that fogs the whole view.

 

In low or moderate coast eyepieces, the 'sandblasting' generally shows up much

more at short focal lengths than at long ones.  This is yet another reason why,

for example, a 25mm Meade 4000 -Plossl in a 2x Barlow can give a more detailed

and intense view  than a 12.4mm 4000  alone.  

If you polish long-fl and short-fl elements to the same standard, the short-fl will

have more 'speckling', that is, very slight deviations from the ideal.

Mostly it's a faceting around digs you have polished out.

 

Old "sleeve-burned" binocular eyepieces can have their sharpness radically improved

with a wet thumb, Bon-Ami, and 5 minutes gentle buffing, even though what's left of the

coating is wiped out.    

 

The EPs from  Zeiss 6x30 Silvarems, circa 1932,  have amazingly smooth fine detail.

Obsessive polishing and obsessive baffling have always been among their tickets

to the top teir.  And...it definitely takes longer.

 

Still, the way they mass-produce lenses now does do a very good job.. 


Edited by MartinPond, 22 February 2019 - 09:06 PM.


#16 agmoonsolns

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Posted 22 February 2019 - 09:06 PM

What's your opinion of the optics from Leica/Leitz? How would you rate their quality of finish and resulting light scattering? Are they as good as the eyepieces from Zeiss?



#17 SomebodyElseEntirely

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Posted 23 February 2019 - 01:15 AM

What's your opinion of the optics from Leica/Leitz? How would you rate their quality of finish and resulting light scattering? Are they as good as the eyepieces from Zeiss?

I think it is difficult to generalise because few of us have made extensive comparisons across the range of eyepieces offered by these companies.

 

In my case, I have a number of older, pre-globalisation eyepieces (military and microscope units) from the likes of Leitz and Wild-Heerbrugg. But I have only one modern Leica eyepiece (Chinese-made, of course). I could tell you how that compares to a German-made Zeiss eyepiece of identical specs. It’s just a single example, but if you think it might be of interest, let me know and I’ll write up some info.



#18 agmoonsolns

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Posted 23 February 2019 - 01:20 AM

Yes, that would be very interesting. Also, if anyone here has compared the Leica zoom to the Baader zoom as far as surface smoothness and light scatter.



#19 Kent10

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Posted 23 February 2019 - 01:26 AM

What's your opinion of the optics from Leica/Leitz? How would you rate their quality of finish and resulting light scattering? Are they as good as the eyepieces from Zeiss?

I am not sure who you were asking, but I have the Leitz 30mm 88 degree eyepiece and really like it.  I haven't, however, made extensive comparisons except with the 31mm Nagler as many others have.  Some like the Leitz more and others like the Nagler more.  I think the Nagler has less field curvature and is sharper at the edge.  But I like the comfort and sharpness on axis of the Leitz.  There is also something about the color of the stars and the presentation I like better in the Leitz.  I don't know if this is less scatter or what.  I do enjoy the Nagler sometimes on large star fields such as M24 but overall I like the Leitz more and I don't think it is because I spent so much for it smile.gif.

 

I also have the Leica Zoom.  I think the scatter is controlled well but I haven't made any comparisons lately.  I do enjoy the views and of course it zooms.  What I don't like is the EOFB (Edge of Field Brightening) that many of us see with the eyepiece and it is not as comfortable for me as others at all focal lengths.  I use it from time to time and do like it.



#20 Kent10

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Posted 23 February 2019 - 01:30 AM

Yes, that would be very interesting. Also, if anyone here has compared the Leica zoom to the Baader zoom as far as surface smoothness and light scatter.

I do not have experience with the Baader Zoom so what I say is only from what I have read on this forum.  I know many really like the Baader but I don't recall anyone who would say the Baader is better than the Leica.  It might be better is some ways such as its zoom range is larger and perhaps it doesn't have the EOFB.  But for scatter and sharpness I would bet the Leica easily beats the Baader.  Leica is much more expensive of course.



#21 Kent10

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Posted 23 February 2019 - 01:33 AM

Yes, when the surface reached a black polish that surface does not benefit from any more polishing.

A black polish has a 0-0 scratch and dig specification, you cannot find a single scratch or a single remaining pit when examined by a microscope.

 

Nobody can afford this kind of polish except

a) coronagraphs where several lenses have to have this quality level to even function. A coronagraph is trying to observe something that is 1 million times dimmer than a nearly object, so any scatter from the object will completely eliminate the ability to observed the dim thing right besides the bright thing.

b) amateur made lenses when the glass pusher does not care about the passing of time.

Thanks.  The 0-0 scratch/dig must be very difficult to attain.  Tonight I was reading about 10-5 I believe but that is as good as I have seen.  https://www.newport....ptical-surfaces  I wonder what the ZAOs are and how much, if at all, it varies from eyepiece to eyepiece.



#22 Kent10

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Posted 23 February 2019 - 01:41 AM

If one eyepiece has the best transmission in the yellow/ green spectrum it appears brighter then a ep with the best transmission in the red spectrum... yet both ep may have has the same average transmission, but also a blue tinted ep appears brighter then a red/ warm tinted ep.

 

Garrett van der Veen

Interesting.  Thanks.



#23 Kent10

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Posted 23 February 2019 - 01:42 AM

By using a bigger scope that will yield a larger exit pupil for the same given magnification, you can mitigate the effect of floaters.

The problem is floaters tends to come with old age, which is often not compatible with the use if larger and heavier instruments.... life’s a bich!

Right!  A binoviewer can help, too.



#24 garret

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Posted 23 February 2019 - 02:24 AM

 

The 0-0 scratch/dig must be very difficult to attain.  Tonight I was reading about 10-5 I believe but that is as good as I have seen.  https://www.newport....ptical-surfaces  I wonder what the ZAOs are and how much, if at all, it varies from eyepiece to eyepiece.

Mirrors with 0-0 scratch/ dig are available from stock: https://www.newport....ce-supermirrors

Notice these mirrors have 99.97% reflectivity; a smooth optical surface enhance optical performance.

 

Likely the smoothest optical surface in the world are the mirrors in the very long base LIGO interferometer, they are also ultra high reflective: they absorb only one photon out of every 3.3milion photons.

Source: https://www.ligo.cal...edu/page/optics

 

Garrett van der Veen



#25 leonard

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Posted 23 February 2019 - 02:47 AM

Mirrors with 0-0 scratch/ dig are available from stock: https://www.newport....ce-supermirrors

Notice these mirrors have 99.97% reflectivity; a smooth optical surface enhance optical performance.

 

Hello ,

 

            I read that and saw the specification sheet says scratch/dig 20-10 am I missing something ?




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