"Phase Compensation of Internal Reflection" by Paul Mauer, J. Opt. Soc. Am. 56, 1219 (1 Viewer)

Ed;

I should mention that I just bought the Barska a short time ago with a specific purpose in mind, for photos of some tests that may be posted and another project that I am working on that require a specific type of image. I did not expect it to be of the same quality of my usual boosters. I normally test with the best optic I have that gives me the magnification needed for the specific test under way.

I just did a quick star test of the Barska 10x40 monocular using the Promaster as the booster. I did try to photograph the results, but just to difficult to get everything lined up on a 500-micron exit pupil. I never did get an image on the camera.

The inside focus pattern was very impressive. Better than the Promaster. It showed very clean, perfectly circular diffraction rings (about 8 waves) with no discernable errors in lower order coma, alignment, astigmatism or pinch. The notable feature was a far brighter center ring than normal. Also, without the green filter in place there was a very bright, broad purple ring outside the outer diffraction ring indicating a high level of CA.

The in focus image was another story. There were three or four diffraction rings surrounded by a broad ring of cotton candy. The diffraction rings in the center were very bright. The cotton candy stuff was split into two hemispheres and judging by the angle of the split, may have been along the roof edge. The in focus image was observed at 80x.

The extra focal image was just a very bright center spot surrounded by a broad area of cotton candy.

My interpretation is that the Barska suffers mostly from higher order errors, mostly high order minus SA. My guess is that the higher order errors amount to about one wavelength. Kimmo or Henry may want to correct this assessment due to their high experience level and I would welcome that.

I have attached photos of the left tube Promaster tests with the Barska as the booster. Note the even light intensity across the patterns. Also note the in focus image. This was taken at about 240x magnification. The outside focus shows –SA of, maybe, 1/3 wavelength, part of which may be the 11 meter test length and since the in focus image was so good I think the test indicates less than 1/3 wave error and probably close to diffraction limited. Since I see –SA in most binoculars, I wonder if this is how the manufacturers add field curvature to control the rolling ball effect. Not being an optician, I have no idea how that is added.

BTW, what I term cotton candy is an indescribable indistinct image as shown in the Promaster extra focal image attached.

Alexis;

I think your points are very much on target and routinely overlooked. I just started star testing in the recent past but have found it to be an extremely reliable indicator of quality and easy to judge differences between units. So far all of my results have been confirmed by other measurements or visual perception in use. My experience is limited and Henry and Kimmo may weigh in, their experience level is vastly greater than mine.

As you suggested, when I started testing this way, I had the same concerns as Ed. I used several different boosters and tested several of my old reliable bins with 3 or 4 of them. My usual boosters are a 6x30 inverted image double collimator with fixed infinity focus of very good commercial test equipment quality and is my favored booster due to the 5 arc minute grid to measure apparent angle. My second best is the 8x20 Ultravid but not used often because of mounting. The other commonly used are an 8x20 Zeiss Monocular, a Zeiss 3x tripler and various commercial dioptometers and other optical measuring devices.

My Leica 8x32BA has been tested with all of the above and some others as well. It was my practice instrument and my reference bin. So far the star tests have been consistent with all the different boosters used. I have not tested with the Barska but will do that in the near future. My 8x20 Ultravid has been tested with multiple boosters also.

EDIT: I just noticed Henry’s post and I think the middle paragraph covers all the bases for me.

Best to all.

Ron

elkcub said:

Hypothetical questions: If telescope A had known aberrations and telescope B were perfect, would it make a difference which one was used as the booster for the other? If they both were imperfect, but in different ways, would the order reveal a difference?

Cheers,
Ed

Click to expand...

In order to give you the unquestionable proof you are looking for, I have verified this question with a ray-tracing software.
The binocular A is a 10x50 model, the additional device B is a 8x20 model. You can see the entire system A+B in the figure.
I have chosen in each case aberrations in the objective lenses that produce a strehl ratio of 0.426 (the strehl ratio of a perfect system is 1).
When the aberrations are applied to the binocular A, the resulting strehl ratio of the entire system A+B is 0.426, because B is optically perfect.
When the aberrations are applied to the binocular B, and A is perfect, the strehl ratios for the entire system A+B are :

Astigmatism : 0.997
Coma : 0.999
Spherical aberration : 1.000

So, there is no doubt that aberrations in the additional device B have absolutely no influence on the resulting image.
The reason can be seen on the figure : the objective of the binocular B is used over a 5 mm pupil, which represents only 6.25% of its total surface. So, even if the objective is affected by large amounts of astigmatism, coma or spherical aberration, a so small part of it can be considered as a perfect lens.

Jean-Charles

jcbouget said:

In order to give you the unquestionable proof you are looking for, I have verified this question with a ray-tracing software.
The binocular A is a 10x50 model, the additional device B is a 8x20 model. You can see the entire system A+B in the figure.Jean-Charles

Click to expand...

Thanks Jean-Charles,

That approach never even occurred to me. Your results are very reassuring.

Best
Ron

Thanks, Jean-Charles, for doing the theoretical part needed to keep faith in the booster method.

I would like to add one bit of practical caution, mainly for those who have not used boosters much yet but are going to try - Henry and Ron surely have come across this already. That is, if the small part of the objective of the booster that takes in the light from the optics that is being tested includes the prism roof edge of the booster, the roof edge can cause enough problems to the image of the booster to visibly compromise the evaluation of the star-test. In this special case, the aberrations of the very small area of the booster are actually significantly higher than the compound aberrations of the whole objective. This is more a problem when viewing a tightly focused star-image, and can be overcome by placing the image just slightly off-axis in the booster image. This, of course, is not a problem if one uses a porroprism binocular or a standard, high-quality finderscope as the booster, but it can be a factor when using boosters such as the Zeiss 3x12 or the Leica 8x20 Ultravid, both of which I use. Although both of these have a very well-ground roof prism, its effect can be seen (and ignored, to a large extent, when you know what it is) when the roof edge line crosses the diffraction image being examined.

Kimmo

P.s. Ron, I think that you have had such a steep learning curve recently that I'm beginning to feel a bit uneasy whenever you cite my experience as surpassing yours.

All,

Thanks to everyone for an interesting and enlightening discussion, as well as the labors that went into it. From my bookish and theory oriented perspective, the sine qua non is the ray tracing analysis provided by Jean-Charles, although everyone else's explanation is certainly consistent with it. My skepticism has been overcome.

Jean-Charles, what ray tracing software to you have? Most things of interest to me could be answered with it.

Ed

John-Charles, that is good work. Thanks for the ray tracing and calculating, and also for the interpretation, without which computer model calculations don't teach anything but only gives "answers".

I was also interested in your opinion on the supposed topic, that the roof prism phase shift effect is usually buried in larger aberrations. I don't guess there ever were two roof binos, identical except one was phase corrected and one not. Phase corrections are usually implemented along with other improvements, so it's impossible for a normal user to tell what change did what.

But, I've see a photograph of a diffraction patterns from roof prisms that were not phase corrected, where the pattern was double. Just curious, have you or Ron or Henry ever seen anything like that in your boosted tests, and does phase correction really eliminate the problem?
Ron

ronh said:

I don't guess there ever were two roof binos, identical except one was phase corrected and one not. Phase corrections are usually implemented along with other improvements, so it's impossible for a normal user to tell what change did what.

Click to expand...

Au contraire (and I've posted on this before ... earlier in the thread ... )

http://birdforum.net/showpost.php?p=1302914&postcount=17

But it's also on another thread with links to the original.

Zeiss 10x40B Dialyt had the same optical design but changed coatings over its lifetime.

You can even do a three way comparison giving two sets of results: single layer versus multilayer (T*) AR and PC (P*) and no PC (both with T*)

T* makes a small difference.

P* makes a big difference.

The main issue with lack of PC is a loss of resolution perpendicular to the roof (from the diffraction pattern I've seen resolution drops between 2x to 3x).

EDIT: here's the text from

http://home.europa.com/~telscope/listpr50.txt

Subject: On the effects of phase-corrected prisms in roof prism binoculars
From: HOldenburg@___m
I'm sure everyone here knows that roof prism binoculars *without phase-corrected
prisms* are optically quite clearly inferior to those with phase-corrected prisms.
The reasons underlying this problem have long been known. Albert Koenig and Horst
Koehler, for instance, mentioned this effect in their book "Die Fernrohre und
Entfernungsmesser" (3rd edition, 1959). An excellent explanation was published by
Adolf Weyrauch and Bernd Doerband in 1988 in the "Deutsche Optikerzeitung".

I got my first pair of roof prism binoculars with phase-coated prisms, a pair of
Zeiss 8x30B's, immediately after Zeiss started selling them, and I found the
difference in direct comparisons to older Zeiss 8x30's quite marked. It was
basically just as Weyrauch/Doerband had written in their paper - better resolution,
slightly higher contrast, overall a "more pleasing image".

Last autumn I finally had a chance to do a more detailed comparison. We (a couple
of fellow birders and I) got together for a weekend trip, and as there wasn't much
about we had the time to do a detailed comparison of three different Zeiss
10x40B's. The first one was bought in 1979. It doesn't have T* coatings and the
prisms are not phase-corrected. The second one was bought in 1981, with T* coatings
but still without phase-corrected prisms,. The third one was purchased in 1998, so
it has both T* coatings and phase-corrected prisms.

The interesting thing about this comparison was that all three binoculars were of
the same make and had the same specifications, so all the differences observed were
caused by the different coating technologies used. We compared the binoculars
mounted on tripods, checking for their optical quality by looking at birds and a
Zeiss standard resolution target in a variety of light conditions.

Perhaps the most interesting result initially was that the differences between the
two old Zeiss 10x40B's weren't all that great. Sure, the T*-coated pair had
slightly better contrast with cleaner colours and a slightly brighter image, but
the difference was nothing to boast about. Even under difficult lighting conditions
the difference wasn't that great. The resolution was exactly the same (as it should
be), and the image of both was slightly fuzzy. This was most noticeable when
checking the resolution targets.

The comparison with the pair with phase-corrected prisms was almost a foregone
conclusion after these results. And sure, it had much better contrast and cleaner
colours, a brighter image and quite clearly a higher resolution than either of the
two pairs without phase-corrected prisms. In fact, the difference was nothing short
of amazing.

I believe this comparison puts some of the claims made about modern multicoatings
into perspective. Modern multicoantings are nice, but they're not the most
important thing to watch out for in roof prism binoculars. Based on this
comparison I'd say the most important progress has not been the development of
modern muticoatings, but rather the development of phase-correction coatings on the
prisms.

One other interesting observation we made was this: After we'd done our comparisons
I got my old Zeiss West 10x50 Porros (~ 1963) from the car. My friends had got
bored with testing optics by that time, so we only did a quick comparison with the
new Zeiss 10x40B's, and the results were pretty amazing. Sure, the 10x40's had
better contrast and a brighter image, after all, the old 10x50's only have a simple
single-layer coating, but the resolution of the old 10x50's was quite noticeably
*better*. In fact, the difference was so pronounced that we couldn't help but
wonder why Zeiss doesn't make these binoculars with a modern T*-coating anymore.
I'm sure they'd beat most (if not all) roof prisms hand down.
Hermann Oldenburg

Click to expand...

The site index (with lots of random interesting stuff!) is at

http://home.europa.com/~telscope/binotele.htm

Wow! This was the most fantastic thread ever! I normally wouldn't look at the topics in the lower half of the forum so I didn't notice this tread till yesterday. The article on phase coating in the tiltle of the thread caught my attention and then I find are discussing what I awalys wanted to say myself!! I am fully aware of the inherent superiority of the porro prism design and I agree that it has been mostly cirumstances and marketting trends that has led to the $2000 a peice roof binoculars which can only approximate the quality of a comparable porro design.

One day I'll form my own optics company to make the best porro-prism binoculars possible with current technology!! but while we are waiting for that day to come I invite you to enjoy this beautiful piece of music as a reward for your great contributions to this thread. It's from the 1981 French movie Le Professionnel :t:

Omid,
Oh well, Porros only approximate the elegance of the roofs. The compact convenience and exacting feel of my Trinovid BA competes with the view through my Fujinon. Someday maybe we can have it all in one binocular. In the meantime, we're not exactly suffering like the early Christians! (Who, I believe, had no binoculars at all.)

Thanks for the music, which I found refreshing after a hard day.
Ron

Kevin said "Au contraire (and I've posted on this before ... earlier in the thread ... )"

Kevin,
I guess I blinked, and missed that the first time! Thanks for pointing out the comparison of the three coating-different-only binoculars. This makes it sound like P coating helps a lot, but does not quite get it up to Porro level.

The Peter Abrahams pages are mind boggling.
Ron

ronh said:

I was also interested in your opinion on the supposed topic, that the roof prism phase shift effect is usually buried in larger aberrations. I don't guess there ever were two roof binos, identical except one was phase corrected and one not. Phase corrections are usually implemented along with other improvements, so it's impossible for a normal user to tell what change did what.

But, I've see a photograph of a diffraction patterns from roof prisms that were not phase corrected, where the pattern was double. Just curious, have you or Ron or Henry ever seen anything like that in your boosted tests, and does phase correction really eliminate the problem?
Ron

Click to expand...

A long time ago I looked through a Zeiss 8x56 BGAT without P coatings. I remember that for astronomy, the Zeiss was somewhat odd, because each star was at the centre of a faint cross. I have scanned an old Zeiss brochure that shows this phenomenon in a very realistic way. You should look at your screen one meter away, and imagine this is a chain of close double stars.
This effect was invisible in the daylight, but I suppose that it reduces slightly the contrast of the image.

I have now a very cheap 10x25 binocular without phase coating. The image is rather soft, but the star test shows other optical aberrations that may bury the phase shift effect. In the star test the Airy disc is clearly elongated in the focused image, like in this page :
http://www.zbirding.info/Truth/prisms/prisms.htm
In my two other roof prism binoculars, the Zeiss 10x40 BGAT*P and Zeiss 10x42 FL, there is no trace of the little cross even on the brightest stars, and the Airy disc appears to be as round as possible considering the presence of other aberrations. So I think that well made phase coatings are very effective.

Jean-Charles

Thanks again Jean-Charles. That is the photo of the diffraction pattern that I saw. I thought the cross was caused by a roof edge that was not cut perfectly sharp. I don't understand, but if Zeiss says it, I guess I'd better believe it.
Ron

Kevin, Ron and others,

What optics journals (e.g. Applied Optics, J. Opt. Soc. America, etc.) publishes articles on the state of the art in the binocular/terrestrial telescope industry?

Omid said:

Kevin, Ron and others,

What optics journals (e.g. Applied Optics, J. Opt. Soc. America, etc.) publishes articles on the state of the art in the binocular/terrestrial telescope industry?

Click to expand...

I would doubt anyone them publish much (I haven't seen much but I don't get a big chance to look). Most of the technology in binoculars/spotters is "well understood" from the optical science point of view. A real innovation may appear there but they are few an far between (phase compensation in 1966 was the last one, I think).

Perhaps a good bet would be to find review papers (that summarize the published literature not tell you how well a product works) that give you an overall view of the field.

But today a optics textboook is perhaps the most likely to give you the details you want (and some of the "known" technical background).

Most of the work in both of these fields are in design (enclosure, baffling, mechanical design) or engineering (product or production) or in tweaking known processes (developing new variants on phase coatings or AR coatings).

Another good area to look is patents ... Google Patents makes it easy (easier ) to find patents for current and recent products. If a company does something novel in design, engineering or production you are more likely to see it in a patent than in a journal. For example you can find the Bushnell Rainguard patents (but remeber that binoculars are "binocular telescopes" or "telescopes" and marketing/brands are not mentioned).

And always remember some some issues are "trade secrets": they're not published and it's made clear to the employees that the process or method or composition is a trade secret and not to be disclosed. I suspect this is less used to day as reverse engineering (even things like layer composition in AR or phase coatings) is "easy". Those reverse engineer-able things should be protected with patents were possible.

Omid said:

Kevin, Ron and others,

What optics journals (e.g. Applied Optics, J. Opt. Soc. America, etc.) publishes articles on the state of the art in the binocular/terrestrial telescope industry?

Click to expand...

Omid, I do not subscribe to anything. All the information I get on latest technology is right here on BF. I did forward your request on to a member of the HST team, thought he may have more information. From what I have seen, optics folks are worse than magicians about secrets. Below is his reply.

Ron, I'm probably the wrong person to ask. Theres a bunch of
journals put out by SPIE (Optical Engineering, etc.) with stuff.
But I'm not sure how much you will find directly related to binoculars
and telescope industry. A lot of what you 'd like to know about will
be trade secrets and proprietary. Also these journals can be very
expensive, since there is no advertising to defray costs
(several $100s per year).

Have a good day.
Ron

OK, so there is no particular journal covering "our field" As you guys mentioned it makes sense beacuse the field is well-established and there is little room for R&D other than new production methods (e.g., using Chinese instead of German labor) or finding better (e.g., cheaper) plastic materal. In that sense it is like firearms manufacturing. I have a Weatherby catalog from 1972 and one from 2008 and you can see that all the exciting new guns in the new catalog are just lower quality versions of those nice ones in the 70's catalog..

Time for me to make a breaktrhrough in this stalled field!!

A (manufacturing) breakthrough: that already happened with the Chinese EDs this year.

Using inexpensive but high quality ED glass objectives, LaK lenses in the eyepeices, latest optical design software, improved and new coatings (including hydrophobic and lipophobic coatings), with improved manufacturing techniques (for accurate assembly) and (potentially) aspherical lenses.

Chinese labour doesn't have a lot to do with robot assembly of most bins today. The humans are doing the other design, marketing and manufacturing tasks (i.e. moving stuff around and checking things).

Combined with better processes this is pushing the costs down. The Chinese have the incentive to do this. The Euro makers ... no so much

The Europeans have already gone down this route of figuring out how to make excellent bins in the 1990s and now perhaps put more effort into making more ergonomic bins as they can already do the rest of a regular basis (and for a price).

There are no "breakthoughs" left to be made: making optics is understood. But making better optics inexpesice more reliable and more easy to use are where the remaining challenges lie. That's a challenge for the Chinese in the next decade or so -- the current Chinese ED bins are functional but not amazing in this department.

OK, perhaps one "breakthrough" (though it's already been done) is inexpensive IS bins. After they get top end bins sorted we might start to see this but a lot of the technology is still protected by patent so we may have to wait until those patents expire.

Kevin,

The one really significant breakthrough that still remains, unfortunately, to be made is image-stabilized binoculars that would be: 1) free of image-degrading stabilization artefacts, while 2) offering premium all-round image quality in 3) an ergonomically pleasing instrument that weighs well under a kilogram. Canon's current top model comes rather close on 1), meets it or fails depending on QC/assembly tolerances of the specific unit being examined on 2), and leaves much to be desired (to put it kindly) on 3). I have no doubt it can be done, and will be done hopefully within the next 10 years.

In the mean time, I'm putting up with an unpleasantly bulky and heavy brick of a binocular, with uncomfortable eyecups and slow focus, because I simply cannot enjoy a binocular image compromised by the shake of my rather healthy and steady hands anymore after stupidly allowing myself to become accustomed to IS.

Kimmo

Kevin Purcell said:

A (manufacturing) breakthrough: that already happened ......

Click to expand...

The daily Shanghai Gospel Show ....
Yaaaaaaaaaaawn!

It's time for you to come up with some solid performance data of your "wonder instruments"! Measurements by an independent source, according to acknowledged ISO protocols, on a comparative basis.
Include one or two units of the usual suspects (the european troika) as a reference.

Happy to receive a table with MEANINGFUL data after months of reiterating rattling of the prayer mill,

T

Kimmo, Finns stick? You could invent a stick suitable for both sauvakävely and temporary tripod.