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patter1
professor emeritus
Reged: 01/19/05
Posts: 594
Loc: Canada
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I came across this review:
http://www.chuckhawks.com/leica_8x25_binoculars.htm
And about 1/3 down there's this part:
"I tried really hard to find the bane of roof prism binoculars, chromatic aberration. It was noticeably absent from this glass, due to the inclusion of an achromatic lens in the objective group (also referred to as Apo or Aspherical), which has long been used as a color focus correcting technology in high end telephoto camera lenses."
Isn't this implying that chromatic aberration is inherently more of a problem in roof prism binocs than porro prism binocs? Assuming the same objectives and eyepieces, I can't see why this would be the case (the need for phase correction is unrelated to chromatic aberration as far as I know).
I'll overlook the thing about aspherical = apochromatic. 
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Patrick
8" f/6 NewStar dobsonian
Orion Starblast 4.5" f/4 mini dobsonian
42mm SuperView, 17mm Nagler T4, some other cheapies
Omcon 7x50, Oberwerk 11x56, Olympus DPS-R 7x35, Olympus Magellan 8x25
homemade 50mm right-angle bino-scope prototype
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MIKADO
member
Reged: 03/21/06
Posts: 52
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I think that there are confusion between chromatic aberration and sphericity aberration.
Simply, here are what one can say on apochromatism and the aspheric lenses.
The refraction of the light depends on the wavelength. In fact each color has a certain wavelength. The chromatic aberration corresponds to a certain maculation of the colors, because the various wavelengths which are focused in points different isolated from the point of focusing. More one objective has a great focal distance, more its chromatic aberration is marked.
To correct this chromatic aberration, an achromatic element is often used.
However, ordinary optical glasses, can be only corrected for two primary education colors of the spectrum of the light. Only the fluorite which is a crystal, has a rate of abnormally low refraction and a weak dispersion that ordinary glass cannot reach. It has also an abnormal dispersion wavelengths of the green to blue. By incorporating fluorite in the objectives, the hearths of development of the three primary education colors red, green and blue, meet in only one point for an ideal correction of the chromatic aberration. As for glass ED, it is special optical glass with the properties close to those of the fluorite. The effect of two elements out of glass ED is almost equivalent to that of an element in fluorite.
The traditional spherical lenses have an inherent defect in their design : the hearth of development for the center of the lens does not correspond to that of the periphery.
The spherical aberrations of the objectives with large opening cannot be corrected only starting from spherical elements. This is why the aspheric lenses were developed. The curve of an aspheric lens is calculated and worked to reach a hearth of development ideal single. It results from it a contrast raised with a minimum from parasitic reflections, even with an objective with large opening.
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patter1
professor emeritus
Reged: 01/19/05
Posts: 594
Loc: Canada
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Thanks. I understand chromatic and spherical aberration, I'm just looking for an explanation as to why the reviewer seems to be saying that chromatic aberration is a problem in roof prism binocs (which might be interpreted to mean that it's worse than in porro prism binocs). Unless he just means that chromatic aberration is a problem in binoculars in general.
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Patrick
8" f/6 NewStar dobsonian
Orion Starblast 4.5" f/4 mini dobsonian
42mm SuperView, 17mm Nagler T4, some other cheapies
Omcon 7x50, Oberwerk 11x56, Olympus DPS-R 7x35, Olympus Magellan 8x25
homemade 50mm right-angle bino-scope prototype
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KennyJ
Reged: 04/27/03
Posts: 10081
Loc: Lancashire UK
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I suspect that Mikado's reply above contains some very interesting points which , sadly , to some extent , are suffering from minor flaws in translation .
I also think that Patrick is correct to interpret the original reviewer's assertion as being that IN HIS OPINION , roof prism binoculars are " more prone to suffer from chromatic aberration " than porro prism binoculars .
I also happen to agree , for what it's worth , with Patrick's understanding that phase correction ( special coating of ROOF PRISMS ) per se , does nothing to correct chromatic aberration , which I always understood , in theory , to be related to the limitations of achromatic OBJECTIVE lenses .
There ARE several CN members , sadly most of whom have not posted here for a considerable time , who could provide some VERY insightful contributions to this particular thread .
Regards , Kenny
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Two eyes and a preference to use both
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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pcad
Pooh-Bah
Reged: 01/17/05
Posts: 1487
Loc: Connecticut
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Patrick,
I have to agree with you, Kenny and Mikado. The statement doesn't make sense. The traditional bane of roof prism binoculars is that there's destructive interference which decreases brightness and perhaps contrast. I'm not sure about the contrast part. Aberrations can be caused by the roof edge also.
I think there are two reasons why he did not see the bane of all roof prism binoculars in reviewing these binos. The first is that they're phase correction coatings on the prisms. Second is that they're made by Leica. I would hope that the prisms would be made well enough that the roof edge wouldn't have any obvious defects and the p-coatings were correctly done.
I think it was just an honest mistake on his part. The result is still that the binos he tested worked well, regardless of the roof prism bane.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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BillC
on a new path
Reged: 06/04/04
Posts: 2099
Loc: Washington, USA
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And while we're in the correcting mode--members, not aberrations--APO and Aspherical do not mean the same thing.
Cheers,
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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patter1
professor emeritus
Reged: 01/19/05
Posts: 594
Loc: Canada
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Thanks Mikado, Kenny, Peter & Bill. Related question:
If you had two identical, optically good, roof prism binocs, the only difference is that one has phase correction coatings, the other doesn't, would the difference in brightness be:
-easily noticeable?
-noticeable but modest?
-difficult to see a difference?
Thanks.
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pcad
Pooh-Bah
Reged: 01/17/05
Posts: 1487
Loc: Connecticut
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Patrick,
Caution! The following is only my opinion!
I believe that phase coatings only allow a roof prism to work as well as it could work. If a roof prism could be made accurately enough initially, it might not even need phase correction coatings. I think that using phase coatings allows a manufacturer to fine tune a prism so they don't have to make each prism to an absurdly high tolerance.
So, a perfect roof prism should work as well as a phase corrected roof prism. Whether you see a difference will depend on the two prisms you're comparing.
From a manufacturing viewpoint, if you have a process that will make excellent prisms from average prisms. It's probably cost effective to optimize the process and save a ton of money by using less expensive glass. Sure it's expensive to set up a coating and testing facility, but once it's done you can make all the perfect prisms you want.
Bill and others, If you think I've been eating too many mushrooms, feel free to correct me. I've never worked in the optics industry like some of you guys have.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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BillC
on a new path
Reged: 06/04/04
Posts: 2099
Loc: Washington, USA
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Phase coatings are about resolution, not contrast, except as it relates to resolution.
Look through the bino in question and then place your half of the last segment of your little finger over one objective. That's a huge portion of your surface area blocked. BUT, did you notice a difference in brightness?
Bingo.
Cheers,
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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pcad
Pooh-Bah
Reged: 01/17/05
Posts: 1487
Loc: Connecticut
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Bill,
Resolution it is then. So a poor roof prism experiences a loss of resolution.
Would this be similar to the decreased resolution associated with reducing the aperture?
I wasn't sure about the contrast part anyway.
Thanks!
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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BillC
on a new path
Reged: 06/04/04
Posts: 2099
Loc: Washington, USA
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Pcad:
Just because a person is a known blowhard, it does not follow that he really knows what he is blowing hard about.
I have never designed a system around phase coatings. However, I did publish a fine article by a couple of Zeiss engineers on phase coating in issue 8 or 9 of ATM Journal. I believe the coating in roof prism instruments are needed because the light path in one half of the cone is a slightly different length that the other. Thus, the coating is to aid in keeping one wave from canceling another and has nothing to do with the quality of the roof edge itself.
Of course, I could be wrong. I was once. But, that was in 58 and I was only 7! 
[I just thought I would throw that in for those who already think I’m too much of a hotdog.]
Cheers,
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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mooreorless
Carpal Tunnel
Reged: 07/05/05
Posts: 1535
Loc: Cornpropst Mills,Huntingdon,Pa
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Quote:
Pcad:
Just because a person is a known blowhard, it does not follow that he really knows what he is blowing hard about.
I have never designed a system around phase coatings. However, I did publish a fine article by a couple of Zeiss engineers on phase coating in issue 8 or 9 of ATM Journal. I believe the coating in roof prism instruments are needed because the light path in one half of the cone is a slightly different length that the other. Thus, the coating is to aid in keeping one wave from canceling another and has nothing to do with the quality of the roof edge itself.
Of course, I could be wrong. I was once. But, that was in 58 and I was only 7!
[I just thought I would throw that in for those who already think I’m too much of a hotdog.]
Cheers,
Bill
Hi Bill,I'm no optics expert or anything but I think you just hit the nail on the head here about phase coating.Having not had time to read the article until now.I will delete the rest of my post.
Regards,Steve
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Regards,Steve M
"the eights are better" Jim Carmichel of Outdoor Life magazine
Edited by mooreorless (07/31/06 05:31 PM)
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grbrown
professor emeritus
Reged: 07/09/05
Posts: 643
Loc: Ampthill, UK, 52:02N 0:30W
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I would like to suggest that a bane of forums like this is taking the view of someone who may have only limited knowledge of a specialist topic, then building a discussion around what are essentially shaky foundations, especially when the author is unlikely to respond! I don't see anything in the article in the Chuckhawks item that leaves me in awe of it! 
Elsewhere on Chuckhawks Harleys get extensive coverage, which cannot be bad! 
But back to the underlying issue here. Do roof prism Binoculars have a history of problems with chromatic aberration? Or is the author on a flight of fantasy? I have owned Zeiss and Leica roofs for over 35 years now and don't recall noticing anything unduly detrimental! 
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Graham
"one eye good, two eyes better...the more I look, the more I see"
BT100-45 degrees, plus 35,24,17,13,9mm Sieberts
15x80, 7x50 Steiners
12x50, 10x42, 8x20 Leica Trinovids
7x35 Minolta
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Alan French
Night Owl
Reged: 01/28/05
Posts: 1461
Loc: Upstate NY
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Quote:
[SNIP]
"I tried really hard to find the bane of roof prism binoculars, chromatic aberration. It was noticeably absent from this glass, due to the inclusion of an achromatic lens in the objective group (also referred to as Apo or Aspherical), which has long been used as a color focus correcting technology in high end telephoto camera lenses."
Isn't this implying that chromatic aberration is inherently more of a problem in roof prism binocs than porro prism binocs? Assuming the same objectives and eyepieces, I can't see why this would be the case (the need for phase correction is unrelated to chromatic aberration as far as I know).
I'll overlook the thing about aspherical = apochromatic.
The statement in itself quite nicely shows the writer does not know what he is talking about, so I'd just ignore the review.
Clear skies, Alan
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Alan French
Night Owl
Reged: 01/28/05
Posts: 1461
Loc: Upstate NY
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Quote:
[SNIP]
But back to the underlying issue here. Do roof prism Binoculars have a history of problems with chromatic aberration? Or is the author on a flight of fantasy? I have owned Zeiss and Leica roofs for over 35 years now and don't recall noticing anything unduly detrimental!
The type of chromatic aberration binocular users complain about is lateral color, which is often noticed as color fringes along high contrast "edges" off-axis. While the rest of the system can introduce some lateral color, my understanding is that lateral color is mostly caused by the eyepiece.
Clear skies, Alan
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BillC
on a new path
Reged: 06/04/04
Posts: 2099
Loc: Washington, USA
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>>>The statement in itself quite nicely shows the writer does not know what he is talking about, so I'd just ignore the review.<<<
There seems to be an unwritten law in the universe that says if you're a 1) Master Birder 2) Great Hunter 3) Seasoned Navigator or, 4) Optics Shop Sales Clerk, you MUST be an expert on optics. And, to those who have had the good sense to stay away from optics as a profession, these folks can keep the mystique. But, then . . .
Once, when I was bemoaning the fact that I have a hard time getting ink in any of the birding magazines, one of America’s senior master birders (who, through his financial affiliations must remain nameless) told me: “Many editors just don’t know what it is they don’t know.” He continued by saying that when they (editors) need a quote, they just pick up the phone and call an “expert” whom they have known for a few years and who may not know as much about optics as they do, but who have a high profile in their specialty.
And so it goes.
Cheers,
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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grbrown
professor emeritus
Reged: 07/09/05
Posts: 643
Loc: Ampthill, UK, 52:02N 0:30W
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Quote:
>>>The statement in itself quite nicely shows the writer does not know what he is talking about, so I'd just ignore the review.<<<
There seems to be an unwritten law in the universe that says if you're a 1) Master Birder 2) Great Hunter 3) Seasoned Navigator or, 4) Optics Shop Sales Clerk, you MUST be an expert on optics. And, to those who have had the good sense to stay away from optics as a profession, these folks can keep the mystique.
Bill,
Even some us mere amateurs can tell an optics dimwit from a 1000 paces! When a new birding magazine started here in the UK their reviews of scopes and bins were dire and seriously misleading (may still be - I don't read it any more). I wrote offering a few suggestions but my letter neither got answered nor published. 
Indeed I have come across several websites recently that cover hobbies which rely on binoculars, but are guilty of publishing misleading information, especially on choosing and buying new ones. 
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Graham
"one eye good, two eyes better...the more I look, the more I see"
BT100-45 degrees, plus 35,24,17,13,9mm Sieberts
15x80, 7x50 Steiners
12x50, 10x42, 8x20 Leica Trinovids
7x35 Minolta
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