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Historical Review of Swift 804 Audubon Binoculars (2 Viewers)

elkcub said:
Henry,

I missed your post at the end of the last page. As I recall you own a Zeiss FL. True? Does "FL" refer to a fluorite crystal lens being present (I know it's discussed on other threads, but forgot), and if so do you get similar perceptual effects concerning the fidelity of color gradation? Being an artist I know you would appreciate that quality.

Ed

Ed,

Yes, I have an 8x42 FL. No, it doesn't use Fluorite. It uses one of the fluoro-crown glass types. Zeiss says something like "glass containing Fluoride ions". I can see from tests with the magnification boosted to 64x that longitudinal CA in the FL is about 1/4 the level I see in typical binocular achromats.

I saw your post about color gradation. I don't think I can report anything similar with the FL, but I'm a chronic malcontent when it comes to binocular optics. They're never as bright or sharp or vivid as I want them to be. I think the FL stands up well compared to other binoculars. The center of it's field has a "transparency" compared to others which makes almost everthing I've compared it to look slightly veiled and dull. But if I compare one barrel of the FL to my Takahashi Sky-90 Fluorite doublet, stopped down to 40mm with an 8x eyepiece to make it optically an 8x40, then the FL image looks shockingly soft, dim and low contrast. A ridiculous comparison, I know, except that it demonstrates how much room for improvement there still is in binocular optics.

Henry
 
henry link said:
Ed,

Yes, I have an 8x42 FL. No, it doesn't use Fluorite. It uses one of the fluoro-crown glass types. Zeiss says something like "glass containing Fluoride ions". I can see from tests with the magnification boosted to 64x that longitudinal CA in the FL is about 1/4 the level I see in typical binocular achromats.

I saw your post about color gradation. I don't think I can report anything similar with the FL, but I'm a chronic malcontent when it comes to binocular optics. They're never as bright or sharp or vivid as I want them to be. I think the FL stands up well compared to other binoculars. The center of it's field has a "transparency" compared to others which makes almost everthing I've compared it to look slightly veiled and dull. But if I compare one barrel of the FL to my Takahashi Sky-90 Fluorite doublet, stopped down to 40mm with an 8x eyepiece to make it optically an 8x40, then the FL image looks shockingly soft, dim and low contrast. A ridiculous comparison, I know, except that it demonstrates how much room for improvement there still is in binocular optics.

Henry

Henry,

That "rediculous comparison" makes a great deal of sense. But, as you said, once you've seen better all else seems veiled and dull. In fact, I also get a strong sense of "transparency" with the 804ED that I've not seen in my other binoculars, but I didn't refer to that quality. It's like the glass ain't there.

As a brief change of topic, you may recall my pontification some weeks ago about the eye-ocular interface being the last frontier (which is not quite true now that we've hit on this). Well, I finally found an article that gets at that notion, which you might find of interest. The bibliography at the end isn't very long, so it would seem that not much work has been done in this area. I've ordered the B.H. Walker (2000) book from abebooks.com. What's your impression?

Ed
PS. If you ever set up that Takahashi 8x40 rig again, and it's possible, could you try to evaluate avian color tonality, — if you haven't already?
 

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henry link said:
...
But if I compare one barrel of the FL to my Takahashi Sky-90 Fluorite doublet, stopped down to 40mm with an 8x eyepiece to make it optically an 8x40, then the FL image looks shockingly soft, dim and low contrast. A ridiculous comparison, I know, except that it demonstrates how much room for improvement there still is in binocular optics.
...

Henry,

I'm doing a double-take on this. And maybe this is what you were suggesting.

The 804ED is very similar to your stopped down, very expensive, Takahashi with 8x eyepiece. They both actually use ED glass in their objectives, the Fluorite being much more expensive, of course (and air- or oil-spaced?). (We'll leave aside Zeiss' fluoride ion glass, which may or may not be similar in its effects.)

In daylight the eye effectively stops down the 804ED's 44mm objective, in some ways comparable to the Takahashi. The manufacturer (Hiyoshi Kogaku) may have applied more stringent quality contol with this limited production, top-of-the-line, Audubon, as more hand fitting was probably required to mount the air-space objective elements, as well as the improved 5-element eyepiece.

So, it's plausible (to me) that since they share the same basic optical ingredients, the unique Takahashi rig and the 804ED may also produce similar perceptual effects. In essence, you may have simulated one side of the only low-power ED binocular ever produced.

Ed
 
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Ed,

I'm going to have to play the skeptic in this. I'm sure the 804ED is an excellent binocular, but I'm as confident as I can be without seeing it that it still suffers from some of the inherent optical compromises found in other binoculars. An f/4 doublet objective, even with the best ED glass and the best air spaced design will still have lots of chromatic and spherical aberrations and the BAK 4 prisms will add more. F/4 is just too fast to make anything close to an aberration free doublet, even with hand figuring and aspherizing. Binocular designers depend on low magnification to keep the aberrations below the threshold of visibility or at least unobjectionable.

The Takahashi comparison demonstrated to me that the aberrations in even the best binoculars are really not below the threshold of visibility. I used the FL because in a star test it shows very low aberrations by binocular standards. The reason I called the comparison ridiculous is because the stopped down Takahashi "8x40" is a 7 pound, 2 foot long telescope, with an f/12.5 objective and no erecting prism. There is nothing there that could be used in a real binocular. I set up the test just to see how much visible damage the fast optics and erecting prism of a binocular do to the image quality, even at low magnification, when compared to an aberration free reference standard.

I have a friend who owns a non-ED 804 like yours. I'll see if I can borrow that and compare it to the Zeiss FL. BTW the FL does use "ED" glass. Zeiss just doesn't use that term. I would call the objective design a triplet; a cemented doublet air spaced with a singlet. Zeiss calls it a 4 element objective because they include the focusing element.

Henry

P.S.- I couldn't open the PDF attachment. I think I need to update my Acrobat Reader.
 
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elkcub said:
Henry,

I'm giving thought to this issue, but in the meantime you may be able to download the article directly.
http://www.ejournal.unam.mx/revmexfis/no504/RMF50413.pdf

More later,
Ed

The Zeiss FL, even though it sounds extremely well corrected (for a lowly binocular), is nevertheless a roof-prism design. The 804 (ED or not) is a porro-prism. Would that make some difference in the quality of image that Ed is seeing in his 804ED?

I love roof-prism binoculars for their streamlined handling. I have spent some time looking through some top-shelf roofs that have blown me away -- the Swaro 7x42 SLC and Leica 8x42. But I still have a memory of the view through the Swift 804 (non-ED) I used to own. It's central-field image was the best view I have ever seen through a binocular (both on birds and stars). Unfortunately, I had problems with eye-relief...blah-blah-blah.

So I am curious to see what Henry thinks of the 804. I owned the latest edition of the 804 that Swift made. I wonder which edition Henry has access to.
 
Henry,

Going back over your post, I'm afraid I completely misread your statement about the FL being more "transparent" in the center field than other binoculars, which seem "slightly veiled and dull" by comparison. I guess I would say that about the 804ED as well, and accordingly I really have to reach out for an FL comparison. Based on my misread, I fell into thinking that the 804ED really is as good as it gets. (Nice fantasy for only $365 on eBay. :)

With regard to the Takahashi rig, of course, I was deliberately exaggerating the degree of similarity between it and the 804ED. My underlying thought was simply motivated by your last statement "...except that it demonstrates how much room for improvement there still is in binocular optics." Looking at it from my psychologist's perspective, I was inclined to ask, Okay, so how much room is that? Unfortunately, I have no real sense of the improvement you can see. However, I couldn't help but muse about a question having to do with the ultimate in human perception. Might it not be that at some optical point, hopefully more practicable than twin Takahashi rigs, the observer will have reached the limits of what can be perceived? Otherwise put, do the optics have to be that good to get the ultimate perceptual result?

I'm afraid I don't follow why you'd be looking at the standard 804, but if you do be aware that only the latest model is fully multi-coated. Steve Ingraham never reported on that version as far as I know.

Ed
 
elkcub said:
With regard to the Takahashi rig, of course, I was deliberately exaggerating the degree of similarity between it and the 804ED. My underlying thought was simply motivated by your last statement "...except that it demonstrates how much room for improvement there still is in binocular optics." Looking at it from my psychologist's perspective, I was inclined to ask, Okay, so how much room is that? Unfortunately, I have no real sense of the improvement you can see. However, I couldn't help but muse about a question having to do with the ultimate in human perception. Might it not be that at some optical point, hopefully more practicable than twin Takahashi rigs, the observer will have reached the limits of what can be perceived? Otherwise put, do the optics have to be that good to get the ultimate perceptual result?

I'm afraid I don't follow why you'd be looking at the standard 804, but if you do be aware that only the latest model is fully multi-coated. Steve Ingraham never reported on that version as far as I know.

Ed


Ed, I hope you don't mind me butting in on this subject.

If you look at the history of optical design, there have not been any major developments since early in the 20th century -- at least as far as can be incorporated in a binocular. The last major development was phase coating, which really isn't an improvement -- just a way of compensating for a previously existing problem.

But flourite, ED glass, Apo design...all these developments are quite old. Apparently, they have just taken a long time to trickle down to use in binoculars.

But I don't think we (we as in our scientific and technological culture) have reached some threshold where it is no longer possible to improve on what we can see in binoculars. Binoculars really are a sort of forgotten stepchild of technology anyway. They are only used by amateurs and hobbyists of various ilks. Astronomers know that to dramatically improve their telescopic images, they need to put the telescope in space -- it's an incredibly simple, albeit horrendously expensive idea. There is not such a simple idea for the binocular-using birdwatcher or amateur astronomer.

I'm not really a scientist -- though I work in the field -- and I'm definitely not an engineer. But here are some ideas about how small optical instruments such as binoculars and spotting scopes could be improved.

One technology might involve bio-technology...using microscopic organsisms that respond to light and produce color. They are already being used, but very experimentally. Pehaps "glass" will not be the refracting element of the future. Perhaps optical "lenses" will be made of bio-organisms that live in some sort of matrix that refract light and reproduce color more finely than the best flourite optical element.

Perhaps nano-technology will provide the new optical frontier. Billions of molecule-sized photosensitive elements that react to and refract different tiny slices of the color spectrum. Kind of like how giant-telescope mirrors are made of hundreds of smaller mirrors.

At any rate, don't hold your breath for these technologies to be used in small personal optics. The scientists have bigger fish to fry before ground-breaking technologies will work their way down to you and me.
 
trashbird said:
Binoculars really are a sort of forgotten stepchild of technology anyway. They are only used by amateurs and hobbyists of various ilks. \
I think that you can add foresters, mariners, soldiers, coast guardsmen and other rescue and assistance personnel who have a great need for binoculars. However their needs do differ those of bird watchers. For instance, the U.S. Army current standard issue binocular is noted for its size and robustness rather than for sharpness.

Happy bird watching,
Arthur Pinewood
 
Pinewood said:
I think that you can add foresters, mariners, soldiers, coast guardsmen and other rescue and assistance personnel who have a great need for binoculars. However their needs do differ those of bird watchers. For instance, the U.S. Army current standard issue binocular is noted for its size and robustness rather than for sharpness.

Happy bird watching,
Arthur Pinewood

Yes, I was forgetting about the binocular users you mentioned, and if anything, they deserve better optics than a hobbyist. On the other hand, night-vision technology is something very useful to many of the kinds of binocular users you mentioned above, but is of little use to your average birdwatcher.
 
Factoid #2: Non-Air-Spaced 804ED.

trashbird said:
Ed, I hope you don't mind me butting in on this subject.

If you look at the history of optical design, there have not been any major developments since early in the 20th century -- at least as far as can be incorporated in a binocular. The last major development was phase coating, which really isn't an improvement -- just a way of compensating for a previously existing problem.

But flourite, ED glass, Apo design...all these developments are quite old. Apparently, they have just taken a long time to trickle down to use in binoculars.

But I don't think we (we as in our scientific and technological culture) have reached some threshold where it is no longer possible to improve on what we can see in binoculars. Binoculars really are a sort of forgotten stepchild of technology anyway. They are only used by amateurs and hobbyists of various ilks. Astronomers know that to dramatically improve their telescopic images, they need to put the telescope in space -- it's an incredibly simple, albeit horrendously expensive idea. There is not such a simple idea for the binocular-using birdwatcher or amateur astronomer.

I'm not really a scientist -- though I work in the field -- and I'm definitely not an engineer. But here are some ideas about how small optical instruments such as binoculars and spotting scopes could be improved.

One technology might involve bio-technology...using microscopic organsisms that respond to light and produce color. They are already being used, but very experimentally. Pehaps "glass" will not be the refracting element of the future. Perhaps optical "lenses" will be made of bio-organisms that live in some sort of matrix that refract light and reproduce color more finely than the best flourite optical element.

Perhaps nano-technology will provide the new optical frontier. Billions of molecule-sized photosensitive elements that react to and refract different tiny slices of the color spectrum. Kind of like how giant-telescope mirrors are made of hundreds of smaller mirrors.

At any rate, don't hold your breath for these technologies to be used in small personal optics. The scientists have bigger fish to fry before ground-breaking technologies will work their way down to you and me.

Another futurist emerges from its cocoon. Hi there, nice fella :'D

If you interpreted me as suggesting there is or should be a limit to technology or innovation, — nay, nay. What I was suggesting is that the receiving organism sets a limit on the information throughput that's possible via its bio-sensory and processing apparatus, and this sets a corresponding restraint on the technology that's required to reach that limit. Beyond that it's overkill, guilding the lilly, ... and so forth. So, how far do binocularists have to go to get to that bio limit? As Henry already intimated, the Takahashi rig is an "existence proof." It says, "Here is one device, which may go beyond what's needed, but can improve the visual experience significantly." I also see a major step-function improvement in my air-spaced 804ED, so for now it's my personal existence proof that more lies ahead.

Extra, Extra, read all about it: Returning to the historical subject of this thread, Renze de Vries has just now obtained iron-clad proof that (some) later 804EDs were NOT airspaced. Wim de Boer, who is our expert opticalman in The Netherlands, took apart his own specimen and found — a cemented doublet. Yikes. This flies in the face of all that's holy, and a lot that isn't.

Renze may want to chime in here with his own thoughts, but to me although this development presents a brand new set of questions, it also potentially points to a few answers. The big question for me has been, Given the superb view from the 804ED, why did it fade from the scene without a whimper? The answer may simply be that the non-air-spaced version was not as good as the original.

AS ED
 
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Yeah, sorry for the threadjack, Mr. Air Spaced...Mr. Ed?

It seems like having a cemented doublet kind of defeats the purpose of adding ED glass. Cheaper to manufacture, though, I'm sure.

I am thinking of buying another 804 again at some point -- eye relief be damned. If I only get a 360 ft/1000 yd FOV with my glasses, that will still be the best 360 ft/1000 yd view that my money can buy. And at night, eye relief increases anyway -- so I might be able to get 400 ft/1000 yd for stargazing. I would only be missing out on the fuzziest outer part of the view, anyway.
 
Dr. Ed, actually, but there's a lot smarter one on CN. So, I'll stick with AS ED. Air-Spaced ED goes well with my personality and all. :'D

I'd suggest you wait around for a FMC HR/5 Type 4b(2) to show up on eBay, as it will. Is it possible for our futurist to buy contact lenses?

BTW, I guess we will have to re-write the article with Type 4c(1) and 4c(2), 1 being AS, and 2 being NAS. Our labors never end.

AS ED
 
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elkcub said:
Dr. Ed, actually, but there's a lot smarter one on CN. So, I'll stick with AS ED. Air-Spaced ED goes well with my personality and all. :'D

I'd suggest you wait around for a FMC HR/5 Type 4b(2) to show up on eBay, as it will. Is it possible for our futurist to buy contact lenses?

BTW, I guess we will have to re-write the article with Type 4c(1) and 4c(2), 1 being AS, and 2 being NAS. Our labors never end.

AS ED

What's up, Doc?

The FMC HR/5 Type 4b(2) was what I owned, and I would settle for nothing less.

I'll bore you with the story of how I bought them. I saw them in an Astromart classified ad and it turned out the owner lived in my city. So I contacted him, went over to his house and had a look at them. He was a very serious amateur astronomer with some high-end scopes, and though he liked the 804s, he was going to buy the 804ED, which he thought would give him a tad more "oomph" or something. This was maybe maybe 10 years ago, so both the 804 and 804ED were still in production. I can't remember what I paid, but it was considerably less than the new price, and the binoculars were in impeccable condition.

I used the 804s for about a month before I gave up on them for the eye-relief issue. One thing that struck me about them was basically what Steve Ingraham said about them. You can discern details of birds from vast distances, even better than with 10x binoculars. The resolution is that good. Steve Ingraham is also a glasses wearer and the 804s were his personal binocular for many years despite the shallow eye relief.

Contacts...hmmm. I haven't tried them in many years. I have heard they have gotten a lot more comfortable to wear. Also, I'm not sure whether they would fully correct my astigmatism. It's worth looking into, though
 
Thoughts on a rainy day in California

With respect to the prior discussion, I'm increasingly curious why Stephen Ingraham's more recent writings (see quote below, or his full article on Color Fringing at http://www.birdforum.net/article.php?a=2 ) has not led to more extensive discussions about the subjective pleasures of color "vividness," and the "differentiation of finer shades," to use his words. Does anyone have a thought about that? In essence, this is really what my wild-eyed reaction to the 804ED is all about, —color perceptions.

At the risk of sounding critical, which is not intended, I think it is a truism that most of us evaluate binoculars by considering physically measurable properties, such as resolution, DOF, FOV, CA, etc., even though the measurement often requires a skilled human observer. No exception to this is what I refer to as "aided visual acuity," since even this is easily confused with optical resolution. Arguably, Ingraham's innovative NEED Score, using a US dollar bill as a target, also helped to solidify an externalization of what is really an important and relevant internal human performance measure. The point is that what we naturally tend to consider are properties of the external device, probably because that’s what we buy, and not the internal human reactions (e.g., performance improvements, perceptions, feelings, etc.) that it produces. I guess that's fair enough. After all, how many grease monkeys wax eloquent about the sculptural feel of a Snap-On wrench, or electricians the joy of a Klein tool? But, they do have these internal perceptions and will pay a lot more to get them.

Not that he needs more, but here we must pay homage to Mr. Ingraham, once again, as the quintessential binoculars writer. Did you ever wonder just what it is about his BVD reviews that set them apart? Well, here’s one of his tricks as I see it. He actually describes his own visual perceptions, which, more often than not, conform with what the population experiences. There’s no getting around it, folks, as we move into the rarified atmosphere of ED, Fluoride and Fluorite lens technology, more and more the distinctions which define a “Better View” will be perceptual and not easily measured. Unfortunately, it’s the “touchy-feely” stuff a poet is needed to describe.

So where does that leave us? Perceptual ratings of transparency, vividness, and color-shading, among others, can be added with thought to the lexicon of binocular reviews. Informed opinions in this domain are no less valid or trustworthy than any other so-called “objective” opinion, and, of course, they are also subject to the maxim that consensus rules the day. Once manufacturers come to realize that such factors are being looked at by a discerning audience, there would no doubt be greater effort to develop and market a “better view.” Not to worry, based on an economy of scale and competition, today’s high prices would moderate.


... The extra vividness increases your pleasure in the image, makes possible the differentiation of finer shades of colors (especially, for some reason, the blues), and, we are discovering, even at the lower powers common in binoculars, increases color perception in low light situations, enhancing the twilight performance of the optics.
... S. Ingraham, 2004
 
Steve Ingraham was such a good reviewer because he came from humble beginnings. He didn't start out with the top-of-the-line Euro-optics. He carried an inexpensive Nikon compact around his neck for a long time. Then he graduated to the Swift Audubon 804s.

He was a school teacher with a pretty big family. He couldn't afford most of the binoculars he reviewed. He was given them to review because he was such a perceptive and eloquent writer. Take away the NEEDS test. His reviews are still the best.

In addition to his knowledge and perception of the optical experience, he is a very active birdwatcher. I honestly think that there are optics nuts on this forum who really don't do that much birdwatching. Or birdwatching is just a test of the optics, rather than the reason for the optics. I'm afraid I am guilty of that sometimes myself.

More than anyone Ingraham understood how difficult it used to be for the average middle-class birdwatcher to get a decent set of binoculars and not have to go into debt to do so. And I imagine that his reviews and observations of the optics market have contributed more than anyone else to the outstanding quality of mid-priced optics these days.

Steve Ingraham was such a good reviewer that Zeiss basically bought him off so that he would stop reviewing optics and start selling them. And I don't mean that as negatively as it sounds. Ingraham has earned his position as a Zeiss representative and I bet he is still as honest and critical of what he sells as he was about what he reviewed.
 
trashbird,

Very nicely put, and I concur completely. I didn't agree with a few of his conclusions over the years, and was puzzled by some, but his knack at describing perceptions was quite unique. I think this was actually aided by him not having a behavioral science background, so he could weave the concepts into lay terms.

Now, at this point, I wouldn't mind if he extolled the virtues of Zeiss products exclusively. There would be no need to deride other companies or to engage in cross-product comparisons. In fact, given that he's so good at it, I really don't understand why Zeiss hasn't encouraged him to do this already. Who cares if he hawks Zeiss products if he believes in them? We all know the deal. My ulterior motive, of course, would be to bootstrap his considerable skills to codify the benefits of Fluorite technology, or, more generically ED technology, for aided color acuity. He could even do so within the framework of Zeiss products.

Of course, it's easier said than done ...

ED
 
I noticed something in Ingraham's otherwise fine article on color fringing:

"Recently a third alternative has become available to optical designers. FL glass, a special optical glass which is enhanced with fluorine ions, has the advantages of both ED and Fluorite, but without the drawbacks of either. The introduction of FL glass allows the design of systems that are light weight, durable, and which offer superior color correction."

We know from the refractive optics article that the FL glass that Ingraham refers to is fluor-crown glass -- not a recent development at all. In fact, I'm not sure what Ingraham means when he refers to older ED glass being made from rare earths. Unless Zeiss has really come up with a truly revolutionary glass-making method, it would seem that their FL glass is basically what others are simply calling ED glass. This is what Henry Link has stated.

I doubt if Ingraham is being deceptive here. I would hope he is merely spouting the ad copy of the Zeiss marketing department.
 
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Here is a cool link to an optical glossary:

http://jeff.medkeff.com/astro/optics/optical_definitions.htm

It mayprove useful in some of the discussions here. (Speaking of, should this stuff be moved off the Swift history thread?)

I like these definitions:

"ED: short for "extra low dispersion," a reference to glass types that do not disperse light into its component colors so easily as regular glasses. ED glasses therefore exhibit less chromatic aberration by themselves than a typical crown or flint. Not magical."

"Fluorite: a type of "ED" crown glass, discovered by Ernst Abbe, which has low refractive index and low dispersion, as well as an abnormal partial dispersion. Chemically CaF2. Historically, natural fluorspar crystals were used, and applications were limited to microscopes. Development of artificial crystals was necessary to produce elements large enough for use in telescope objectives. Fluorite is about 1/4 as hard as typical glass, and it is consequently delicate and very sensitive to temperature changes. It is considered rather difficult to polish. Fluorite will be degraded by long term contact with water, acids, and other atmospheric contaminants, but in telescope objectives the coatings should protect the surface. Like lanthanum, fluorite has had a good deal of attention by marketing hypesters, and like lanthanum, it is not a magical substance, but provides optical designers with important latitude in improving optical systems. Not magical."

Not magical....waaaahhhhhh!!! *tears*
 
trashbird said:
Here is a cool link to an optical glossary:

http://jeff.medkeff.com/astro/optics/optical_definitions.htm

It mayprove useful in some of the discussions here. (Speaking of, should this stuff be moved off the Swift history thread?)

I like these definitions:

"ED: short for "extra low dispersion," a reference to glass types that do not disperse light into its component colors so easily as regular glasses. ED glasses therefore exhibit less chromatic aberration by themselves than a typical crown or flint. Not magical."

"Fluorite: a type of "ED" crown glass, discovered by Ernst Abbe, which has low refractive index and low dispersion, as well as an abnormal partial dispersion. Chemically CaF2. Historically, natural fluorspar crystals were used, and applications were limited to microscopes. Development of artificial crystals was necessary to produce elements large enough for use in telescope objectives. Fluorite is about 1/4 as hard as typical glass, and it is consequently delicate and very sensitive to temperature changes. It is considered rather difficult to polish. Fluorite will be degraded by long term contact with water, acids, and other atmospheric contaminants, but in telescope objectives the coatings should protect the surface. Like lanthanum, fluorite has had a good deal of attention by marketing hypesters, and like lanthanum, it is not a magical substance, but provides optical designers with important latitude in improving optical systems. Not magical."

Not magical....waaaahhhhhh!!! *tears*

Hi trashbird,

Having started this thread, I took the liberty of veering slightly off track with my rainy day musings (which I can do again today). It's the 43rd day, and truly biblical in scope; Noah only had to stick it out for 40, and he had lots of company. However, I think our discussion is relevant to appreciating the whole Audubon series, not only the 804ED.

"Not Magical" is absoluely a scream! In addition to the other definitions you mentioned, about ED and Fluorite glass, the one on Coatings, antireflection, (incl. multi-coating) is quite good, and clearly conforms with "not magical." More and more I suspect that my "Chinaman's Hat" percept is a result of field curvature. It could also include, or even be, spherical aberration. However, it always flattens out at the edges, which I don't quite comprehend. I'm just looking for an explanation of the phenomenon.

My musing today continues about externalizing our love of the non-magical things inside binoculars, while paying scant attention to the the perceptual magic that occurs inside ourselves. If it looks better viewing through one set of peeper enhancers than another, then they are the better ones no matter what. Well, that's what I'm thinking anyway. BVD means better view desired, after all, and that may not equate completely to lack of aberrations or optical flaws.

How's the weather in Arizona?
Ed
 
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