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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Historical Review of Swift 804 Audubon Binoculars (1 Viewer)

Factoid #1: Tethered Objective Covers

I just received two pairs of rubber tethered objective covers from B&H for the Audubon, at 6.95 each. They are very good quality rubber, and work with my 804R and 804ED very nicely, although I assume they were designed to fit the 820 and 820ED. They are too large for the 828 HHS. The manufacturer is Eagle Optics.

Ed
 
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Greetings!

This is a most fascinating discussion, especially considering that I own an much loved, much valued pair of Audubons, which I wouldn't trade for ANYTHING - by the excellent reference article above, mine would be 804R type 4b(2) - fully multi coated designation. I purchased these in the late 1999, and my serial number is 97****, so they can clearly support the proposed 'year theory'.

I also note that, from the article, my particular Audubons share EVERYTHING with the ED except the actual ED glass itself - including the air spaced objectives and coatings, which the 4b(1)'s do not. This would make mine a perfect candidate for testing the article's assertion that the air spaced objectives may be as important optically as the ED glass itself. It would be interesting to compare a 4b(1), a 4b(2), and an ED side by side - one would think my glass would slot in between them, and perhaps even match the EDs performance-wise, if the assertion is correct. BTW my 804s are in perfect condition, due to the "harsh weather conditions" of Northern California, so if anyone is local and interested, I'll be there...!

All I know is that to my eye, my Audubons have not yet been bested by any comparison I've ever done (even by competitors requiring monthly payments!), and I feel very fortunate to be an original owner of this wonderful birding instrument.
 
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dozercsx said:
Greetings!

This is a most fascinating discussion, especially considering that I own an much loved, much valued pair of Audubons, which I wouldn't trade for ANYTHING - by the excellent reference article above, mine would be 804R type 4b(2) - fully multi coated designation. I purchased these in the late 1999, and my serial number is 97****, so they can clearly support the proposed 'year theory'.

I also note that, from the article, my particular Audubons share EVERYTHING with the ED except the actual ED glass itself - including the air spaced objectives and coatings, which the 4b(1)'s do not. This would make mine a perfect candidate for testing the article's assertion that the air spaced objectives may be as important optically as the ED glass itself. It would be interesting to compare a 4b(1), a 4b(2), and an ED side by side - one would think my glass would slot in between them, and perhaps even match the EDs performance-wise, if the assertion is correct. BTW my 804s are in perfect condition, due to the "harsh weather conditions" of Northern California, so if anyone is local and interested, I'll be there...!

All I know is that to my eye, my Audubons have not yet been bested by any comparison I've ever done (even by competitors requiring monthly payments!), and I feel very fortunate to be an original owner of this wonderful birding instrument.

Now here is a coincidence made in Heaven! We both live in Northern California. I'm in Sunnyvale, — and you? Perhaps we can get our optics together for a comparison.

I'm somewhat confused about your Audubon. If yours were made in 1997 they should be Fully Multi-Coated 804 HR/5s. We refer to them as Type 4b(2). However, I'm not aware, to this point, that any non-ED HR/5 was ever made with air-spaced objectives. Rather, it should simply have the latest multi-coating, which sets it apart from the original Type 4b(1) and earlier 804R (Type 4a).

Can you come up with evidence that your non-ED has air-spaced objectives? If so, this alone would be a juicy addition to the story.

Regardless of this issue, I own an 804R and 804ED that can be compared with your late model HR/5. Let's get together and do it one day soon.

ED
 
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Wow Elk, talk about a small world - I live in Sunnyvale! Sounds like a comparison's in short order (if the rain ever stops!) - Charleston slough and the Black Skimmers, here we come...!

My comment about the air-spaced objectives comes directly from the reference article, section 3, page 18, in the description of the 804ED (!) as quoted here:

"Optically, the air-spaced objective elements may be as significant as the use of ED glass, but that is usually overlooked. It was introduced with the standard type 4b(2) and is the forerunner of the current model 820ED."

My glasses are indeed the FMC, green coating, 804R HR/5 type 4b(2) - whew! - so as per above ,they should have air-space objectives. (I don't know what to look for to indicate such, as the objectives are sealed, so I'm merely taking the article at face value). I suppose the authors could verify how they determined that particular statement - all I know is that my 804's are razor sharp and very, very good!

DozerCSX
 
dozercsx said:
Wow Elk, talk about a small world - I live in Sunnyvale! Sounds like a comparison's in short order (if the rain ever stops!) - Charleston slough and the Black Skimmers, here we come...!

My comment about the air-spaced objectives comes directly from the reference article, section 3, page 18, in the description of the 804ED (!) as quoted here:

"Optically, the air-spaced objective elements may be as significant as the use of ED glass, but that is usually overlooked. It was introduced with the standard type 4b(2) and is the forerunner of the current model 820ED."

My glasses are indeed the FMC, green coating, 804R HR/5 type 4b(2) - whew! - so as per above ,they should have air-space objectives. (I don't know what to look for to indicate such, as the objectives are sealed, so I'm merely taking the article at face value). I suppose the authors could verify how they determined that particular statement - all I know is that my 804's are razor sharp and very, very good!

DozerCSX

Yikes, what a coincidence! Yes, I was at Charleston slough just two days ago. The two dozen or so Black Skimmers were wonderful, as usual, and it would be a good location to make some comparisons now that they built the observation deck to work on. Being retired I can meet with you any day. What's your situation?

Maybe we should talk details by private email.

ED
 
You can determine from the outside whether your objectives are air spaced by examining the reflection pattern that returns from the objective surfaces.

It requires some careful examination and it's good to know what you're looking for. I've found it's easiest to place a single small light source like a bare light bulb behind me. Hold the binocular in front of you with the objective end pointing toward you. Use one eye only to examine the pattern of reflections of the light bulb in the objective. A cemented doublet will return 3 reflections of the bulb, 2 from the coated front and back surfaces of the doublet and 1 very dim (sometimes almost invisible) and usually tiny reflection from the cementing between the elements. An air spaced doublet will return 4 reflections, all of them showing the color tint of the coating. Be careful not to confuse objective reflections with prism reflections which you will be able to see from certain angles.
 
henry link said:
You can determine from the outside whether your objectives are air spaced by examining the reflection pattern that returns from the objective surfaces.

It requires some careful examination and it's good to know what you're looking for. I've found it's easiest to place a single small light source like a bare light bulb behind me. Hold the binocular in front of you with the objective end pointing toward you. Use one eye only to examine the pattern of reflections of the light bulb in the objective. A cemented doublet will return 3 reflections of the bulb, 2 from the coated front and back surfaces of the doublet and 1 very dim (sometimes almost invisible) and usually tiny reflection from the cementing between the elements. An air spaced doublet will return 4 reflections, all of them showing the color tint of the coating. Be careful not to confuse objective reflections with prism reflections which you will be able to see from certain angles.

Henry,

I'll have to work at this a bit harder with an improved lighting set up. However, right now I can see considerable difference between the standard vs. ED objectives. The former shows three distinct reflections, and the latter four — but, they are clustered quite differently and of a different size (smaller). The colors of the reflections are also related to the surface coatings as you said. My Kestrel shows three reflections, like the Standard 804, but the colors are different due to full multi-coating.

Many thanks for the tip. I'll probably comment further after a little more work to perfect the technique. This may come in very handy because there is some (yet unsubstantiated) indication that the latter 804EDs had cemented doublets and were not air-spaced.

Thanks,
ED
 
Elk,

I realized after my last comment that

(1) YOU were the author, so I was already speaking to The Source (!), and
(2) In re-re-reading, I see how I could have misread the quote - "with" could refer to the 804ED itself, instead of an air-spaced objective reference to the 804R 4b(2).

In addition, I checked the objectives this morning as per Henry's insightful instructions, and I definitely did not see 4 reflections, so I think you're right - mine does not appear to be an air-spaced objective. Of course, we can doublecheck when we meet for the full comparison.

Man, ya learn somethin' every day around here! Thanks...
 
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Henri,

What's not discussed here yet is the presumed OPTICAL advantage of air spaced objective lenses versus cemented doublets. I for one don't see any advantages. Do you?

Renze
 
Renze de Vries said:
Henri,

What's not discussed here yet is the presumed OPTICAL advantage of air spaced objective lenses versus cemented doublets. I for one don't see any advantages. Do you?

Renze

The air-spaced doublet objective has two more lens-to-air surfaces than a cemented doublet, making for more reflections. Before multicoating, that was more opportunity for light loss through the objective. Also, cemented doublets are cheaper to make and to mount in binoculars. The cemented lens surfaces don't have to be as well figured as in air-spaced doublets, and more care has to be used to get the individual elements of the air-spaced elements properly mounted and aligned. The benefit of the air-spaced doublets is that they offer more freedom for the optical designer to overcome certain abberations.

Here's an interesting source:

http://www.atmsite.org/contrib/Ceragioli/newrefractor/chapters/Chapter 3b.html

The introductory paragraphs for each section on cemeted and air-spaced doublets are pretty readable. After that, my eyes start crossing. But here is the science of it.
 
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trashbird said:
The air-spaced doublet objective has two more lens-to-air surfaces than a cemented doublet, making for more reflections. Before multicoating, that was more opportunity for light loss through the objective. Also, cemented doublets are cheaper to make and to mount in binoculars. The cemented lens surfaces don't have to be as well figured as in air-spaced doublets, and more care has to be used to get the individual elements of the air-spaced elements properly mounted and aligned. The benefit of the air-spaced doublets is that they offer more freedom for the optical designer to overcome certain abberations.

Here's an interesting source:

http://www.atmsite.org/contrib/Ceragioli/newrefractor/chapters/Chapter 3b.html

The introductory paragraphs for each section on cemeted and air-spaced doublets are pretty readable. After that, my eyes start crossing. But here is the science of it.

Wow, what a fantastic article! When the reader is done, a link to Chapter 4 can be found at the end to tell all about Apochromats and ED glass. Thank you, thank you.

ED
PS. Did I say thank you? :D
 
Trashbird,

Thank you. So by using air-spaced doublets it's possible to make optically better binoculars. But that's theory. How about practice? I mean, can we see the difference? And if so, where (in what binoculars on the market today)?

Renze
 
elkcub said:
Wow, what a fantastic article! When the reader is done, a link to Chapter 4 can be found at the end to tell all about Apochromats and ED glass. Thank you, thank you.

ED
PS. Did I say thank you? :D

You're welcome, ED. Thanks really should go to Mr. Ceragioli, who created this fine website.
 
trashbird said:
You're welcome, ED. Thanks really should go to Mr. Ceragioli, who created this fine website.

trashbird,

Ah, yes, but you get the credit for finding it for us — I've been looking for a comprehensive treatise to no avail.

Renze,

I started this Zeiss thread: http://www.birdforum.net/showthread.php?t=55420 with a similar question in mind. But after 103 viewers there have been no comments. I probably framed the question wrong.

I suspect much of the issue is design implementation. Namely, although I see a stunning improvement in clarity and color gradation using the 804ED (as did Steve Ingraham in '93), other binos using ED or Flourite elements may or may not produce similar results. I wish I had a Zeiss dealer in the vicinity, since they seem to be the most likely candidates for low power binoculars.

ED
 
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I'll add my thanks to trashbird for the link to Mr. Ceragioli's work. Chapter 4 is by far the best information I've seen on APO objectives. Notice that all the objective designs under discussion have much higher focal ratios than binocular objectives. The lowest focal ratio even discussed was the f/6 Zeiss APQ and that's an oil spaced Fluorite triplet. Binoculars belong in a completely different class of optics. The f/3.5-f/4.5 objectives in small binoculars, even if they are triplets and/or use ED glass have much higher levels of aberrations. I've never seen any binocular with optics good enough to reasonably be called a high quality telescope. The optics are just too fast. The subjective image quality only looks good, even in the best binoculars, because the magnification is kept extremely low by telescope standards. Even then the problems are visible, just not obtrusive.
 
Renze de Vries said:
Trashbird,

Thank you. So by using air-spaced doublets it's possible to make optically better binoculars. But that's theory. How about practice? I mean, can we see the difference? And if so, where (in what binoculars on the market today)?

Renze

I'm not sure. I have to defer to Henry. I just found the website.

My Orion Short Tube 80 telescope has an F5 focal ratio (400mm focal length divided by 80mm objective diameter). It has an achromatic air-spaced doublet. It still has all kinds of chromatic abberation at high powers, though. According to the article, doublets larger than 70mm can't be cemented anyway.

What I hear ED saying about the improved optical quality of his 804ED's is that there is a greater saturation of color, not that there is necessarily much less chromatic abberation. Perhaps that is the most noticible benefit in using ED glass in a low focal-ratio design. The color saturation is so profound that chromatic abberation "appears" much less noticible. Dunno, just a WAG.
 
trashbird said:
I'm not sure. I have to defer to Henry. I just found the website.

My Orion Short Tube 80 telescope has an F5 focal ratio (400mm focal length divided by 80mm objective diameter). It has an achromatic air-spaced doublet. It still has all kinds of chromatic abberation at high powers, though. According to the article, doublets larger than 70mm can't be cemented anyway.

What I hear ED saying about the improved optical quality of his 804ED's is that there is a greater saturation of color, not that there is necessarily much less chromatic abberation. Perhaps that is the most noticible benefit in using ED glass in a low focal-ratio design. The color saturation is so profound that chromatic abberation "appears" much less noticible. Dunno, just a WAG.

Slight correction. The most notable quality improvement I see is continuous color gradation. Smooth color variations are more evident and less like a solid block when viewed with the 804ED. For me, the effect is stunning. I can't describe the perceptions any better than Steve Ingraham did in 1993 (see below), but I would say that his subjective description holds up well not only against the standard 804, but also all the other binoculars that I own. Unfortunately, I now find the others are missing something, — which is the down side.

I haven't had a chance to read all the technical material in detail, but my impression from yours and other sources is that the historical motivation for ED, Fluorite, etc. has been primarily astronomical applications. The color perception effects with low power optics for daylight terrestrial uses have not been considered much (strangely enough). In this regard, I would think we should be careful in generalizing, because the photo-chemical (photopic) adaptation and capabilities of the eye are very different in daylight. Color perception is minimal under dark adaptation (scotopic) conditions, and subtle daylight optical effects, such as these, would be literally impossible to appreciate at night.

Additional thoughts: There is a slight color fringing even with the 804ED at the extremes of the field, and the current 820ED is also said to be air spaced. Overall, I tend to think that Swift's use of ED glass is more or less joined at the hip with air spacing, i.e., by design, and so the contributions of glass and mechanics are essentially not separable. (Renze, if it turns out that some later 804EDs were not air-spaced, then the original optical design was most likely modified to allow the lenses to be cemented. But, that's not been verified yet, to my understanding.)

ED
The ED glass in the objective does, as you might expect, improve color depth and definition. Colors are slightly more intense, and you can see more different shades and gradiations of the same color. The yellow of a Meadowlark's breast or the blue of a Mountain bluebird's, one solid color through standard binoculars, shows an amazing range of subtly different hues through the ED glass.
 
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Point taken, ED. In birdwatching, color representation in the image is paramount. Both for enjoyment of the view and identification. Most birds are colorful. Even birds that look brown or grey in the distance, show subtle color variations with even cheap binoculars. I never realized how many Western Kingbirds there were in the suburban neighborhoods of my city. From a distance they all looked like mockingbirds or something to my untrained and non-binocular-enhanced eyes. Put a binocular on them and you see their lovely yellow chest and belly. Of course, now, I also know what a kingbird looks like by its flycatching movements.

At any rate, I think you're right about nighttime and daytime human optical perception. Color is important to astronomical observers, especially planetary observation, but astronomers use filters to artificially enhance images anyway. The problem with chromatic aberration for astronomical observers is not just the annoying purple or green fringing -- but chromatic aberration actually degrades resolution as well.

Amateur astronomers have now taken to using "minus-violet" filters in their eyepieces. These filters remove a very sharp portion of violet in the spectrum that is most apparent in color fringing. These filters make planetary and lunar images appear more yellowish, but the color fringing from achromatic objectives -- particularly on fast scopes -- is greatly reduced. Observers report better clarity of image as well as reduction of color fringing.

Can this be done in binoculars? I don't see why not. But for birdwatching, any unnatural coloration would defeat the purpose of a birding optic. For hunting, surveillance, astronomy, and many other uses of binoculars, minus-violet filtering might really make binoculars more effective.

I am considering getting one of these minus-violet filters for my Short-Tube 80 scope (which I use for both astronomy and birding). I am curious about the filter's effects for birdwatching. My guess is that in daylight use, the filter would induce too much artificial color for birdwatching use. In low-light situations however, when color in general is reduced and chromatic aberration is more pronounced, I wonder if the minus-violet filter might prove itself useful for bird observation.
 
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henry link said:
I'll add my thanks to trashbird for the link to Mr. Ceragioli's work. Chapter 4 is by far the best information I've seen on APO objectives. Notice that all the objective designs under discussion have much higher focal ratios than binocular objectives. The lowest focal ratio even discussed was the f/6 Zeiss APQ and that's an oil spaced Fluorite triplet. Binoculars belong in a completely different class of optics. The f/3.5-f/4.5 objectives in small binoculars, even if they are triplets and/or use ED glass have much higher levels of aberrations. I've never seen any binocular with optics good enough to reasonably be called a high quality telescope. The optics are just too fast. The subjective image quality only looks good, even in the best binoculars, because the magnification is kept extremely low by telescope standards. Even then the problems are visible, just not obtrusive.

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
 
trashbird said:
...
My guess is that in daylight use, the filter would induce too much artificial color for birdwatching use. In low-light situations however, when color in general is reduced and chromatic aberration is more pronounced, I wonder if the minus-violet filter might prove itself useful for bird observation.

Ah, yes, the issue of absolute color fidelity crops up. I've got a cheap, stark-white bird bath made of plastic. I find the vertical pedistal is an excellent object to produce color fringing, to the point where I can calibrate the width of the green or purple fringes on either side. Being stark white it might also be a a starting point to appreciate the overall effect of color filters, or their ability to attenuate the fringes.

ED
 
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