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What's the difference in ED, FL, and HD glass?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 17:00
tpcollins View Drop Down
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I've seen optics glass described in 3 different terms:
 
ED - Extra-Low Dispersion Glass
FL- Fluoride Glass
HD - High-Defintion Glass.
 
HD gets all of the marketing hype but what's realy the difference between them from  a clarity of view and low light capability point of view? Thanks.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 17:26
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ED and HD are marketing terms used interchangeably and mean the same thing.  It all depends on what terms the manufacturer(s) decide to use.  "FL" is a term used to describe glass that has fluorite in it's composition.  "FL" glass is "ED" / "HD" glass, but "ED" / "HD" glass may not necessarily be fluorite glass.  Though all are considered "low dispersion" or "extra low dispersion" designs.  FL glass is just one method of producing extra low dispersion optics, but other elements can also be used in the composition of the glass to produce ED/HD lenses.  The same can be achieved with multiple, complex glass elements from ordinary flint and crown glass combinations.  Some factors that make an optic considered "HD" actually may have nothing to do with glass and may be related to other design elements such as internal baffling, coatings, and lens element geometry.

From a practical standpoint, the difference between different optics featuring these marketing terms does not follow any predictable pattern in terms of what you will actually see.  In some cases, you'll see the difference; in other cases, you won't.  What's more important is how the optic was spec'ed out, the overall design quality of the entire optic, and what company made it.  Not everyone's "ED," "HD," "XD," "APO," etc. is created equal, and there are no industry standards for defining what exactly makes any particular optic an "HD" model, nor what performance level the optic must achieve before it can be so labeled.  About the only thing the consumer can go by is the so-called ED / HD, etc optics are usually optically superior to the non ED / HD versions from the same brand, but not always by a significant degree and maybe not even at all.  Then, some manufacturers' ED optics aren't as good as other manufacturers' non-ED optics. 
 
Those are very relative terms.  The only one that is specific is "FL" to denote at least one lens element of fluorite glass, but having FL glass doesn't mean a whole lot if the overall design of the optic isn't optimized to take advantage of the extra low dispersion benefits of the FL glass.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 18:00
tpcollins View Drop Down
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Thanks Ted, excellent and very informative response. So I assume that means my Zeiss Victory T* FL 8x42 with the Lotu Tec has some decent glass in them?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 18:29
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Absolutely!  It is among the very best "no compromises" binos you can buy in the world!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 22:22
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Ditto on the Zeiss FL comments. Some more info to add....
 
The Zeiss FLs are excellent for two reasons. One they do use FL glass in the objectives, as mentioned previously. Second, they use Abbe-Koenig roof prisms instead of the Schmidt Pechan type found in almost all other roof prism binoculars. The "ABK" prism allow higher light transmission values because of their unique design.
 
And just to clarify a bit on what Rifledude posted. The "FL" stands for Fluoride and not Fluorite. The FL "glass" has Fluoride ions dispersed throughout in order to help reduce chromatic aberration and thus produces sharper and, arguably, brighter images. The only consumer optic that I am aware of which uses "Fluorite" is the Kowa Prominar 88 mm scopes. Everything else that is out there uses some type of "ED" (Extra low Dispersion) glass. There is a measuring system to differentiate between different types of ED glass used in the various binocular designs but I sincerely doubt the manufacturers would let that information become public. Simply stating that a binocular utilizes ED glass gives it more marketing value but does not necessarily tell you the quality level of the ED glass utilized.
 
Also, as mentioned in the above post, it takes more than just ED glass in the objectives to reduce color fringing and produce a sharper image. The ED glass has to be matched with the specific optical design in order to get optimal results. I had a discussion with one particular manufacturer rep last year about why they did not utilize ED glass in one of their binos. His response was along the line that in order for the ED glass to be truly effective the physical length of the binocular (or maybe focal length) needed to be a certain amount. ED glass could be utilized in the design but the design would not be taking full advantage of what the ED objectives had to offer.
 
Also, for what it is worth, I don't put any faith in "HD" when it comes to describing objective materials. HD pretty much just stands for high definition and is more of a marketing term to tap into the thought processes associated with it. HD does not, in any way, guarantee the use of any type of ED glass in the binocular design.
 
Hope this helps.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2010 at 23:10
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Originally posted by FrankD FrankD wrote:

 
Also, for what it is worth, I don't put any faith in "HD" when it comes to describing objective materials. HD pretty much just stands for high definition and is more of a marketing term to tap into the thought processes associated with it. HD does not, in any way, guarantee the use of any type of ED glass in the binocular design.
 
Hope this helps.
Frank,
 
Excellent clarification.
 


Edited by Bird Watcher - August/17/2010 at 23:14
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2010 at 07:21
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Originally posted by FrankD FrankD wrote:

The "FL" stands for Fluoride and not Fluorite.


Yeah, I get the "fluoride" and "fluorite" thing mixed up.Bucky

"...you say tomato, I say tomahto..."
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2010 at 09:47
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Ted,
 
Glad you didn't take me the wrong way. I mixed them up previously as well.
 
Brock's post on cloudy nights is very good. Edz tends to get more technical than I can follow....Smile
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2010 at 10:48
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Originally posted by FrankD FrankD wrote:

Edz tends to get more technical than I can follow....Smile
 
You & me both. Perhaps that's why he is known as the Pro fess sir.
 
 
 


Edited by Bird Watcher - August/18/2010 at 16:11
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2010 at 18:18
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Originally posted by tpcollins tpcollins wrote:

Thanks Ted, excellent and very informative response. So I assume that means my Zeiss Victory T* FL 8x42 with the Lotu Tec has some decent glass in them?

Most likely. I think you ought to send it to me so I can check it out and make sure you'll like it.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/19/2010 at 07:31
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Originally posted by Alan Robertson Alan Robertson wrote:

Originally posted by tpcollins tpcollins wrote:

Thanks Ted, excellent and very informative response. So I assume that means my Zeiss Victory T* FL 8x42 with the Lotu Tec has some decent glass in them?

Most likely. I think you ought to send it to me so I can check it out and make sure you'll like it.
 
Thanks Alan, I'll get right on that . . .   :-)
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