What does T* FL with LotuTec really mean? (1 Viewer)

Is this Zeiss' version of HD glass or not? Thanks.

tpcollins said:

Is this Zeiss' version of HD glass or not?

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Hello TP,

Yes, it is.

Happy bird watching,
Arthur

more info here, and more has been written also on this forum (but you need a good search on keywords )

tpcollins said:

Is this Zeiss' version of HD glass or not? Thanks.

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Keep in mind that "FL" and "HD" are meaningless marketing terms used mostly to conceal what kind of glass is really used.

Only Minox, to its credit, comes right out and tells us that SCHOTT N-PK52A is the ED glass used in its so-called APO binoculars. It's almost certain that Zeiss also uses SCHOTT glass since SCHOTT AG and Zeiss AG are two parts of the same company. If Leica and Swarovski are sourcing their glass in Europe they're probably buying from SCHOTT also.

The current SCHOTT catalogue lists three glass types that could be called "ED":

N-PK51 with a Vd number of about 77
N-PK52A with a Vd number of about 81.5
N-FK51A with a Vd of about 84.5

None of these are very close to the "gold standards" of low dispersion materials, which are Fluorite (CaF2) and Ohara FPL53, both with Vd of about 95 (the higher the Vd, the lower the dispersion). The most likely candidate for "FL" glass is N-FK51A, since it's a fluoride containing glass with the highest Vd number of anything in the current SCHOTT catalogue, except Fluorite.

BTW, the type of ED glass only tells us what CA correction is potentially possible. The mating glass types and the total design will determine whether that potential is reached. I suppose that's one good excuse for not revealing the ED glass type, so that consumers aren't tempted to rely solely on the Vd number as a shorthand predictor for quality.

Henry,

Thanks for the info. Here's a link to Schott optical glasses.- http://www.schott.com/advanced_optics/english/our_products/materials/data_tools/index.html.
When one looks at the blue transmission values of some flint glasses it's easy to understand why many bins have a yellow tint. Also apparent how BaK4 prisms cost a few percent transmission.

John

Thanks for the link, John. That's a useful tool.

Henry

tpcollins said:

Is this Zeiss' version of HD glass or not? Thanks.

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To answer your original question, T* refers to Zeiss proprietary lens (not to be confused with prism) coatings. Going back to when multi-coatings were a new technology, every optics company came up with their own trademarked name for their version of multi-coatings. Of course, T* multi-coatings have continued to evolve, but Zeiss will only use the T* logo on their finest optics. On top of that (literally), Zeiss now uses an additional hydrophobic lens coating they call LotuTec, which shed water droplets, making it easier to clean them in wet field conditions. As others have already addressed, the letters FL refer to the special Fluoride glass used in the objective group to minimize chromatic aberration.

ED: Is Nikon's "Extra low Dispersion" glass.

FL: Is Flourite glass which is an excellent low dispersion glass

ED was invented and patented and manufactured by Nikon way after flourite was being used, to address an inherent problem with using flourite elements. (Canon has an SD or "Super low dispersion" glass ect and other brands I'm sure have names for thiers.) One inherent flaw to flourite lens elements is that they are very brittle, and prone to cracking in very large elements and in temperature extremes. Zeiss may be using a different type of flourite glass now, or in the application it's used in may be quite durable who knows, but rest assured it has one or more low dispersion elements in it's design. Don't think all the glass is special "HD" glass, more than likely just it's just one element per side, like the objective lens probably.(the lens that would benefit the greatest from lower CA) Lotutec is just a coating on the objectice element to repel water, which in my opinion has to have a negative effect on optical quality if only infintessimally small. It's probably still worth having though since it's easier to clean now.

Agent,

The Nikon glass making subsidiary, Hikari, currently makes three glass types that could be called "ED".

E-FK01, Vd 81.64
E-FkH1, Vd 82.52
E-FKH2, Vd 91.31

All of these are fluor-crown glasses which contain fluoride just like Zeiss "FL" glass. None of them equal Fluorite (CaF2, Vd 95) for low dispersion. The Fieldscopes probably use E-FKH2 because it's the closest to Fluorite, so it has the greatest potential for color correction if the mating elements are well chosen.

Agent47 said:

One inherent flaw to flourite lens elements is that they are very brittle, and prone to cracking in very large elements and in temperature extremes.

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True. Fluorite is also quite a bit softer than most types of glass, so in most designs it isn't used as the front element. And yet, Kowa used Fluorite in their venerable TSN 3/4 scopes, and even after years of use (and abuse) there were hardly any reports of problems with the fluorite lenses.

Hermann

I think most of the supposed problems attributed to Fluorite have been highly exaggerated by the marketers of competing materials, like ED glass. I have a short article (The Truth About the Use of Fluorite as an Optical Material, by Jurgen Pudenz and Alfred Karnapp) that was supplied by Zeiss in defense of the use of Fluorite in its APQ astronomical scopes in 1994. Most of the usual issues are addressed like water absorption, production costs, fragility to thermal shock, etc. Almost all the problems can be solved in one way or another except production cost. In the last ten years glass has been developed (Ohara FPL53) that is essentially equivalent to Fluorite. A lower cost equivalent, rather than serious flaws, is probably what explains the gradual disappearance of Fluorite in astronomical refractors until now there are only a few; one Stellarvue and two Takahashi models, and the 88mm Kowa spotting scopes, perhaps a few more. I can't think of any example of a small binocular that ever used Fluorite in the objectives.

Henry

afterthought... I think the term "HD" is funny. Just because t.v.s now have higher resoloution and they call them "HD", now HD is a buzzword that lots of companies use. I've seen sunglass companies and many others using it as well. Just like past buzzwords like "titanium" or the number "2000" for some reason. Although while it's slightly insulting to consumers intelligence, it's probably a pretty effective marketing term.