Fluoride Glass, Fluoride Coating, where, what? (1 Viewer)

[Ted Y.]

What parts of a binocular are made from fluoride: the prisms, all lenses, some lenses?
What about the coating? It is the same fluoride?

One must care about this?

Update:
Can be about fluorite parts in binoculars?
From Zeiss website: fluoride lenses.

From Maven website: fluorite glass


I will stop trust everything about binoculars on Internet.

 

[Maljunulo]

First, we have to understand the difference between fluorite and fluoride.

Flourite is a mineral (CaF2) and it is used for elements in well-corrected (and expensive) optics.

Flouride is the term for any compound of fluorine. (Including fluorite, which is Calcium fluoride)

Some fluorides are used as additives, which are added to optical glasses during the melt.

I know of no instances of fluorides in optical coating, but this may just be my ignorance.

Many sales and marketing divisions of optical firms, and reviewers, neither grasp the distinction, or seem to care to.

Hence almost total confusion among the public.

 

[james holdsworth]

What parts of a binocular are made from fluoride: the prisms, all lenses, some lenses?
What about the coating? It is the same fluoride?

One must care about this?

Which binocular?

 

[JoeGBirder]

The prisms are made from fluorite, which helps reduce blur (or, to be fancy, chromatic abberation.) I think.
I should also mention that not all binoculars have fluorite prisms, it depends on the model. I'm not sure whether or not you were aware of this, so I added just in case.
-joe

 

[sillyak]

The prisms are made from fluorite, which helps reduce blur (or, to be fancy, chromatic abberation.) I think.
I should also mention that not all binoculars have fluorite prisms, it depends on the model. I'm not sure whether or not you were aware of this, so I added just in case.
-joe

I am unaware of any Fluorite prism. It's almost always in the objective group. Some Canon lenses have it further down the lens from the objective.

Fluorite is a crystal which has very low dispersion, which can reduce chromatic abberation in a well designed optic. High quality glass like FPL-53 is very close to Fluorite, but not quite as good, however it is easier to work with.

I am unaware of any binocular that has a Fluorite element, although it is possible as most binocular makers do not disclose glass types.

Kowa uses a Fluorite objective element in some spotting scope models. Currently on the 99, 880 and 550.

Canon uses it in some of its lenses, mainly super expensive super telephotos.

Takahashi uses it in many of its telescope objectives. There are also a handful of small volume high end telescope makers that use it.

There is only one manufacturer of optical Fluorite in the world. Considering it's harder to grind, polish and coat, and that glass like FPL-53 can almost match it, it isn't used widely. Mostly in very high end optics larger than binoculars.

Some binocular marketing literature, and uninformed binocular users, interchange fluorite with fluoride. Fluorite is a crystal that is essentially the highest performing optical glass. Fluoride is any one of a number of compounds that contain Fluorine, which is also used in coatings and in the melt of some optical glass.

 

[JoeGBirder]

I am unaware of any Fluorite prism. It's almost always in the objective group. Some Canon lenses have it further down the lens from the objective.

Fluorite is a crystal which has very low dispersion, which can reduce chromatic abberation in a well designed optic. High quality glass like FPL-53 is very close to Fluorite, but not quite as good, however it is easier to work with.

I am unaware of any binocular that has a Fluorite element, although it is possible as most binocular makers do not disclose glass types.

Kowa uses a Fluorite objective element in some spotting scope models. Currently on the 99, 880 and 550.

Canon uses it in some of its lenses, mainly super expensive super telephotos.

Takahashi uses it in many of its telescope objectives. There are also a handful of small volume high end telescope makers that use it.

There is only one manufacturer of optical Fluorite in the world. Considering it's harder to grind, polish and coat, and that glass like FPL-53 can almost match it, it isn't used widely. Mostly in very high end optics larger than binoculars.

Some binocular marketing literature, and uninformed binocular users, interchange fluorite with fluoride. Fluorite is a crystal that is essentially the highest performing optical glass. Fluoride is any one of a number of compounds that contain Fluorine, which is also used in coatings and in the melt of some optical glass.

google fails me once again 😞
i don't actually know any of this except that it could help prevent blur. lol
sorry

-joe

 

[John A Roberts]

Hi Ted (post #1),

See a diagram from Zeiss about the SF x42. The fluoride glass is in the objectives, as is also the case when it’s used in other binoculars.
(but be aware that there’s another version of the diagram that’s incorrectly, seemingly randomly, labelled).

In this case, all 3 of the SF x42 objective lenses use fluoride (both of the fixed lenses and the focuser).
See the second last paragraph on page 4, of Lee’s interview with the designer of the SF x42 Gerald Dobler.


John

 

[Tringa45]

In this case, all 3 of the SF x42 objective lenses use fluoride (both of the fixed lenses and the focuser).
See the second last paragraph on page 4, of Lee’s interview with the designer of the SF x42 Gerald Dobler.

John,

I think there was possibly a misunderstanding here and consider it highly unlikely that all three objective elements of the Zeiss SF contain fluorides.
AFAIK fluorides are only used in crown glasses of extremely low dispersion, e.g. Schott FK or Ohara FPL.

Normally a doublet objective would consist of a converging +ve. element of crown glass (low dispersion but also low refractive index) and a diverging -ve. element of flint glass (higher dispersion but often higher refractive index). They would be combined to have a nett converging effect while ideally minimizing spherical aberration and reducing colour errors.

The Zeiss SF42 would appear to have a cemented doublet objective in Steinheil configuration with the -ve. flint element in front and a +ve. (fluoride crown?) element behind. It would, of course, be of advantage to use fluoride crown for the single element +ve. focussing lens.

John

PS:- Technische Eigenschaften optisches Glas | SCHOTT Scroll down for Abbe diagram.

 

[Binastro]

Takahashi 22x60 binocular.

B.

 

[John A Roberts]

Hi John (post #8),

I too had doubt, but considering the source I thought it worthwhile to quote.

For a cross section view of the lenses, see a diagram of the SF (and HT) from 'The Art of Precision'.
It's a 60 page brochure from the SF's introduction, see at: Zeiss Victory SF and HT - technical data, diagrams, cutaway views and more


John

 

[Tringa45]

Takahashi 22x60 binocular.

Probably unique in having fluorite elements in the objectives and, allegedly with some outstanding optical qualities.
Nevertheless, it had a miserable AFoV similar to that 20x60 Pentax you mentioned!

John

 

[henry link]

I think the Takahashi 22x60 just cobbled together two Fluorite doublet objective lenses from the FS-60C with an ordinary 7x50 Porro body with inexpensiv Kellner eyepieces. It really didn't even need Bak4 prisms since the objectives were f/5.9.

 

[henry link]

Hi John (post #8),

I too had doubt, but considering the source I thought it worthwhile to quote.

For a cross section view of the lenses, see a diagram of the SF (and HT) from 'The Art of Precision'.
It's a 60 page brochure from the SF's introduction, see at: Zeiss Victory SF and HT - technical data, diagrams, cutaway views and more


John

I have to agree with Tringa45 about the glass types in the SF objective. All three lenses in the SF objective group can't possibly be "fluoride glass". That wouldn't make a workable objective. Almost certainly the front negative lens is some sort of glass with a low Abbe # to match the other two positive lenses with high Abbe values.

It's also curious to me that the SF objective design is represented as an innovation in that interview. Konrad Seil had already done a few almost identical designs (except for glass types) during his years at Swarovski, like the original EL and some SLCs in the 1990s.

Henry

 

[John A Roberts]

The sentence in question is in the context:
' . . . Dobler wanted to control the weight but he also wanted a wide field of view, with good eye relief, both factors increasing the weight of the eyepiece. But by removing one lens from the objective group, he could keep the overall weight within targets, and also re-balance the binocular in the way he wanted . . . Dobler set about simulations (and) . . . Step by step, by changing lens designs and glass-types, including specifying very special fluoride- doped glass for the two objective lenses and the focusing lens, the simulations gradually resolved towards the successful final design.'


Perhaps what was meant by the sentence was:
'Step by step, by changing lens designs and glass-types, including trying very special fluoride- doped glass for (all three objective lenses) . . . , the simulations gradually resolved towards the successful final design.'


John

 

[Binocollector]

If somebody had a link to the original text in German I could tell you if it was a mistake in the translation or something like that. I couldn't find it so far on my own.
I only found this:

An interview with Gerold Dobler, leader of the SF design team

While travelling in Germany recently I had the opportunity to conduct an informal and unofficial interview with Herr Dobler. We agreed that this would not be centred around the marketing claims for this binocular but would consist of me asking Herr Dobler to comment on a number of issues raised...

www.birdforum.net

quote: The doublet is made from glass containing calcium fluorite

 

[Maljunulo]

quote: The doublet is made from glass containing calcium fluorite

I cannot find any reference to calcium fluorite in a quick search, what is it?

I can only find calcium fluoride. (CaF2)

 

[Binocollector]

Probably a typo in the interview. Just quoted it in reference to the question how many objective elements had that type of glass.

 

[Maljunulo]

Thanks.

 

[Binocollector]

However now that I think about it -- even that question is not clearly answered when thinking about it -- "The doublet is made from glass containing calcium fluorite"
It doesn't explicitely state that both elements contain it.
And btw -- I guess the typo was made by moderator Troubador aka Lee who typed down the recorded interview if I understood the post correctly.
Also -- "Flourit" and "Flourid" is pronounced about the same in German. The interview might have been in English though so I cannot say how the typo came about.

 

[JoeGBirder]

this is too confusing for my small brain, sorry.

-joe