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An interview with Gerold Dobler, leader of the SF design team (1 Viewer)
- Thread starter Troubador
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Vespobuteo
Well-known member
Hi VB
The lenses referred to contain calcium fluorite as an addition to the chemical composition of the glass so they are not pure crystals.
Zeiss FL and HT also used this type of glass. The SF 'fluorite' glass is different from HT but I don't know in what way, but I suspect that it has to do with the objective system being a doublet + focuser system instead of the triplet of the HT, rather than any enhancement of the low dispersion characteristics which are already excellent in HT.
Lee
Thanks Holger
Regarding the Absam ring, I think Herr Dobler was using English very precisely by saying 5-10% are affected by it and not simply perceiving the effect.
And it was interesting that the chosen level of distortion was arrived at not simply by calculation and theory, but aided greatly by empirical observations by people, and that this method brought SF so close to the line on your graph postulating an optimum distortion.
As always this is a compromise between the desired field flatness and the freedom from perceived rolling ball.
Lee
Hej Kimmo
Thanks for your welcome to the interview.
We will see if other observers and commentators begin calling this effect the SE Ring.
There is a saying that there is nothing new under the sun, so I wouldn't be at all surprised if you could find this effect in bins prior to the SE.
Lee
Gijs van Ginkel
Well-known member
Vespobuteo, post 22,
The SF's were delivered on the spot and not preordered.
Lee,
I understood from Dobler during his DBA lecture that Konrad Seil and he himself were inspired by the Erfle and the Ethos design eypieces to obtain a large aberration free FOV. Therefore the SF eyepiece, which is an excellent piece of work, could , as far as I am concerned, get the name of Seil-Erfle-Dobler (SEB-eyepiece for those who like abbreviations) eyepiece to honor the work of the designers.
Dobler also told me when asked, that all problems with the focusser, flare and eyepieces were resolved in the production process. The grey rubber mantle, althogh very thin was shown to be very shockresistant considering the projected graphs. Color reproduction of the SF should be excellent and comply perfectly with the DIN-standard for it. At the Dutch Birdfair I noticed that the SF had a tiny advantage of the Swarovski SV as far as the reproduction of whites is concerned, but the difference is very small and it will probably not be observed by the great majority of observers.
Dobler also told that a group of approx. 20 people were involved in the SF development and that the whole process took about two years. Stefan Bühring told me at the Dutch Birdfair that it took 3 years, but what is a year in view of eternity.
Gijs
The SF's were delivered on the spot and not preordered.
Lee,
I understood from Dobler during his DBA lecture that Konrad Seil and he himself were inspired by the Erfle and the Ethos design eypieces to obtain a large aberration free FOV. Therefore the SF eyepiece, which is an excellent piece of work, could , as far as I am concerned, get the name of Seil-Erfle-Dobler (SEB-eyepiece for those who like abbreviations) eyepiece to honor the work of the designers.
Dobler also told me when asked, that all problems with the focusser, flare and eyepieces were resolved in the production process. The grey rubber mantle, althogh very thin was shown to be very shockresistant considering the projected graphs. Color reproduction of the SF should be excellent and comply perfectly with the DIN-standard for it. At the Dutch Birdfair I noticed that the SF had a tiny advantage of the Swarovski SV as far as the reproduction of whites is concerned, but the difference is very small and it will probably not be observed by the great majority of observers.
Dobler also told that a group of approx. 20 people were involved in the SF development and that the whole process took about two years. Stefan Bühring told me at the Dutch Birdfair that it took 3 years, but what is a year in view of eternity.
Gijs
Gijs
Thank you indeed for this update which are a nice addition to the interview.
Lee
Holger and Gijs
This characteristic of CaF2 lenses has been taken into consideration by Herr Dobler and Zeiss looked carefully for a better rubber armour to help with this.
The armour fitted to SF is actually not quite solid, there are 'ribs' moulded into the underside of the armour, separated by small air spaces. Although solid armour might feel a bit more tough to some people this SF armour is significantly better at absorbing mechanical shocks.
Lee
Lee,
Then it seems that the new design was a tradeoff between a higher risk of damage potential caused by the new objectives vs an overall lighter weight for the binocular along with moving the balance point of the binocular back toward the oculars?
Do you know much weight was saved by not using the triplet objectives the HT/FLs used?
Bob
Hi Bob
Nice to hear from you. I am not a spokesman for Zeiss so what follows is my understanding based on conversations with Her Dobler.
Zeiss do not consider the fragility of the objectives to be a great concern due to their experience in using this material in the FLs and HTs and felt confident in using it even in this ultra-thin design. Biinoculars are nothing more than a truck-load of trade-offs anyway and this includes the weight saving vs robustness question although material choices can help this.
However, mindful of not only the objectives but also of the weight saving done throughout the SF they felt that looking for additional protection was a natural thing to do and also part of an organic process of improvement from FL to HT to SF. So they looked for cleverly designed armour that was also economical with regard to weight.
I'm sorry I don't know the precise weight saving by dumping one objective and thinning the other two.
The final machined magnesium alloy body, prior to mounting of lenses, prisms and other stuff is a thing of beauty and feels as light as an egg-shell and yet is really robust.
Lee
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Gijs van Ginkel
Well-known member
Ceasar,
Dobler emphasized over and over that the goal was: a lighter binocular than the Swar. SV, a larger FOV, a lighter weight (which came down to 780 grams for the 8x and 10x SF's) , improved ergonomics (better grip due to more space for the hands (the SF advertising book says 15% more then the SV), improvement of the balance by bringing part of the bodyweight to the 7 lens eyepiece, which has a weight of 150 grams versus 130 grams for the 3 lens objective. The objective consists of a doublet and a separate focussing lens which is part of the objective group, very close focus (1,5, m), fast focus (1,8 rev. from close focus to infinity)
To compare it with the HT: the eyepiece system of the HT weighs 90 grams and the objective system weighs 208 grams.
Zeiss also tried to give the SF a high transmission of 92%, therefore the Schmidt-Pechan prisms have a 70 layer dielectric coating. The field flattener is designed so as not to yield a fully sharp field up to the very edge to decrease the globus effect. On my question whether the resolution is constant over the whole FOV Dobler told that this was the case. A special case was designed for the SF for quick and easy access to the binocular.
NB. These are not my test results, but a summary of the advertising book, Zeiss supplies with the SF.
The book says over and over that the SF is the world's best birding and wildlife observation binocular: in short simply the best (quotations, not my words).
Dobler emphasized frequently that the SF was specially designed for birders and wildlife observation.
Gijs
Dobler emphasized over and over that the goal was: a lighter binocular than the Swar. SV, a larger FOV, a lighter weight (which came down to 780 grams for the 8x and 10x SF's) , improved ergonomics (better grip due to more space for the hands (the SF advertising book says 15% more then the SV), improvement of the balance by bringing part of the bodyweight to the 7 lens eyepiece, which has a weight of 150 grams versus 130 grams for the 3 lens objective. The objective consists of a doublet and a separate focussing lens which is part of the objective group, very close focus (1,5, m), fast focus (1,8 rev. from close focus to infinity)
To compare it with the HT: the eyepiece system of the HT weighs 90 grams and the objective system weighs 208 grams.
Zeiss also tried to give the SF a high transmission of 92%, therefore the Schmidt-Pechan prisms have a 70 layer dielectric coating. The field flattener is designed so as not to yield a fully sharp field up to the very edge to decrease the globus effect. On my question whether the resolution is constant over the whole FOV Dobler told that this was the case. A special case was designed for the SF for quick and easy access to the binocular.
NB. These are not my test results, but a summary of the advertising book, Zeiss supplies with the SF.
The book says over and over that the SF is the world's best birding and wildlife observation binocular: in short simply the best (quotations, not my words).
Dobler emphasized frequently that the SF was specially designed for birders and wildlife observation.
Gijs
Gijs just to be clear, when you say 130 grams for the 3 lens objective do you mean the SF objective which is a doublet + focus lens system??
Lee
I am not a chemist but calcium fluoride is CaF2.
The mineral fluorite, fluorspar is often deeply coloured due to impurities.
These crystals and glasses are difficult to work with and coat especially multicoat.
Many special glasses must be immediately coated when made as they quickly tarnish.
Thin elements are difficult to make, but are less susceptible to heat changes.
Some tea glasses are made very thin of ordinary glass as they can withstand repeated boiling water shock. A thicker glass would crack.
The Absam, SE ring effect, I think exists in photographic lenses over 100 years old, I will check, but if memory serves me correctly it is very old.
I do hope that if the SF has Erfle eyepieces is does not show any ghost images at all, as older Erfle eyepiece binoculars such as Swift HR5, Soviet 6x24 and many other are plagued by ghosts from bright light sources.
Multicoating does not help much, but careful design might.
The mineral fluorite, fluorspar is often deeply coloured due to impurities.
These crystals and glasses are difficult to work with and coat especially multicoat.
Many special glasses must be immediately coated when made as they quickly tarnish.
Thin elements are difficult to make, but are less susceptible to heat changes.
Some tea glasses are made very thin of ordinary glass as they can withstand repeated boiling water shock. A thicker glass would crack.
The Absam, SE ring effect, I think exists in photographic lenses over 100 years old, I will check, but if memory serves me correctly it is very old.
I do hope that if the SF has Erfle eyepieces is does not show any ghost images at all, as older Erfle eyepiece binoculars such as Swift HR5, Soviet 6x24 and many other are plagued by ghosts from bright light sources.
Multicoating does not help much, but careful design might.
Hermann
Well-known member
Kowa has been using CaF2 lenses in the objectives of their top scopes for many years now, staring with the venerable TSN3/4. I haven't heard of any problems at all with these lenses.
Hermann
Hermann,
You are right about the Kowa scopes. I don't think I've heard of a single one where the lens would have broken, but I have seen a few of the TSN3 and 823 models that have been just about battered to pieces otherwise, due to very rough use. So yes, it would be rather a surprise if lens durability would become an issue.
Kimmo
You are right about the Kowa scopes. I don't think I've heard of a single one where the lens would have broken, but I have seen a few of the TSN3 and 823 models that have been just about battered to pieces otherwise, due to very rough use. So yes, it would be rather a surprise if lens durability would become an issue.
Kimmo
Canon have used it in photographic optics for many decades. Nikon have started using it, along with their ED and super ED glasses. And the lenses are not even protected with rubber armour, so shock will be worse. This link is interesting:
http://cpn.canon-europe.com/content/education/infobank/lenses/fluorite_aspherical_and_ud_lenses.do
Canon claim a flourite element takes four times as long to grind, adding to the cost, although having only two objective elements will reduce costs a bit.
Very interesting thread by Lee. :t:
I look forward to Dennis's authoritative review.
Vespobuteo
Well-known member
Interesting that Nikon finally decided to use Fluorite in camera lenses. It seems to save a lot of weight in long telephoto lenses. Canons latest lenses are so much lighter than nikons corresponding ED-versions. Though the prices have become ridiculous on the new versions…
seems to be a lot of work though, making lenses:
http://www.youtube.com/results?search_query=canon+lens+production
wouldn't it be easier to sell sausages instead?
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bh46118
Well-known member
Like Dennis or not, he will step up to the plate and buy cutting edge glass that a lot of other only talk about. What he does with them after he buys them ?:-O
If the SF is by consensus of many credible opinions a true advancement over the latest SV, then I will more than likely buy one myself. It's all totaly speculatively at this point.
If the SF is by consensus of many credible opinions a true advancement over the latest SV, then I will more than likely buy one myself. It's all totaly speculatively at this point.
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