Thanks Lee for that excellent interview - informative and very professional while asking all the right questions.
You do us proud!:t:
James
Thank you so much, I really appreciate your kind words.
Lee
Thanks Lee for that excellent interview - informative and very professional while asking all the right questions.
You do us proud!:t:
. We heard that the SF is now in its production phase and a number were sold already this afternoon, when I left 12 pieces were already sold.
Gijs van Ginkel
just noted that it's different then FL and HT, then whats the difference?
higher content of Calcium Fluorite?
Fluorite crystal is very difficult to work with as well, and expensive…
would be nice with some more info on the Ultra-FL glass,
Dobler says:
"The doublet is made from glass containing calcium fluorite, different from FL and HT but still supplied by Schott and it is very expensive and a challenge to work with as it can break more easily during manufacturing."
and some info from Takahashi web-site:
"..Other telescope manufacturers may claim that ED (Extra-low Dispersion) glass is the equivalent of fluorite or that their older designs will work as well. Unfortunately, they are not being honest. While ED and fluoro-crown lenses can achieve Abbe-coefficients approaching fluorite, they tend to absorb more light in the visible spectrum. This means that fluorite yields a brighter, higher contrast image. Leica, Zeiss, and Kowa have all gone to fluorite in their spotting scopes and telescopes to achieve the maximum performance levels their customers demand. Most of them previously used ED glass. Obviously, they know the difference between fluorite and ED. You will too. ...
"
---
"To call lenses made of fluoro crown glass fluorite lenses is misleading and is a marketing attempt to sell on the back of the outstanding performance/ reputation of telescopes which used Calciumfluorit elements such as the Takahashi FS-102, FS-128, FS-150, the Vixen 102 and Calciumfluorit doublets of current production."
http://www.iceinspace.com.au/forum/archive/index.php/t-121155.html
The statement was 'glass containing calcium fluorite' so clearly not pure fluorite crystals.
Excellent interview, much appreciated. Thank you, Troubador!
Great interview, Lee. :t:
I appreciate it, greatly !
Lee, thanks a lot for this interesting interview! I agree that Herr Dobler and Herr Seil have taken the challenge of a very ambitious project, and surely something great has been achieved. Most notably an increase in field of view with, at the same time, high edge sharpness, that's something quite remarkable!
The doublet lens apparently contains one lens element made of CaF2, so it is a classical ED. These CaF2 lenses are not only hard to shape, but also difficult to coat, since not all of the anti-reflex layers are sticking well on that material. I guess this is an air-spaced doublet, with "super-thin" lens elements, one of them made of CaF2 - let's hope it won't break upon a strong mechanical impact.
I do not quite understand that explanation for the "Absam-ring", caused by a "kind of field stop" to reduce aberrations like coma. A field stop would affect the field of view, not the sharpness, and the effects of any other kind of stops should increase with the angle, thus affect the edges of field. But the Absam-ring is something that shows up in between. I would have guessed that it was a higher order field curvature effect, but anyway ...
Regarding the globe effect, note that Mr. Dobler claimed 5-10% of the users being affected by that effect. "Affected" may refer to more serious reactions than just noticing the effect. I would guess that, with distortion-free optics, at least 40% of the users would notice the effect, but certainly less than 10% are feeling seriously disturbed by that effect. It is great to know that they have taken the side effects of low-distortion serious and that they have conducted tests about them. I would be very much interested in the test results they have got, to compare them with those theoretical and simulation studies I have published a few years ago.
Cheers,
Holger
Lee,
Thanks for the interview. A good read. Interesting to hear the take of the product manager and gain some insight into their thinking.
Holger,
I share your thoughts on the "Absam ring" explanation. It would be nice to hear a bit more about it, since the field-stop explanation does not sound quite right.
Incidentally, I'm a bit annoyed by the "Absam" part of the term that has gained hold on these forums. It was probably coined by Brock in his crusade against the RB-effects of the Swarovisions, but the phenomenon it describes I first saw in Nikon's SE 10x42 which I got in 1996 and still have. It has very good edge of field sharpness, but a little bit inwards from the edge the sharpness falls off before increasing again, very much like in the Swarovisions. So, for historical correctness, credit should be given to the inventors of this anomaly and it should be called the "SE ring," unless an even earlier precedent is found. I do not know if this effect is equally visible in the 8x32 SE, since that model I have not thoroughly tested or viewed with.
Kimmo
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
I guess this is an air-spaced doublet, with "super-thin" lens elements, one of them made of CaF2 - let's hope it won't break upon a strong mechanical impact.
Cheers,
Holger
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
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.
Gijs
The doublet lens apparently contains one lens element made of CaF2, so it is a classical ED. These CaF2 lenses are not only hard to shape, but also difficult to coat, since not all of the anti-reflex layers are sticking well on that material. I guess this is an air-spaced doublet, with "super-thin" lens elements, one of them made of CaF2 - let's hope it won't break upon a strong mechanical impact.
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
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.
I look forward to Dennis's authoritative review.