An informal and unofficial interview with
Gerold Dobler, Director, Carl Zeiss Sports Optics Product Management
Herr Dobler, thank you for making yourself available for this interview. Could you tell us a little about your career in optics leading up to you joining Zeiss Sports Optics?
I actually started to work with optical companies in 1992 / 93 as an advisor but then I was asked by Gerhard Swarovski in 1997 to join the company after working with them as a consultant. I was their first product manager. The idea was to help them build a presence in the birding market because they only had a strong connection with the hunting market and since I am a birder I could help them out with this. I was the only product manager in Swarovski at this time and worked on several projects including the EL.
I worked with Swarovski until 2008 when I joined Leica to help develop their sports optics and in particular the Magnus rifle scope range and the open bridge Perger porro Geovid. Herr Perger was behind the technical design of both the first Geovid and the new one, but for the current open-bridge model, the overall concept and industrial design was my responsibility.
In 2011 Herr Schmidt asked me to join Zeiss to re-introduce Zeiss into the birding world by developing a new birding binocular that would be better than the EL SV, and also suitable for butterfly watching and nature observation in general. It was felt Zeiss had become too concentrated on hunting and needed help to approach the nature observation market again and since I had done this for Swarovski, Herr Schmidt thought I was the right person to do this for Zeiss.
One of the key members of the SF team passed away last year. Would you tell us who he was, something about his previous work and how he contributed to SF?
One of the people who followed me from Swarovski was Konrad Seil, who did the optical design the original EL and for the Magnus scope at Leica. It was Konrad who also worked out the optical design for the SF based on my concept.
Konrad took my ideas and developed them into precise optical designs and this is what he did with SF. Several optical designers have since said that they did not think it possible to achieve what we have done with the objective lens design on SF and reach the quality of image that we have, but Konnie always took my concepts absolutely seriously and worked to make them succeed and his contribution was crucial to the success of the SF.
How does the SF optical system compare with FL & HT, and with Ultravid & EL SV
Actually the SF optical system is different from every other binocular that we know of today. The concept includes an eyepiece that adds weight to the design due to giving a wider field of view and also sharpness up to close to the edge. This weight increase is unavoidable if you want to achieve this performance and the only way to compensate for this is to take out weight from the objective system. This was the idea and the challenge.
The solution was a super-thin achromatic doublet objective weighing much less than the triplet in our FL and HT, and also the EL SV, in combination with a focusing lens that is actually designed not only as a focuser but also a critical part of the objective system. The doublet is made from glass containing calcium fluoride, 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.
These lenses are even thinner than those in FL and HT and brought us a very significant weight reduction which compensated for the extra weight in the eyepiece.
There has been a report of an effect in SF whereby there is an area of slight softness of the image between the centre of the field of view and the edge. What can you tell us about this?
Yes there is this effect but it will not be seen during normal viewing and it cannot be seen at all in the 8x. It is caused by apertures within the optical system, they are like field-stops so to say, and they are there to control different optical aberrations for example coma. It is always a compromise in optical systems that you improve one situation but you risk making something else worse. So we have chosen a balance between control of aberrations and the appearance of a very slight softness in a ring between the centre and the outside that will not normally be detected. By a very few people, looking very hard, in some circumstances, it is possible the effect might be seen in the 10x, but in any normal viewing by the majority of people, they would never notice it was there and even in the area where this occurs the binocular is still very competitive with other premium binoculars as far as sharpness is concerned. We are very happy indeed with result that we have got.
SF is named after the Smart Focus concept. This has given some people the impression that the focus speed should be quite fast or even that it has a dual speed focuser, but actually, although SF is faster than EL SV, it is a little slower than HT, so what is Smart about it and did you consider giving SF a dual speed focuser?
Well, it is actually possible to have focus that is too fast for most users, because you overshoot the point of focus too many times. SF is definitely a compromise but it is significantly faster than EL SV and still allows very good control of the point of focus and we are very happy with the result. We asked people in the market about dual speed focusers and most of those we asked do not like the idea of it. They just don’t want it. Also, to do it well, a dual speed focuser adds significant weight to the bins which is definitely what people do not want.
Low weight has been a priority with SF although Zeiss appears to have reacted to market pressure by moving away from the GRP body of FL to a magnesium alloy. Do you think that you have gone as far as it is possible to go with weight reduction while staying with a metal body? If so, what do you think might be the next step?
Magnesium alloy is used more and more for different applications and the supply is getting better so the price has come down a little from previous times and a full metal housing has a very strong image in the premium market and to be practical it does provide a certain ruggedness. It’s a good solution, it has a good image and a reasonable price, so I expect it will be the standard material in the premium sector for some years.
I understand your target of 800 gram maximum for SF and in that context you have done well to keep it to 780 grams. However at 173 mm long, it is 8% longer than the EL SV despite only having a doublet objective. Is this extra length due to the extra bridge?
It has several reasons. We wanted a larger open bridge area to provide more space for the hands for a good grip than some other bins. I believe the extra length is not such a disadvantage compared with ergonomic advantages. Improved ergonomics were a big factor in the concept of SF.
Now for our final question. With SF you have tried to achieve a balance between a flat field, large field of view, sharpness up to the edge of the view and minimising the well-known effect called ‘rolling ball’. How successful have you been with these four desirable attributes?
We found a good balance between these different things and especially in the control of the so-called rolling ball or globus effect that affects between 5 and 10% of people. We contacted some of these people and asked them to try different binoculars having different levels of field-flattening and we came up with a value that gave the best balance between field flatness and control of the globus effect. This means SF is not quite so flat-field at the very edge but it is nearly so, and from what those people told us almost everybody should be able to enjoy SF without noticing any globus effect.
Will the extra wide field of view also be a feature of the SF 32 mm that is surely going to follow the 42?
Well, I cannot say anything about a specification for any model that we might develop, but it is clear that a wide field of view is a successful part of the SF concept so I would expect this to be a feature of any model developed using the SF concept.
Herr Dobler, thank you very much.
