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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Interview with Zeiss Senior Optical Scientist (1 Viewer)


Staff member
Continuing my series of interviews with people in the optics world, this time I have been lucky that Thomas Steinich of Zeiss has been willing to donate his time and take part.

Troubador: Herr Steinich please tell us your official job title and how long you have been in this job.

Thomas: Senior Scientist, Optical Design, 14 years.

Troubador: Please tell us about your education, qualifications and where you lived as a child.

Thomas: I was born in Stollberg / Erzgebirge in 1980. We moved to Crailsheim (a small town in-between Stuttgart and Nürnberg) in 1989 some months before the fall of the wall. I finished my school-time in Crailsheim and started university in 2000. My first degree is in Applied Physics from the University of Weingarten and I continued to a Master of Science in Optical System Engineering. During that time, I spent one year at the Fraunhofer Institute for Physical Measurement Techniques in Freiburg and half a year at the Swinburne University of Technology in Melbourne. The first contact with ZEISS was during my Master thesis in 2006 which I finished about wave-front analysis at ZEISS Semiconductor Manufacturing Technology.

Troubador: Where did you work before joining ZEISS?

Thomas: In 2006 I started working as an optical designer for Schneider Kreuznach. The main topics were imaging optics for industrial and photographic applications.

Troubador: Schneider is very well-known and highly respected in the photographic world. When did you join ZEISS, and what has been your career within ZEISS,

Thomas: After 5 years with Schneider Kreuznach I moved to ZEISS Consumer Products in 2011. At ZEISS I had the chance to get involved in very advanced design projects like anamorphic lenses for cinematography, zoom lenses and of course visual instruments like binoculars, spotting scopes and others. The diversity of products at our business unit is something that I like a lot. So as an optical designer you have the opportunity to design many different products. In 2019 I was announced Senior Scientist which is part of our in-house expert career.

Troubador: Where do you live now and are you married?

Thomas: Together with my wife I have been living in Heilbronn for 12 years now. We like living in the city centre, although it is pretty far away from my office in Oberkochen.

Troubador: What are your favourite things to do when you are not at work?

Thomas: Working as an optical designer means sitting a lot in front of a computer. So in my free time I try to do a little sports to compensate for that. Playing badminton is one of my favourites, but also hiking. Travelling is also very important for us. As we both like being outside in the nature there are many spots around the world that we already visited…..and still many, many spots left to visit. Iceland, the island of Réunion and Tasmania were some of our all-time favourites.
And last but not least: Supporting the local ice hockey team “Heilbronner Falken” is also great fun!

Troubador: Do you use binoculars for birding or nature observation? Or not at all?

Thomas: Well, to be honest: I am not a ‘high-power’ user of binoculars, like birders. As you can see from my holiday destinations nature observation is my prime application.

Troubador: How has Coronavirus affected the way you have been working?

Thomas: For me the Coronavirus primarily changed the place of working. I worked completely from home over three months and also supported other business units within ZEISS. Working from home works very well for optical designers. And fortunately, ZEISS had all the IT infrastructure ready for online meetings and remote access to all the relevant data. So the transition was relatively smooth and you can still contact all your colleagues whenever necessary. Now we are more back in the office, but I think working from home will stay part of the working week and will probably increase.

Troubador: What are your normal working days and weeks like (don’t forget regular meetings), and do you work on photo and cinematography, as well as sports optics projects?

Thomas: A standard working week for me is a mixture of meetings, concentrated work at the computer and all kinds of optical questions from different people all over ZEISS Consumer Products. Of course, actually doing optical design is the major part of the workload. But communication is not far behind. For example when you design a new product like a binocular, you have to align your ideas with the mechanical designer, all the colleagues in the production line that are going to build your ideas, the product manager, controllers for budget and manufacturing costs, suppliers like glass manufacturers and many more. And this is true for all kinds of products I am working on from sport optics to cinematographic and photographic lenses. Last but not least: The optical designer is the contact person for any technical optical question and topic that other departments need support with.

Troubador: Please tell us a little about the last 2 projects on which you worked (except SF32 which we will discuss later).

Thomas: Two of my highlight projects are the Harpia spotting scope and the Supreme Prime T1.5/18mm lens. My main target for the Harpia project was to get this amazing imaging performance into a real-life product. Many simulations and theoretical analysis of the assembly process were necessary until we finally came up with this stunning resolution regarding this huge entrance pupil. For our new cinema lenses “Supreme Primes” I designed the ultra-wide-angle 18mm lens with the highest aperture of T=1.5. Looks like everyone wants to have high apertures, directors of photography for cinema and birdwatchers! It was great to have the first working prototype of this lens in your hand after starting with the first rough designs months ago.

Troubador: Do you also work on investigations into existing products and how different aspects of the optics can be improved, including T* and P* coatings?

Thomas: During serial production the optical designer is still responsible for any optical improvements or changes that are necessary. Sometimes assembly and alignment processes can be changed due to new technologies. And this also affects tolerances on individual parts, e.g. lenses.
At ZEISS we have our special experts for coating technologies. So T* and P* reviews and updates are within their responsibility and they give feedback to the optical designer.

Troubador: When you are asked to develop optics for a new sports optics product, what kind of information do you receive to guide you? For example does the brief give targets for light transmission, field of view, eye relief, close focus, length, weight and cost? Are the briefs similar for binoculars and spotting scopes?

Thomas: We have a detailed document with all kinds of information that is necessary to start a new process in optical design. It is very important to thoroughly think about what the important features of a new product are and then the optical designer can think about how to achieve these features. Of course, this document starts from magnification and entrance pupil, defines imaging performance and goes down to size and cost constraints. The criteria for imaging performance, like wave-front deviation, are similar for all visual instruments, whereas size, cost and important features differ a lot. For both binoculars and spotting scopes, ergonomics are very important today. Of course optical quality is vital for both products, with the Harpia scope having been a special challenge to combine the wide field of view at low magnifications with extreme sharpness at maximum magnifications far beyond that of binoculars.

Troubador: Is this concept then tested with software, changing glass types and lens profiles until the targets are met in theory? Can you give an example of how this proceeds?

In general optical design is the process of finding a lens (and in the case of a binoculars also a prism) distribution that is able to a) achieve the given specification that come from the markets needs and b) works as a real-life product and not just on paper. At ZEISS we are in the comfortable position to have all commercial optical design software tools available and even have an in-house software that is specialized on the products we have.
When you start a product design you typically do the bottom-up strategy: you need a deep understanding of the individual parts of your system like objective, prism and eyepiece and then you start with the most simple setup you can think of, so for the objective you can start with a single positive lens. After changing the available variables like radius, glass, thickness you increase complexity step by step, e.g. from a single lens to a doublet – split doublet – even more lenses or aspherical shapes. This process is 100% driven by the designer. The software evaluates and helps you to find the best solution in the trade-off between performance/complexity and cost/mechanical constraints.

Troubador: Then do you verify that the targets are met by producing prototypes and testing them?

Thomas: Yes. Within the software you can verify and analyse all optical criteria perfectly. But real-world prototypes are produced with tolerances and go through a certain alignment and assembly process. Virtual prototyping is already pretty advanced, but hardware prototypes are still necessary to guarantee quality.

Troubador: Do you work according to ISO norms for resolution?

In general, yes.

Troubador: Do you work to ZEISS standards for Modulation Transfer Function, Strehl Ratio, and control of distortions, aberrations (e.g. spherical aberration) and colour reproduction?

Thomas: At ZEISS we have measurement equipment for all kinds of performance criteria and individual aberrations. For example, wave-front analysis gives you a deep insight into aberrations like coma, astigmatism and spherical aberration. The big difference to cinematographic lenses is the image evaluation with the eye. You do not have a fixed plane sensor with a certain spatial resolution but a very individual acquisition device like the human eye. A lot of experience is necessary to take this into account.

Troubador: How do you co-operate with Purchasing and Production personnel to meet cost targets?

Thomas: Please see my earlier answer, regular communication is necessary and therefore both are directly involved in the R&D project team for a new product.

Troubador: Please outline the information you were given to begin developing the SF32 optical system and how this led to the concept for the system. How was this concept developed to meet the target specifications, and how difficult was this?

Thomas: Two of the main driving targets for the new SF32 are the enormous FOV and the Ergo Balance concept meaning you have to shift the centre of gravity closer to the user. And of course, everything without sacrificing any optical performance because the product is in the Victory Line. The objective has to be lightweight albeit having this large field angles coming into the binocular. Large field-angles generate large aberrations that need to be corrected very effectively. This is very challenging. From an optical point of view, certain aberrations have to be corrected in specific parts of the complete system. It is impossible to arbitrarily shift the aberration contributions.

Troubador: SF 8x32 not only has a significantly larger FOV than SF 8x42, its eye relief is an increase from 18mm to 19mm. Was this difficult to achieve? Tell us more about this.

Thomas: Yes, both criteria make life more difficult for the optical designer. For the user of the binocular the huge FOV makes orientation much easier and the longer eye relief also helps to feel comfortable even with glasses during observation. But higher refractive powers are necessary within the optical system and therefore aberration contributions increase. You have to find a smart lens configuration to achieve both.

Troubador: Please describe the distortion profile of SF32 starting from the centre of the FOV.

Thomas: Distortion is one of the topics where the difference between designing a lens for cinematographic applications and visual instruments becomes very obvious. For cinema lenses distortion is an aberration that is corrected to almost zero right to the edge of the FOV. But visual perception is conditioned to expect a certain gradient of distortion over FOV. The SF32 is designed to match this gradient very precisely to have a comfortable viewing experience for the user.

Troubador: Why a doublet focuser? Was this simply to move weight a little further away from the objective end of the binocular?

Thomas: The objective is designed to be very lightweight to shift the centre of gravity closer to the user. Making the focussing lens a doublet is a smart choice to achieve stable colour correction.

Troubador: The ‘cage’ housing the focusing doublet seems large and elaborate. Is the circular element nearest the prisms actually an anti-glare baffle, that moves with the focuser, and has this proved more effective than other anti-glare measures? If not, what is the purpose of ‘cage’ and the circular element?

Thomas: Actually, we put a lot of effort into reducing unwanted stray light for the SF32. As mentioned previously the big ray angles cause more stray light. Advanced optical simulations are necessary to find all unwanted ray paths through the system and stop this light e.g. by putting mechanical stops at the right positions. We optimized the complete system optics and mechanics to reduce parasitic light to the minimum.

Troubador: It appears that the extra lenses have reduced the transmission slightly compared with SF42 and that High Transmission glass has only been used for the prisms. Why wasn’t HT glass used for more elements?

Thomas: High transmission optical glass is most effective in thick lenses or long prism-paths. The high transmission is referred to the internal transmission of the glass block. But total transmission is also influenced by coating technology of the glass-air-interfaces. And glass selection for the individual lenses is not only driven by transmission, but also by colour- and aberration correction. So you have to find a good balance between competing demands.

Troubador: We can see from published images that the optical system is very different from SF42, why?

Thomas: Three essential quantities are very different comparing these two products: the entrance pupil, the FOV and the close focusing distance. All three of them influence the development of the optical design a lot. To find the best solution and shift the centre of gravity close to the eye position a new design form had to be developed to exactly fulfil these demands for SF32. There is no global best design. We always try to find a specific and optimal solution for the goals that are important.

Troubador: Finally, it has been suggested that binoculars are only made to be ‘just good enough’. What is your opinion of this and also the star test used by some enthusiasts to discover the presence and extent of the aberrations present?

Thomas: First, resolution on and off-axis is only one criteria when designing binos. For example weight/size and the desired total transmission (not to mention cost….) limit the number of lenses, and therefore the degrees of freedom to use “aberration correctors” significantly. So you have to balance different and often contradictory needs of the user and find the best solution for the user within the given constraints. I would be very happy to design a bino with no aberrations at all …..but this would end up in a horrible size, weight and cost.
And second, the evolution of the human eye is much slower than the e.g. the evolution of CCD sensors. For cine or photography smaller pixels demand for higher optical resolution. The pixel pitch of the human eye has been quite constant over the last centuries…😉. And additionally, the subjective visual perception is very different for different users looking through the same bino.
As for the star test, for me as an optical designer, the comparison between good and bad aberration correction is only possible with objective measurements equipment like interferometer or MTF that produce numbers.

Troubador: Thank you, Thomas, for what has been a fascinating glimpse into the role of an optics engineer.

Thanks Lee for most things covered and the open discussion by Herr Steinich.

I have seen remarkably good Schneider T.V. lenses of old and have been surprised at the very high quality of several old Zeiss 75cm Telikon lenses used on Zeiss survey cameras.

Also the Zeiss 50mm f/0.7 lenses for Hassleblad and Apollo missions.

The 1920 Zeiss photo Aero triplet 120cm f/7 was also impressive.
It is still being used.

Hello Lee,

Thanks for the interesting interview and thanks to Herr Steinich for giving such informative details.

Stay safe,
Arthur :hi:
For cinema lenses distortion is an aberration that is corrected to almost zero right to the edge of the FOV. But visual perception is conditioned to expect a certain gradient of distortion over FOV. The SF32 is designed to match this gradient very precisely to have a comfortable viewing experience for the user.
Among the questions that actually were answered, ;) this is even more elliptical than usual. What distortion is he talking about here, pincushion or... ?, and what "gradient" of it are we conditioned to expect?

And additionally, the subjective visual perception is very different for different users looking through the same bino.
So we can't talk about it? What then are the objective goal "numbers" based on?

I have to say, I wish someone would build that no-compromise binocular of "horrible size weight and cost", virtually aberration-free, just so one could see what the difference would be, if perceptible at all. (Was the WX it, and should I try to find one?)
I wonder whether we could custom order a color profile eg. warm, green, yellow etc like each of us wants?

Among the questions that actually were answered, ;) this is even more elliptical than usual. What distortion is he talking about here, pincushion or... ?, and what "gradient" of it are we conditioned to expect?

i think he is talking about the distortions present in the human eye and with which the eye and brain are comfortable, and how binos can be made to be compatible with these.

This long interview was in preparation for some months because Herr Steinich is so busy being involved on many projects, and there came a time when I felt it needed to get published, warts and all.

Cinema lenses usually give the same image as the camera pans across the scene.

There is an interesting Arri YouTube video given by an Arri lens expert on their £20,000 Prime lenses.
It goes into detail and how the lenses have certain corrections going from macro to normal distance.
It mentions that some of the glass costs more than gold.

From memory the Zeiss cinema lenses were generally more affordable than say Arri, Cooke, Leica or the Japanese makes, maybe Fujinon and others.
Some of the Zeiss lenses may be made in Japan.
Cooke has now reintroduced the Speed Panchros from the 1950s, so much is the demand for classic cinema lenses.

Thanks for this interesting read. I like the personal style of your questions and the "non-marketing-bla-bla" straightforward speech. Good to see people like him work in the industry.
Thanks for this interesting read. I like the personal style of your questions and the "non-marketing-bla-bla" straightforward speech. Good to see people like him work in the industry.

You are welcome.

And thank you to Petra for facilitating this interview.

Hello Lee,

Thank you very much for the interview. Soon, Zeiss is going to announce their exit from the hunting optics market (i.e. no more Zeiss riflescopes) This will give Herr Steinich ample time to balance the weight distribution in all Zeiss binoculars and spotting scopes.

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