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Matinee: Hubert Nasse Talks Lens Design
4 October 2014
Saturday matinees long ago let us escape from the ordinary world to the island of the Swiss Family Robinson or the mutinous decks of the Bounty. Why not, we thought, escape the usual fare here with Saturday matinees of our favorite photography films?
So we're pleased to present the fifty-third in our series of Saturday matinees today: Lens Design 101: Interview with a Zeiss Master.
In this recent 37-minute interview with Dr. Hubert Nasse, photographer Matt Granger covers a lot of ground with the senior scientist for the Carl Zeiss Camera Lens Division. You do get the feeling by the end of the interview that there will be test.
With a background in physics, Nasse spent the first 15 years of his 30-year career at Zeiss in the microscope division. He's not a designer, he says, but just a quality assurance guy who brought along his microscope to "check the output."
He happens to now a little about lens design, though. And he shares what he knows in plain English with Granger.
Here's just a few of the topics they discuss:
- Why 50mm primes are the most compact.
- Why camera mirrors complicate lens design.
- Some zoom focal length ranges (often in the middle of the zoom's range) are sharper than primes.
- Computer design isn't the only reason new lenses outperform old ones, but it's the top three reasons.
- How we make glass these days is different than how it used to be made (with lead and sand). We've had to lose the lead.
- An explanation of abnormal partial dispersion.
- The front element of some lenses (like the Otus 85mm they pass back and forth) is concave rather than convex.
- The only impediment to lenses designed without compromise is physics. Which is why the Otus lenses are large.
- Reflection from the sensor is a big issue in lens design. Sensor reflection is 10x the problem it is in the lens itself. So coatings alone can't compensate and the shape of the lens has to be modified.
- Each surface of a lens element interacts with all the others.
- Why no modern lens foregoes multicoating. It makes multi-element zoom lenses possible, in fact.
- How twin-lens reflex lenses differ.
- Why Nasse loves the 85mm focal length for practical use (it's perfect for people photography, he says) but still has a fondness for the Zeiss Biogon.
- He explains why faster lenses can't color correct for their high speed.
It's fascinating stuff from the horse's mouth. It's a video but there's not a lot to see (the angle of view changes only about 16 minutes in when they seem to get a second camera set up). So feel free to close your eyes and pretend it's an audio podcast.