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09-26-2014, 10:02 PM - 3 Likes   #1
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Lens Design 101: Interview with a Zeiss Master

36 min recent interview with Dr Hubert Nasse, who has worked at Zeiss for 30 years. Interesting insights into some of the design considerations in lenses.



Dan.

09-26-2014, 11:36 PM   #2
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Very nice! Thanks!
09-27-2014, 01:13 AM   #3
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Thanks for posting. For a geek like me thats pretty interesting.

The part lens coatings play on transmission, I did not realise... I thought a poor coating could reduce transmission but it did not occur to me that a coating could actually improve transmission (perhaps due to less reflection?).
09-27-2014, 01:48 AM   #4
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QuoteOriginally posted by kiwi_jono Quote
but it did not occur to me that a coating could actually improve transmission (perhaps due to less reflection?).
That's the main purpose of lens coatings. Each lens-air or lens-lens transition in the lens incurs a little transmission loss, both through absorption & unwanted dispersion/reflection. With say 15 elements in a zoom lens, that's 16 transitions. Without coatings, both internal & external, the losses would be significant. Of equal importance is the effect of the dispersions on contrast. I have an old cheap lens with little/no lens coating, and I always have to boost the contrast in PP. However there's no way that a simple global PP contrast boost can reverse the image muddling created by all those aberrant reflections/dispersions ("ghosting") bouncing around inside the lens.

I suspect this ghosting, and the related veiling lens glare in high contrast situations (e.g. the area of unwanted glare around street light shots), are significant contributors to perceived image quality loss. The reduction of reflections/ghosting may be an important component of the "pixie dust" that separates the great lenses from the good ones.

http://www.imatest.com/support/image-quality/veiling-glare/
http://www.imatest.com/docs/veilingglare/

Since primes usually have less elements, I suspect this is one of the reasons they generally look better than zooms.

Another purpose of coatings is protection. Hence Pentax's SP coating is claimed to make it easier to clean the external surface of the front element. (I presume it's on the outside of the exit element, as well.)

Note Dr Nasse's mention of the unsophisticated coating on top of the DSLR sensor, creating some reflection from the top of the sensor (typically the IR filter coating) back to the lens.

Dan.


Last edited by dosdan; 09-27-2014 at 03:10 AM.
09-27-2014, 02:55 AM   #5
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QuoteOriginally posted by kiwi_jono Quote
Thanks for posting. For a geek like me thats pretty interesting.

The part lens coatings play on transmission, I did not realise... I thought a poor coating could reduce transmission but it did not occur to me that a coating could actually improve transmission (perhaps due to less reflection?).
The coating not only improves the transmission of light energy.
In the modern times it plays significant role in the hole optical properties of the lens!
09-29-2014, 01:00 PM   #6
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An interesting comment on ghosting from a lens designer:

Re: Relationship between microcontrast and flare?: Photographic Science and Technology Forum: Digital Photography Review

Dan.
09-29-2014, 03:00 PM   #7
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I enjoyed watching this clip. Dr. Nasse was generally able to communicate complex ideas in clear and simple terms. Sometimes his word choice wasn't perfect, like when he was talking about different wavelengths of light taking different paths. I think that was more of an English/German internal translation challenge for him. The interviewer wasn't completely professional. Too much interjection.

Seriously though, excellent clip!
10-30-2014, 01:55 AM   #8
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Im normally not very interested in the technical part of photography (knowing to much often distracts me more than helping me), but this interview got my attention. It was very relaxed and spoken in words i can understand. I often wondered why there is so much glas used in some optics when it is said that every layer of glas hurts the final image, but now i get a better idea.
I like these kind of easy to listen technical interviews. Perhaps Matt was a bit to rash sometimes, but they are usually on a tight schedule at such a big event.

11-04-2014, 04:46 PM   #9
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Its a bit long. I'll just post in this thread to subscribe to the thread, will watch later.
I would be more interested if the interview were with the designers of the FA limiteds
11-05-2014, 04:39 PM   #10
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in fact, over the past 100 years, the production of optics not much has gone forward, the scheme is almost the same (with modifications of course) but cardinally new no one has yet invented.
I know photographers who shoot on medium format camera 50-60 years of birth. And they have been exhibited in galleries, know their names. but the technique is old !!
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