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New trend of standard lens design?
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PostPosted: Wed Sep 16, 2015 4:21 pm    Post subject: New trend of standard lens design? Reply with quote
Zeiss announced a few days ago the release of a new series of manual focus lenses, the Milvus series, which includes 21/2.8, 35/2, 50/2, 50/1.4, 85/1.4 and 100/2. I notice that the 50mm f1.4 is a Distagon, which is similar to the Otus 55mm f1.4 in name. Would that be a new trend to design a high end standard lens by using inverted telephoto design? What could be the possible reason for that? What's wrong with symmetrical design like Planar? Any idea?


PostPosted: Wed Sep 16, 2015 4:34 pm    Post subject: Reply with quote
We had a discussion about this when the Otus was released.

In short, the distagon type allows for more highly corrected lenses.

However, the double gauss Planar type is far from dead, one place you will find it still in use in in high end projection lenses.


PostPosted: Wed Sep 16, 2015 7:35 pm    Post subject: Re: New trend of standard lens design? Reply with quote
cambug wrote:
Zeiss announced a few days ago the release of a new series of manual focus lenses, the Milvus series, which includes 21/2.8, 35/2, 50/2, 50/1.4, 85/1.4 and 100/2. I notice that the 50mm f1.4 is a Distagon, which is similar to the Otus 55mm f1.4 in name. Would that be a new trend to design a high end standard lens by using inverted telephoto design?

Definately yes.

cambug wrote:

What could be the possible reason for that? What's wrong with symmetrical design like Planar? Any idea?


The Planar, which was developed in the 1890ies, has some difficulties as a "normal" lens on (D)SLRs. Basically being a symmetrical lens, the aperture should be in a distance of about 50mm from the focal plane, if a focal length of 50mm is desired. Since the mirror requires 35-40mm space, a corresponding symmetrical Planar would be of quite limited size and thus, performance.

This is the very reason why high performance Planars from the 1960ties had an effective focal length of about 60mm (the famous Minolta MC 1.2/58mm in reality is a 59.5mm lens).

The "classical" 50mm Planars from the 1970ties and 1980ties are already quite asymmetrical designs: The diameter of the entrance pupil is not the same as the diameter of the exit pupil.

The idea of using a Distagon is, basically, to have basic lens with a larger focal lengths (e. g. a Planar of 60 or 70mm), and then to reduce its focal lengths by using a negative "wide angle converter" in front of the basic lens. A very nice example for this principle is the Minolta AF 1.4/35mm.

Stephan


PostPosted: Thu Sep 17, 2015 6:09 am    Post subject: Reply with quote
A real symmetrical setup would be at magnification 1 and full symmetrical lens - a relaxed design.
To design a lens for normal photographic use at much larger objects than sensor / film size is first non symmetric thing - this gives some tension on the optical design.
For (D)SLR use the mirror needs some room. For this you build up further tension on your "symmetric" design.
The more and more tension you need, the more difficult it gets.
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