Sonnar2 said:
You mean Ernostars? :angel:
Yes, Bertele went from the Triplet to the Ernostar to the Sonnar in his development of the lens. But my guess is that he also had access to the Ultrastigmat, which is the closest match to the Sonnar - minus the middle element of the cemented triplet & without the strong cemented rear element.
Every element in a optical group has a reason why it's there in terms of optical correction. An glas-to-glas surface hasn'tr the same refraction as glas-to-air, no to speak about different glas types here. You cannot leave it away just because better coating is available. Of course the main design idea of "not more than three optical groups" was due to the fact that coating wasn't good enough, or even existing, in the 1930's. I haven't to repeat here what I described in my website about 1930's fast speed lenses. But given the fact that the three-optical-groups Sonnar of the 1930's and 1950's shows less flare than concurrent (and even a lot of modern) design, you cannot conclude that the C-Sonnar, having 4 optical groups, has the same or even better flare behaviour. There are millions of 4-optical groups designs showing bad flare. Of course you can believe the marketing statements of Zeiss. But I keep waiting for the prove picture-by-picture, or do it myself. Currently I'm waiting for a Zeiss lens to test.
All of what you say here is true. I'm sure that the missing middle element did serve a design function in correcting aberrations. However, the point is that Bertele really had no other choice without coatings to accomplish this. A lens of that speed would just have been too flare prone with so many glass-air surfaces. Today lens designers do have a choice with a combination of coatings & many more glass types - none of which existed in the early '30s.
I don't know what the behavior of this lens will be, but the design remains asymmetrical, which means that it will certainly behave differently than the double-Gauss designs of either the pre-ASPH Summilux or the current ASPH. If this is the look that a photographer wants, this means that he will have another choice. (The current ASPH Summilux is of course a very advanced design, not only using aspherical elements but also a floating element. Although it is at its core a symmetrical design, it is an oversimplification on my part to refer to it as just that. Still, a different design & a different fingerprint.)
As Leica works toward increasing sharpness with each new generation of lenses, they abandon the old designs. The interesting aspect of the Zeiss decision to offer the ZM lenses is that they are proposing that there is still a market for the old designs.
Why not, if I don't have the lenses yet? Sharpness isn't that much. That's what MTF charts are for, correct?
Regarding MTF, I wasn't challenging or criticizing. Just asking. No problem.
I would note that there are limits to what conclusions can be drawn when comparing MTF results from two different companies since they are derived differently by every manufacturer. Zeiss publishes measured results. One of the first things they did at Cosina was to install their own MTF plotters. Leica's results, on the other hand, are calculated. So, it's fair to say that the Leica results are an ideal that they strive for & not necessarily what one will get in real world use. Zeiss MTF data should be much closer to the real thing with only sample variations accounting for differences.
Even given the differences between the two companies, I have a hard time seeing any significant difference between the Sonnar & the pre-ASPH Summilux - ignoring of course the Leica data for 5 lp/mm. (I have no idea why they publish this.) What I see is that each of the curves is different at 10, 20, & 40 from that of the other lens at the same lp/mm. You could conclude that one lens is better than the other depending on what point on the curve you are comparing. They just seem to have different signatures. Comparison is further complicated by the fact that Zeiss publishes these curves at f/1.5 and f/4 while the ones I have available for the pre-ASPH Summilux are at f/1.4 & f/5.6.
While some conclusions can be drawn from these MTF charts, they are largely published for marketing purposes. In their own manufacturing & design process, lens designers are looking not at one, two, or three MTF charts, but at data at every aperture & every shutter speed. As close as these two lenses are, you'd probably need that amount of data to define the differences between the two.
Judging by the MTF charts, I would agree that the ASPH Summilux is the sharpest lens of the three - especially at f/1.4. At 3 times the price, I would hope that it offers something other than the Leica name. As I said earlier, I see it as a positive that Zeiss is offering these old designs to those who are interested - even if the lens is not the sharpest knife in the drawer & even if the modern design is not an exact replica of the original design. Being able to choose a different "look" is a good thing I would think.
