Quote Originally Posted by Ken.Cartouche View Post
You know, it's funny that you mention the difference between those two Nikkor lenses. I had gone to my copy of The Nikon Manual earlier in the day to reference the specs page on the F-mount Nikkor-H 50/f2, and I noticed that it was a double Gauss design, and not a Sonnar like I had understood the rangefinder version to be. That double Gauss design is a Planar, is that right?

I had known that the I-22 was a Tessar f3.5 clone, and I had known that the I-50 was an improved I-22 (though I'm still not clear on how it was improved), but I did not know that the I-61 was a Tessar f2.8. I've read that f2.8 is about the limit of the Tessar design, and that it's really better suited as a f3.5; does the lanthanum glass make an improvement on that?

And, did Zeiss ever make a Tessar in LTM?
Actually the Planar (a trade name) is a dG. The dG can be traced back to a telescope objective designed by K.F. Gauss. The lanthanum glass Tessars can be very very good - another example is the f:3.5 version on the Rollei Ts, I had one that was really superb. But f:2.8 is asking a good deal of the Tessar design, regardless of the glass used. I prefer the F;6.3 Tessars for large format (such as the Commercial Ektars).
The only Zeiss lenses (AFAIK) made in LTM were made during the war, they made the 50mm Sonnar(s) in a very small series.