Originally Posted by
Pere Casals
I've a Sironar-N 300 MC, the APO Sironar-N 300 is mostly the same, not exactly.
I've never seen a Sironar-S...
In theory ED glass (in the S) helps eliminate secondary chromatic aberration (green-magenta color fringes), so (also in theory) the S should deliver slightly better "microcontrast" in fine textures after a high enlargement, but this would not (IMHO) improve general contrast, because modern multicoatings are the perfection.
ED glass has a lower index of refraction so elements are more curved for the same focal length, and I guess this is related to the weight increase in the S version.
My guess is that if we can notice a difference (in some conditions) it would be more related to microcontrast that to the general contrast.
The S is optimized from 1:10 magnification to infinite, while the N is optimized from 1:20 to infinite. The S is made with some ED glass while the N not. The S has an slightly larger circle. The N may be slightly sharper in the 4x5 corner (see MTF graphs from Rodenstock), while the S may be sharper if going farther than that.
Both the N and the S can generate flare, not because the lens itself but because the very large circle may illuminate (and reflecting in) the bellows more than the film sheet, so a perfect job requires a front hub to trim the 425/450 too large circle to the required 8x10 size.
IMHO a sound 810 shot depends more on the photographer than in if the glass is S or N. Avoiding vibrations (wind), camera alignment, film flatness, using right aperture vs DOF, etc may be way more critical.
Of course the S is a better lens, but I guess that it can be really difficult to notice it, for example if using TMY (instead TMX) you have a sharpness limitation from film that won't allow to see difference in the negative.
I'd say the S is not more contrasty than the N, IMHO any lack of contrast may be related to reflections inside the bellows because the huge circles.
What's about sharpness, even if placing the nose on a 2m print I guess we would not see the limits of an N 300.
My N 300 came with some fungus, but this was solved with no performance loss, I guess. I don't know how a lens can be better, in a way that I think that the glass is better than me.
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