Image Circle of Rodenstock Apo Sironar N 360

[Richard K.]

Just curious why the image circle of the Rodenstock Apo Sironar 360 N specs out to just 435 mm compared to over 494 for the Nikkor, 491 for the Apo Symmar and 485 for the Fujinon. Since these are all plasmats in Copal 3 shutters (maybe this is my problem! maybe they're not?), what has Rodenstock done (or not done) to produce this result? I suspect vignetting from the rear barrel? Then why not flare it? This seems a bit anomolous. Interestingly the image circle is 425 for its 300mm focal length and 500 for its 480mm focal length, more as expected and in line with the progression other manufacturers exhibit. So, who can please explain what happened at 360?

[Richard K.]

Hmmm...maybe I should rephrase this. Why of all the 360 mm focal length plasmats with typical image circles of around 490mm does the Rodenstock Sironar 360 have only a 435 mm image circle?

[Oren Grad]

I've wondered about that myself. Even the 360 Apo-Sironar-S comes up short, at least by specification.

So...

[Richard K.]

Anybody?

[Bob Salomon]

Rodenstock is conservative. And the 360n covered 64° and all of the shorter N series are 72° coverage lenses. The 480mm covered 56° and the 360mm S covers 68°.