Center Filter Requirements

[Nicholas F. Jones]

Michael's original question concerned Rodenstock and Schneider WA's, which he says require CF's, in comparison with the Nikkors, which he says do not. However, most of the ensuing discussion has concerned only the Nikkors and from it, where my own needs and interests are concerned, I've concluded that I could probably use the 150SW on 8x10 to shoot b&w without worrying too much about fall-off, although I'm still very unclear whether or not this has anything to do with some peculiar design feature of the Nikkor.

But what about Rodenstock and esp. the Schneider super symmar 150XL under similar conditions? Has anyone used the 150XL with b&w on 8x10? As Kerry puts it, the best way to find out if you need a CF is to use the lens without one. Some help here would be valuable, since the B+W 4a CF for this lens is so expensive as to wipe out any price differential vs. the Nikkor 150SW (at this point, I'm uninformed on alternatives to the B+W). Any informed input would be most appreciated. Nick.

[Michael S. Briggs]

Re: "...although I'm still very unclear whether or not this has anything to do with some peculiar design feature of the Nikkor." of the last response. As far as can be determined from the published literature, the non-aspheric very-wide coverage lenses of all four manufacturers use the same optical trick of tilting the pupil to reduce the light falloff. Confusion seems to result because the German manufacturers market center filters and publish data on the illumination falloff, while the Japenese do not. The designs in this class are the Fuji SW, Nikkor-SW, Rodenstock Grandagon (including Apo) and Schneider Super-Angulon (including XL, but not including the plain Angulon). These lenses have falloff going as approximately (cos theta) cubed. While the optical theory says that the illumination goes to the third power, when I analyze the published data, I generally find that the illumination falls off somewhere between the third and fourth power, i.e., a little worse than theory, but still better than a lens that doesn't use the tilting pupil trick. As far as I can tell from the published information, there is no reason based upon illumination falloff to pick one of these lenses over another. Even though the illumination falloff is improved, it still exists and some people for some uses may find a center filter useful for any of these lenses.

The Super-Symmar XL series are super-wide coverage lenses using aspheric technology. From the illumination graphs that Schneider has published, they do NOT use the optical trick to reduce the falloff of illumination. The published curves follow the (cos theta) to the power of four law quite well. Therefore illumination falloff may give a potential buyer a reason to select a different super-wide coverage lens. On the other hand, these lenses are small, light-weight and fast, and these characteristics will be more important for some users. One could always use a center filter with one of these lenses to improve the uniformity of the illumination of the film.

The curves that I just analyzed for this response are those of the 150 mm Super-Symmar XL at <http://www.schneideroptics.com/large/datasheets/ssymxl/ssymxl5,6-150/ssmxl5,6-1 50p1.htm> and the 165 mm Super-Angulon at <http://www.schneideroptics.com/large/super_angulon/daten.html>.