Image circle confusion / Graflock backsgreenspun.com : LUSENET : Large format photography : One Thread
2 unrelated beginner's questions: 1.) Is "International Standard" back the same as "Graflock" style? If not, what are the advantages/disadvantages of each? 2.) 4x5 format requires an image circle of at least 161 mm. The Rodenstock Grandagon 35mm and 45mm lenses have an image circle of 125 and 131mm respectively, yet are advertized as covering 4x5 format in the B&H Source book. How does this work? Am I missing something??? I apologize for my ignorance...
-- Andreas Carl (firstname.lastname@example.org), July 11, 1999
1: Yes they are the same. Since Graflock was a trademark others like Linhof had to use a different name.
2: You are not quoting a reference source. You are quoting a sales catalog. We as the Rodenstock distributor supply factory spec sheets. Those are reference sources. If you would like the ones for Rodenstock lenses we need an address to mail them to in the US.
The circles quoted for Rodenstock 35 and 45mm lenses are, by the way, at f11 for the 35mm and f16 for the 45 (and 55). Not at f22 as with their other lenses. This is because the specs are given at the smallest aperture without diffraction.
Rodenstock specs the 35 and 45mm lenses as covering 6x12cm. That would mean that they will not fully illuminate the corners of 45 and, of course, not allow for direct displacements. However many architechture and landscape photographers have been using these lenses very successfully on 4x5 and View Camera will have a review of the 35mm by Norman McGrath in the next or the following issue. He, of course, uses it on 45 for architechture.
-- Bob Salomon (email@example.com), July 11, 1999.
Thanks Bob for clarifying this. If I understand you correctly, "image circle" is not an absolute, but a gradual tapering-off in light levels, so even if the 35mm and 45mm lenses have an image circle less than what's required for the 4x5 format, the light fall-off would still be acceptable for most applications, especially when using the center filters? I am looking forward to Norman McGrath's review. Thanks!
-- Andreas Carl (firstname.lastname@example.org), July 11, 1999.
Andreas, FWIW the diagonal of the actual IMAGE area of a 4x5 is closer to 150 or 151 mm; 160 or 161 is the diagonal of the piece of film, including those black borders (the precise measurement depends on your holders; my Readyloads are 151). That centimeter can make a difference when calculating movement possibilities....
-- Simon (email@example.com), July 11, 1999.
Andreas, you'll have to crop the 4x5" if you use lenses with such small image circles that are "meant" for 6x12 cm as Bob points out.
-- Carlos Co (firstname.lastname@example.org), July 12, 1999.
When focused closer than infinity, the image circle gets larger, and since most shots are taken at some hyperfocal setting, so you would have more coverage than the numbers would indicate.
-- Ron Shaw (email@example.com), July 12, 1999.