Alan, I think there's something about formats. My most used focal length on 35 mm still is 105 mm, ~ 2.4 x normal. My most used focal length on 2x3 is around 100 mm, normal. And when I was shooting S8 my most used focal length was 6 mm and if I'd had shorter I'd have used it too.
I post links to threads on this forum from other forums all the time.
Yeah Dan, I think you are right. I liked my 25mm and 100mm the best on my 35mm camera. When I bought a Bronica EC 6x6 I shot 40mm, 75mm and 150mm pretty equally. For 4x5 I like my 180mm and for 8x10 I like my 14" the best.Originally Posted by Dan Fromm
Don;
I'll try to steer back on topic and see if I can answer the question succinctly yet thoroughly.
First, it is important to distinguish the angle of view from the angle of coverage. The former is the angle the lens sees, i.e., in front of the lens, the latter describes the angle between lens and film, i.e., how large an image circle is formed by the lens.
The angle of coverage then, has no relationship to whether a lens is "wide," "normal," or "long" for a particular film format. It is the angle of view that does this.
Normal focal length lenses are those in which the focal length is approximately equal to the diagonal of the film format. Therefore, 50mm for 35mm format, 80mm for 6x6cm and 150mm for 4x5 format are all considered "normal" because the angle they see about the same angle as our eyes; ~62°. Wider than that looks progressively wider, narrower progressively longer. This is dependent on angle of view, but completely independent of angle of coverage.
With view-camera lenses, the amount of coverage is important; more coverage is needed than just what it takes to cover the format since camera movements need a lot of extra image circle. Therefore, it is the angle of coverage, often called "covering power" by Nikkor and others, that is the most important and the info that is given in the lens brochures. Schneider confuses things even more by calling the angle of coverage "angle of view" in their on-line info. Often the true angle of view isn't given at all in the data sheets. In any case, the 105° that you refer to for your lens is the "covering power," or the angle of coverage.
There are lenses of the same focal length for 4x5 format that have very different angles of coverage. For example, a 90mm Schneider Angulon has an angle of coverage of 81° and barely covers 4x5 (Schneider calls it "angle of view"...) while your Nikkor 90mm with 105° coverage covers with lots of room to spare allowing you to use rise, shift and front tilts and swings, which would not be possible with the Angulon without causing vignetting.
A common plasmat design 150mm lens on 4x5 throws an angle of coverage of about 70° and an image circle of 210mm; large enough to cover 5x7 and offer a lot of room for movements on 4x5. However, the same lens design with a 70° angle of coverage in 105mm only throws an image circle of 155mm; barely enough to cover 4x5 without movements. If you plan to use camera movements, this isn't the lens for you; you need something in a similar focal length but with a larger angle of coverage/image circle. Fortunately, there are other lens designs that do just that. They are called "wide-angle" in common parlance, which, for LF photographers, means that they have a wider angle of coverage (again, this has nothing to do with the wide-normal-long angle of view of the lens; it relates to coverage). This is confusing to those coming from smaller formats with fixed-lens cameras since "wide-angle" there refers to both coverage and view. We need to keep these two things separate in the LF world, however.
Anyway, we can get a 100mm lens (or in your case a 90mm) with a wider angle of coverage and be able to use movements. The angle of view, however, remains the same and identical photos taken with two lenses of the same focal length will be the same, regardless of the angle of coverage of the lens; the extra coverage just doesn't get used.
You should also know that most lenses come in design families with many focal lengths available in each family. In Nikkor parlance (since you have one) the "W"-series (for wide) indicates a lens-design family (plasmats) with about 70° of coverage (which is wider than simpler Tessar-type lenses, hence the "W"). Schneider calls theirs Symmars, Rodenstock calls theirs Sironar, Fuji is like Nikkor.
There is also a common family of "wide-angle" (of coverage) lenses. Nikkor and Fuji call theirs SW (Super Wide), Schneider Super Angulon, Rodenstock, Grandagon. There are many other design families with varying angles of coverage, but this gives you the general idea. Note that the families overlap. You can get a Nikkor W 135mm lens (slightly wider view than normal) with a 73° angle of coverage and an image circle of 200mm; enough for modest movements on 4x5. However, you can get a (larger, heavier and more expensive) Nikkor SW 120mm lens (close in focal length) with 105° of coverage and a whopping 312mm image circle; enough to cover 8x10 film.
How a lens focal length "feels" on a particular format is part science, part emotion. Angle of view relates directly to the "wide-normal-long" feel of the lens to a great extent. However, as formats get larger, negatives and prints usually get bigger and that feeling changes a bit (especially if the aspect ratio is different); normal angles of view seem a bit "wider" on a larger format for some reason. Still we can get a pretty good comparison by simply dividing focal length by film diagonal. A result of around 1 is "normal" (50mm/50mm=1 for 35mm; 150mm/160mm=0.94 for 4x5). Greater than 1 is "longer" (100mm/50mm=2 for 35mm, 300mm/160mm= 1.85 for 4x5); less than 1 is wider (28mm/50mm=0.56 for 35mm; 75mm/160=0.46 for 4x5). You can extrapolate further easily on your own.
Hope this has helped,
Doremus
Not more-or-less, but based directly on focal length. Angle of View = alpha = 2 arctan(d/2f), where d is typically the length of the film diagonal and f is the focal length of the lens.
Don't confuse angle of view with angle of coverage. Angle of coverage is a lens design parameter. This distinction matters in a world where the film plane and the lens plane are independent as they are in most view cameras (this is what camera movements manipulate). In 35mm where the plane of the film and the plane of the lens are rigidly parallel, these terms tend to get used interchangeably, which confuses the heck out of newbies. At least, it confused the heck out of me.
Bruce Watson
I started to write that lenses would be independent of what is behind them but everybody has a different view of angles, so I stopped.
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