Originally Posted by
rdenney
It is difficult to compare short focal lengths between different shapes and sizes of formats. You can divide the focal length by the horizontal dimension of the format, or by the diagonal of the format, and that gives you a factor that can be applied to other formats. But that only gives you an idea.
But, to do some math, a 21mm lens in 24x36 format is just about half the diagonal of that format. A 75mm lens gives you about half the diagonal in 4x5. For 6x12, it's about 60 or 65mm that gives you half the diagonal. But 6x12 is such a different shape than 4x5 the feel will be different.
I find that a 47 on the 6x12 format will give me an extremely wide sense--perhaps sometime like I would expect with a 17 or 18mm lens on small format. On 6x7, a 47 is a strong wide--sorta like a 24 on small format. With 6x9, a direct comparison is much easier, the 47 is about like a 20.
On 4x5, a 90 feels to me like a 24 does on small format, and a 65 feels like an 18.
If you want the feel of a 20-22mm small-format lens on 4x5, see if you can borrow a 75 to try out.
By the way, if you get a 47 for use with roll-film, you don't need the latest 47XL. The older 47/5.6 non-XL will cover roll-film formats, though it's marginal on 6x12.
Remember that focal length and coverage are different dimensions. The ability to move the camera close to get the exaggerated perspective is a function of focal length only, as long as the lens in question has sufficient coverage for your format.
All modern 75mm large-format lenses have coverage for 4x5, including the Schneider Super Angulon (any of them), Rodenstock Grandagon, Fuji SWD, and Nikkor-SW. If you want to use movements, then the variations in their coverage become more important. Nearly all 65mm wide-coverage designs will also cover 4x5, though some were designed for smaller formats (the old 65/8 Super Angulon is the most marginal of these). Lenses shorter than that are too short for what you describe, in the 4x5 format.
There are many ways to convert between equivalent focal lengths in different formats, but they feel different in different formats, especially considering the different way in which most people approach the different types of cameras. What seems nice-and-wide on 35mm might seems freakishly wide on 4x5, when comparing equivalent focal lengths.
When I want the feel of a 24mm lens on small format, I grab a 45 for 6x7, a 47 for 6x9, a 65 for 6x12, and a 90 for 4x5.
Rick "who likes short lenses" Denney
Bookmarks