non digital lenses on a digital back anyone

[David A. Goldfarb]

It's hard to make a good comparison without lenses of the same focal length and the same subject in the same lighting and the same subject distance and aperture, but here are a few portraits that I have on my website--

The main interesting quality of a Dagor is that it has a very large image circle for a relatively compact lens, but here is a 12" Gold Dot Dagor at around f:14 on 8x10"--



This is a 360mm Heliar probably at f:5.6, which is a little closer to wide open than I usually prefer also on 8x10". The main quality of a Heliar is the sharp line of separation between the in focus and out of focus portion, but this isn't the best example of that, because the DOF is short--



This is a B&L 5x8" Tessar (around 240mm), probably around f:5.6 on 5x7". Tessars tend to be very sharp at the plane of focus, and then show gentle falloff of focus moving away from the point of sharpest focus--

[GPS]

[QUOTE=Oren Grad;222226...
Re the 36x48 sensors that are found in high-end backs, Rodenstock claims that design of their "digital" lenses is optimized to address several issues:

(1) reducing chromatic aberration to less than the pixel dimension
(2) enhacing performance at wider stops (f/8 or f/11) to minimize diffraction losses with the shorter focal lengths needed for small sensor formats
(3) minimizing curvature of field for these rigidly planar sensors

Also, with the HR series in particular, the design is supposed to take into account the properties of the CCD cover glass.
...[/QUOTE]
4) digital lenses are constructed as giving higher resolution (than he rest of LF crowd)too.

[Gene McCluney]

There are two type of digital back suitable for use on Large Format cameras, there are the Bayer-pattern types which use a largish imager chip and capture instantaneous images. The second type are the scanning-backs such as the current Betterlight, these use a full RGB imager that travels across the film plane, in effect scanning the image formed by the lens. Of the two, the Betterlight style is the only one that can take advantage of amost the full image area of a 4x5 camera, and these also seem to be insensitive to off-axis lens placement needed for distortion control or depth-of-field corrections. Therefore the Betterlight scanning type is the best choice to use conventional LF lenses not specifically designed for digital. The Bayer-pattern "chip" type backs, are limited to chip sizes smaller than 6x6cm medium format, and are much more sensitive to lens movements, which often produce fringing and color shifts without electronic correction, thus they are more suitable to medium-format camera styles which have a relatively "fixed" lens position in relation to the digital back.