SHOOTING TROUBLESOME ART, part II: Shiny Paintings

note: this is a posting for people in the art reproduction business as well as patrons. It is not our intention to be critical of others in the art copy business. but rather to maintain a dialogue on the evolving technology of digital fine-art reprodcution. If you are an artist and have any questions regarding lighting of art for copy, write info@penguindigitalarts.com

We have had artists from time to time who present us with someone else's work with which they are unhappy. Sometimes, their complaints are very subjective and have to do with the limitations of the process (i.e. the brightness of whites when there is no white ink presently available). But as often as not, the problem is the lighting of the original scan, and of these, many concern a painting that is highly varnished. The problem is really not the lighting, but the use of a lens focal length that exacerbates the problem, i.e. a lens that is too "wide-angle" for the task at hand.

Many art-copy places use vertical copy stands that, of necessity require the use of wide-angle lenses, sometimes modified photographic enlarger lenses (because of their flat-field correction). Most of these places have learned adequate work-arounds for the problems of lens flares from glossy works, usually by using a system of dual polarizing filters, one on the camra lens, and the other on the light source. This "cross polarization" is fairly (but not completely) effective in reducing the flare (and specular) problem, but the use of these dense filters also reduces the light to the scanner by almost 90%. This huge light loss is not good for a variety of reasons I won't go into, but the polarizing process also can produce a off-looking painting, devoid of any texture. One artist referred to it as "color forms" printing.

LEN FOCAL LENGTHS

A so-called "Normal" lens refers to a lens with same angle of view and perspective as seen by your eyes. The more technical definition, a lens who’s focal length equals the diagonal of the image plane. This varies from format to format. For a 35mm film camera, it's a range from about 45-60mm. For a 4" by 5" copy camera, its around 135-200mm. Any lens shorter than normal is referred to as "wide angle", any lens longer is referred to as "telephoto". For our copy work, we use a telephoto lens, specifically an APO Ronar 360mm lens.
To really address this "flare" problem, we need to consider a basic concept in physics: that is the angle of incidence (the light source) equals the angle of reflection (off the painting) so that it can be seen by the camera. Logically (and in fact), the farther away the camera is from the artwork, the less it will see the reflection of the lights. The following demonstration shows the relationship between lens focal length and lens flare. I'm using one of our regular patron's "worst-case" acrylics, 40" x 24" heavily varnished. I'm using one of our KODAK PRO SLRs with full-35mm sensor and a couple of strobes in Chimera soft boxes at 45 degrees from the lens axis.The lenses are all Nikon primes, with their approximate 4/5 copy camera equivalent noted. No polarization was used.
The shot at the left was taken at a distance of about 3' with a Nikkor 17mm lens, 4/5 equivelent of about 50mm. This is wider than would ever be used for copy work, but shows the problem at its extreme. The peice "floating" in the center is enlarged from the side.
The shot at the left was taken at a distance of about 4' with a Nikkor 24mm lens, 4/5 equivelent of about 72mm. This is wider than I've seen used in copy work..This mess is a mixture of flare (scattered light) and specular reflections (coherent light).
The shot at the left was taken from about 5' with a Nikkor 35mm lens, 4/5 equivelent of about 90mm. This is lens is commonly used in copy stand work, and has serious specular problems plus some flare.
The shot at the left was taken from about 7' with a "normal:" Nikkor 55mm lens, the 4/5 equivelent of about 150mm. There are still substantial problems.
The platform is just a piece of three-quarter plywood framed out with straight two-by-fours
The easel wall is 8' high and 11' wide made in three sections of quarter inch luan and 2 x 2. It is made straight and plumb by a combination of straight cleats top and bottom, and stage jacks in the back that are micro-shimmed with a level as we go. The whole thing is put together with a lot of sheet rock screws.
We add "meat" to the back of the easel wall as we need to for sheet rock screws to hang canvas stretchers.
The shot at the left was taken from a distance of about 15' with a Nikkor 135mm lens, 4/5 equivelent of about 360mm, coincidentally the focal lenght we use for all of our copy work.
The bottom straight "cleat" also doubles as a shelf when we've had to shoot upper and lower sections, in addition to left and right.
It is noted that this last 2 shots were taken from a distance that is inconvenient or impractical for a vertical copy stand (without a two-story workspace). There are a number of other problems of using wide-angle lenses in copy work, including maintaining good linearity, uniform light transmission across the entire field, and uniform focus across the entire field. These problems are all avoided here at Penguin Digital Arts by using a horizontal copy system, an approach that also makes possible the efficient shooting of large works of art in overlapping sections, as explained in previous pages.
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SHOOTING TROUBLESOME ART, PART I

SHOOTING TROUBLESOME ART, PART III