Thursday, June 23, 2011

Copying Artwork - a Polarization tutorial

Photographers are often asked to digitally copy and print the artwork of other artists. Many of you are artists, who reproduce your own artwork, and would like to know the best way of copying your work.

I once ran a business doing digital copy work. Many artist would reluctantly come to me after their own copying efforts fail to accurately reproduce their artwork. Most would lean their paintings up against the wall and take a few shots with their digital camera. Although most 10MP to 12MP point-n-shoot cameras have enough resolution to make a decent 16 x 20 print (or even a 24” x 30"), megapixels are only a small part of the requirements for making a good reproduction of an original painting.

Proper lighting is the most important ingredient in good copy work. In this tutorial I will show you how to set up proper Polarized lighting and achieve a technique called, “cross Polarization”. Here’s one of the most dramatic examples I’ve seen:
Without & with Polarized lighting - painting © Golden MillwardThe image on the left is with regular lighting, and the image on the right is with cross Polarization lighting and filtration (painting by Golden Millward). Click on any image to see a larger view and additional information.

A more typical comparison is this painting by Cindy Christiansen. The Polarized copy on the right has rich colors, a high Dmax, and a full range of tones. Without & with Polarized lighting - painting © Cindy Christiansen This is because cross Polarization eliminates the reflective “haze” associated with regular lighting.

Here’s the set-up you’ll need to do Polarized lighting (click on the image for more information about each piece of equipment in the photo). Polarized lighting set-up: for a vertical copy stand The lights are regular studio strobes ("retired" Normans that are too heavy for location shooting, compared to modern, light-weight strobes). The camera and copy stand are positioned in the middle.

Polarizing filter attached to light reflector with multiclips The key elements are the Polarizing filters attached to the strobe’s reflectors via Manfrotto 375 Multiclips. The clips can be ordered as a pair through Amazon, Adorama, or B&H, and typically cost between about $15 per pair. They hold the filter away from the light so that it is not damaged by heat (and allow air to circulate). The Polarizing filters are Rosco #7300 Polarizing Filters (17” x 20"). They can be ordered through B&H, and cost about $50 each. NOTE: Each filter has an axis mark or arrow that will show you the way the filter must be positioned or rotated in order to achieve proper Polarization. It is this axis, together with the proper rotation of the circular Polarizing filter on the camera lens that cancels or filters out all stray light that causes interfering reflections on your artwork.

Your next most important ingredient is your lens. copy-camera-lens-closeup_2492c It should be a standard focal length (50mm for DSLR’s) macro lens. These lenses are made for close and medium distance work and have minimum distortion (i.e. barrel or pincushion distortion). The circular Polarizing filter attached to the lens is the final piece of the puzzle.

Proper rotation of the circular Polarizing filter will produce maximum cross polarization. Polarization test, using duct tape Here’s a quick test, using duct tape, to determine when you’re at max Polarization (click photo for details).

Finally, place reference strips like the Kodak Gray Scale and Color Patches next to your artwork before copying it. Kodak Gray Scale and Color Control Patches (Q-13) These reference strips should remain through your post-production tweaking to ensure color accuracy and the highest possible tonal range. They can be cropped out just before final printing.

Posted by Royce Bair on 06/23 at 10:55 AM

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