Absorption in Photography and Digital Imaging

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by Chuck Groot www.ChuckGroot.com www.SuccessfulPhotography.com

Absorption means the taking up of one thing by another; photographers employ the concept in both the chemical and the optical sense.

Certain chemicals like Calcium chloride and magnesium perchlorate absorb and retain atmospheric moisture. The sensitive emulsions of plates and films can absorb small amounts of dyestuffs that allow us to colour them as in the old-fashioned way of hand colouring. Hint - save those little packages that come with medications and other items that are used to absorb moisture, because they have the above-mentioned chemicals in them and these packets can be put in your camera cases and with your batteries to keep them from being ruined by moisture.

However, the term "absorption" is most often used in an optical sense. Partial or total elimination of light rays can occur when they pass through a medium. For example, when we put a red filter on our background flash, it will absorb all of the other colours except the red ones. I often use a variety of plastic report covers and cut small patterns in them and place them on my background flash to create a variety of unique effects. This method is a very inexpensive and fast way to change the look of an image.

On the other hand, an article, which absorbs all of the light rays that fall upon it, appears black, since it reflects no light at all. This is a very important principal to understand. So often I have been asked by photographers why they have colour shifts, colour casts, or colour cross-overs in their pictures? I tell them that 90% of the time the reason is that their darkroom, studio space, computer room, or display area have heavy colour saturation which competes with the colours in their images.

For example, if you are working in your computer room and it has a slight pink tone to the walls and you print an image or have your lab print your image, often you will be disappointed with it. Chances are that you were correcting for the pink cast being reflected on your screen and the resulting hue your print will show will be a bit greenish. Likewise, if your studio has blue walls, these will be reflected on your subject and the lab will automatically try to correct for the cast, but you will get a cross over-effect and end up with greenish prints. It is amazing how sensitive computer screens are.

The best way to combat this problem is to have the walls in your darkroom, computer room, and studio painted 18% grey. This way you will have no colour casts on your images and low reflection to affect your light readings. This may seem over the top, but with today's highly sensitive films and digital cameras, reducing the amount of variables is the best way to go.

? Chuck Groot writer, teacher, lecturer, photographer, consultant. Email chuckgroot@shaw.ca www.chuckgroot.com, www.successfulphotography.com

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