by Hayden B. Baldwin
|Image distortion occurs when taking a photograph
without a "normal" lens. The switch from film to digital has created
a problem with DX, APS-C and full frame imagery (FX). In years gone
by we photographed the indoor scenes with 28mm (wide angel) lens and
for outdoor scenes and shoeprints we used 50mm (normal) lens. That
was the standard. Now that we have DX size sensors and zoom lenses
that many police agencies use some are experiencing difficulty in
understanding some simple concepts. Just putting a scale in an image
does not mean the image is factual at 1:1. I have seen
many CSI's using a zoom lens to capture images for comparison taken
at the wide angle setting. This causes distortion of the image
that may create problems in comparison and later in court.
Here is an example of this. The following animated GIF is two
images being flipped back and forth. One is taken with a Nikon D300
(DX) 18-70 zoom lens setting at 18mm and the other at 35mm. 18mm on
a DX sensor is equivalent to a 28 mm on a 35mm camera and the 35mm
setting is equivalent to a 52mm on a 35mm camera (full frame).
So when photographing an object to show proper size please use a "normal" lens setting for your particular camera rather than a wide angle setting.