All About Digital UV and IR. Page 7: Which Lenses?

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2024-11-17 02:30:11

Without photographic lenses, we're pretty much lost in our endeavours towards capturing the invisible light (on a tangent note, there always is the possibility of doing pinhole photography). Fortunately, specialised lenses are rarely needed for pictorial UV or IR photography, as you'll learn in the following sections.

Infrared (IR): Virtually any lens can be used for IR photography, provide you can attach the needed black IR filter onto the lens (front or rear). You can employ zoom lenses although I would recommend using fixed focal length lenses because they tend to have smaller filter threads and hence need smaller and less expensive filters. If you apply the inside trick of making an IR-filter by using pieces of black, processed E-6 film, any lens will do.

There will be a degradation of optical quality for most lenses when they are pressed into service for recording IR, but this should not be a critical issue unless you are a real nit-picker (who won't dare to experiment anyway). Likely there will be increased chromatic and spherical aberrations, and a significant shift of focus. Thus, you should always try to stop down the lens because this reduced optical aberrations, and the increased depth-of-field will mask focusing inaccuracy. A rule-of-thumb is to increase lens extension by 10% which is easy to do using bellows for close-ups, but less easy implemented for landscape work. If there is a red IR index on your lens, use it to realign focus before shooting. If the index dot is missing, just focus well in front of the closest subject of interest. For a 28 mm wide-angle lens, a focus setting around 2-5 m will be adequate for distant landscape shooting in IR.