INFRARED
PHOTOGRAPHY WITH DIGITAL CAMERAS
Page
Four
Determining Your Exposure
Depending on which digital camera you're using, its CCDs will be sensitive to different parts of the infrared spectrum and will require different exposures with different filters. The simplest way to check your exposures is to run a test. To do this, set your aperture at a relatively high depth of field and bracket each frame in several stop intervals. Bracketing requires that you take a series of exposures at different shutter speeds.
Since you're not paying for traditional film, I recommend that run a widely spaced bracket.
Bracketing with Different Filters
For this article, I used three filters, two of them were opaque and one red. I began my tests for each filter at the correct of 125/f9.0. Then, I put the filter on and took a frame and set my shutter to 1/60th second, 1/30th second, /15th second, 1/8th second, 1/4 second, l/2 second, 1 second, 2 seconds, 4 seconds, 8 seconds, 15 seconds, and 30 seconds. This was done for each filter, and the times were recorded.
Recording the Exposures
It was relatively easy to determine which of the images had a"normal" exposure ("normal" being a relative term with infrared photography). In many cases, several of the bracketed exposures made for great-looking pictures, so I
reccommend that even if you run a test for each filter, always bracket. I found that exposures longer than four seconds produced "noise" in the image, but even this was pleasing in color.
Various subjects reflect infrared light differently, and you'll find the variations between exposures fascinating. You can simply import the exposed images into any database program like Extensis Portfolio, Canto Cumulus, or in the case below, Nikon’s Capture Software and then you can easily see which exposures and filter combinations are going to work with your camera. The problem you might have is choosing from among the many images you like!
|
Normal Exposure |
125th Second |
f 9.0 |
|
25 Red-ISO 200(two stops) |
1/30th Second |
f 9.0 |
|
188A–ISO 200 seven stops |
1 Second |
f9.0 |
|
87A —ISO 200(nine stops) |
4 Seconds |
F9.0 |
The red visible filters, #25, #29, #70, allow enough visible light to pass through the lens, so you can use your hand-held camera and get spectacular results. In the illustration below, a Tiffen Red #25 was used on a bright day at 250th of a second at f/5.6. The normal exposure without the filter would have been 1000th of a second at f/5.6.
