| IR Photography |
|
|
|
| Written by Guenter Leitenbauer | |
| Sunday, 24 June 2007 | |
|
My gear I use Canon DSLR which is probably the worst gear you can use for infrared (IR) photography. Why? Canon has a very efficient low pass filter in front of the sensor. “Low pass” means that longer wavelengths are filtered out (low wavelengths can pass, long wavelength are blocked). This is necessary, because the sensor (CCD) is much more sensible for IR than for visible light. And IR has a longer wavelength (720nm to 2000nm) than visible light (400nm - 720nm). Other cameras, for example Canon IXUS or Nikon DSLR use a much less efficient low pass filter which sometimes results in a slightly red cast in the black areas of dark photos. Therefore, if you want to concentrate on IR, you need to filter out the visible light. I use Hoya R72 (at 720nm half of the light passes) or Cokin P007 (also 720nm) infrared filters. The problem is: the filter reduces the visible light to a large amount and the low pass filter reduces the rest. So you get extremely long exposure times even in bright sunlight conditions. As mentioned above, for example Nikon DSLR give a lot shorter exposure times here. Another problem results from the highly coated lenses. Some lenses produce so called “hot spots”. This means bright spots in the center of the photo, coming from the coating. For example the Canon EF 1,4/50 has a hot spot, the EF 1,8/50 has nearly none. You can find a list of lenses which are OK for IR photography in the web, just search for “hot spot” and “IR” and “lens”. My equipment, which works quite well:
The conditions and subjects to photograph The most IR light is in the morning and late afternoon. It is not a good idea to try it at midday. There is rather little IR in the light and the bright sun produces a lot of reflexes. The best season is from late spring over summer to early autumn. IR works best, if living green is on the picture. The chlorophyll in the leafs reflects IR extremely good and gives a bright white if you post process it correctly. This effect is called the “wood-effect”. It comes from Mr. Wood who discovered it and has nothing to do with wood. Blue sky and water tends to become very dark, clouds become bright white. So you can achieve dramatic effects here. Therefor the ideal IR subject may consist of clouded skies, water (a river), plants and maybe some architecture all together. Taking the picture Mount the camera on a tripod and define the crop without the attached filter. Focus correctly and then the trouble begin: Focus IR light does diffract less than visible light (in fact, every wavelength diffracts a bit different which results in the so called chromatic aberration). This means: you have to correct the focus a bit or at least use a small aperture (f/11 or so). An example: if the focus on my 50mm lens without the filter is on 10m then I have to correct it for IR to about 8.3m to focus correctly. If you focus without filter then you should always focus to objects that are a bit nearer than the object you want to be in focus. There are tables in the internet for different lenses (it depends only on the focal length). Older lenses had this red point on it which indicated the necessary shift for IR! Theoretically one could also use the AF with the attached filter. Sadly AF needs a lot of light to work properly and a lot of light is exactly what you do not have with that filter in front of your lens. So forget the AF and focus manually. Exposure Most cameras will produce much too dark results if you try to use the automatic exposition control. So switch to “M” and try it out until the histogram is reasonable, that means: not blown out and not completely at the dark end. For my Canon 5D I have some values to start with for bright daylight: f/13, 10s exposition at ISO 160. Something like that. It depends a lot on the amount of IR in the light. High ISOs won’t work. At long exposition time all CCDs tend to produce a lot of noise and when taking the pictures with high ISO values too … I never use more than ISO 200 here (although I often use ISO 3200 on Rock concerts at short exposition times for example – no IR of course) Reflexes The better the filter, the less reflexes. The Hoya is of course a expensive and coated glass product whereas the Cokin is a rather cheap peace. But IR filters with M82 are about 180,- EUR and so my largest is M67 (about 90,- EUR) which is ok, when I use the longer focal length of my 24-105 zoom. You can minimize reflexes by covering your gear from direct sunlight – in fact, you should do this! Also cover the view finder from light from behind during the exposition. Polarizing filters in addition sometimes help here but double the exposition times. The process
The photoshop part, which is at least that important, is available only in the word document (screen shots). This is a word document I wrote today, so I may be able to post it sometime, soon. Gunter. infrared 
ir 
Trackback(0)
Comments (4)
  written by mmmee, June 27, 2007  written by guenterleitenbauer, July 05, 2007
Nice to hear that. Keep on trying. IR is always some kind of trial and error and the results are never 100% predictable which makes this so interesting.
written by a guest, October 02, 2008
hiya
written by a guest, October 02, 2008
munch ke
Write comment
|
|
| Last Updated ( Sunday, 24 June 2007 ) |
TrackBack URI for this entry
Subscribe to this comment's feed
| < Prev | Next > |
|---|
After receiving my Hoya R72 filter, I dithered for a long time about having no time to get out and try it.. if the truth were to be told -- I was in fear of failure with my new filter.
After reading your article over several times, I finally went out and tried it. Was fun and I did have a bit of success, but I need to practise some more yet.
Thanks so much for the article.