Blue IR - Tree

Using my Full Spectrum converted Canon 40D, I have been exploring the effect of using a Cokin blue filter to reduce or eliminate red and green light from the IR-Visible full spectrum. These are some of the results. Cokin plastic filters allow IR radiation to pass, while normal glass filters do not.

There are clearly issues pertaining to white balance, and this may be the topic of a further Feature.

Previous Features in this series are :  Red Infrared, R-IR, Photography A while ago, I had my Canon 40D converted to a full spectrum camera, that is the hot mirror that stops infrared light reaching the sensors was replaced by a quartz filter so that the sensors could pick up not only visible light but also infrared. Thus, the full range of response is now from about 400 nm to about 1000 nm. The spectral response curve, courtesy of MaxMax https://www.maxmax.com/, is shown below for the technically minded.

By placing filters over the lens, so different effects can be produced. For example, fitting an infrared filter allows the camera to become an infrared only device - see below left. Using a Cokin (http://www.cokin.co.uk/) neutral density filter cuts down visible light, but not infrared, and so only strong colours show through, such as blue skies, while displaying a typically infrared response from foliage etc.  - a method I call, modestly, the Okavanga Technique - as seen below right.
  The Okavanga Effect v2The infrared images below were taken only a few seconds apart and, with only one difference between them, they have been treated in post-processing in exactly the same way. Yet that single difference has caused the very substantial change in the character, colours, and tonality of the images, with bright yellow areas dominating the visual space. It is this that I call, rather immodestly, the Okavanga Effect.
                         
The images have the following in common. A Canon 40D camera converted to full spectrum capabilities was used, fitted with an R72 infrared filter. The camera was tripod mounted. A custom white balance was employed, this having been obtained by shooting with the R72 filter in place against a standard grey card. Other than the R72 filter, no other filter was used. Light conditions were identical with the shots