Red Infrared, R-IR, Photography

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 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 www.maxmax.com/, is shown below for the technically minded.

Canon 40D Spectral Response by Okavanga

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 (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.


Victorian IR 1 Mount William Trees by Okavanga   Victorian IR 3 Lake Wendouree Tree by Okavanga

More recently, I started to experiment using a Cokin red filter. Those initial experiments lead to images such as the one below, in which unexpected colours started to appear. I tracked this down to an anomaly in Canon's Digital Photo Professional software, and I dubbed the effect, again with due modesty, the Okavanga Effect as described here ==>
okavanga.deviantart.com/journa….

Filter Frolic IR 2 by Okavanga

I have now gone back a step and have started to use the red filter technique in a more traditional manner to explore how it might be useful in creating and modifying infrared photographic effects. As both red visible light and infrared light are involved, this type of imaging might usefully be called Red Infrared or R-IR for short. I'm not the first to use such a technique, although others use a conventional glass red filter, rather than a Cokin one. Glass filters affect equally both infrared and visible light whereas the so-called "organic-glass" (i.e plastic) Cokin filters allow favour infrared light.

The procedure I use is quite straightforward. The camera has a custom white balance set for infrared only images. The filter is set in place and shots taken normally using manual mode so that I can adjust shutter speed easily. I have used an aperture of f/8 where I can. Because the white balance is set for infrared only, the images have a natural red cast, but only where there is a lack of infrared light! Otherwise, as with the Okavanga Technique, infrared light effects - "white" foliage etc. - dominate. Some results from landscape studies are shown below.




Bruntis Loch by Okavanga

Ross by Okavanga

Torrs Loch by Okavanga

Some points are worth noting. First, I have not used any channel swapping in these images, channel swapping being a technique much used in infrared work. The post-processing has been minimal - some balancing to ensure a "white" appearance to foliage, and some local contrast enhancement to give a bit more impact.

Second, where there is a lack of infrared light such as from sky and sea, then the deep orange-red cast can be effective in adding character to the images - not necessarily to everyone's taste, but nevertheless, a tool worth having.

Third, in contrast to pure infrared work, different types of foliage appear to be better differentiated - see the trees in the Bruntis Loch images. Coloured foliage - flowers and so on tend to become yellow orange, but I shall be posting more about such images later.

Overall, R-IR images obtained by using a red Cokin filter on a full spectrum camera can be thought of as seeing the world as it might appear if our vision was tuned to the read and infrared wavelengths of the spectrum (about 550 - 1000 nm) rather than the visible range.



UPDATE 27 June 2014 FLOWERS

I've posted a set of images taken under in same way as the above images, but colour (white) balanced for effect. Flowers can be made to look white through to pale yellow and even blue with appropriate adjustments.



Bourbon Rose R-IR by Okavanga  Wild Rose R-IR by Okavanga   Clematis R-IR by Okavanga





Cheers

David :iconokavanga:

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DavidKennard's avatar
Hi David

Sorry for the very late reply to this article, I haven't had the time to check DA for quite a while, and I'm trying to catch up today. I think you probably posted this article before the last time I checked in, but I must not have gone through my Journal stack at that time. Anyway, on to my point, could you explain a bit more about the difference between glass and plastic filters. If I understand correctly, you're saying that the plastic filters have a lower transmission of red light than the glass filters, but the same transmission of infrared? So a plastic filter will give an image with more IR / less red.

I tried to see if there were transmission curves for the cokin red filter online, but couldn't find anything. I don't have a comparable cokin and glass filter, but I do have a red Polyester filter and red glass filter that I could compare. I don't remember seeing a big difference between them before though. I think I'm going to have to play with full spectrum plus an acrylic ND filter too, as I haven't tried that before.

I'm not a big fan of the Martian red colour skies. I can't really explain why, but I always seem to prefer a blue or yellow sky. I really like those flower photos though.

Dave