Digital InfraRed Photography

I recently bought an Infrared filter for my new Canon 40D in order to try out some non-visible light photography. In this first article I will attempt to explain how to capture IR shots and then in the next post we’ll look at processing methods.

 

The filter I bought is by Kood and is an R72 circular screw in type filter. There are various sizes – I bought a 77mm one for my Sigma 10-20mm. The Kood is a cheaper variant of the popular Hoya R72 filter.

The filter is a very dark navy blue in colour and through it you can see exactly nothing!! The downside to the screw in type is that it is difficult to compose a shot with the filter on. You either have to remove the filter, compose and then put it on, or use a similar technique to night photography – Shoot a few high ISO, max aperture shots first and then stop down for the final shot.

Shooting for B&W

B&W infrared works really well for some subjects and also where there is no variety in the amount of reflected infrared light. Foliage reflects more infrared than the sky, buildings e.t.c. Black and white processing works really well for architectural objects.

The shot on the far left was taken at about 7pm with a bright summer sun shiny behind me. The water doesn’t reflect much infrared light so came out a lovely deep black. The structures have very bold contrasts too, which make the buildings stand out.

White Balance setup for False Colour

For producing colour Infrared shots the most important factor to get right is the white balance. There are various ways to achieve this in post production although none are as good as taking a shot and using that to set the custom white balance of the camera. To do this, set the camera to Auto White Balance and take a shot of a patch of grass. Defocus the lens so you don’t get too much visible grass and make sure the grass fills the frame without any shadow from you or the camera.

The first shot shows a white balance frame and the second shows the histogram data from the back of the camera. Note that the RED channel contains more information that the BLUE and GREEN channels and also at a different part of the spectrum. The white balance frame is the key – You can try clipping the red channel, like I have done here – which will render the foliage very white on the final exposure and also help with the relative levels of BLUE and GREEN in the final shot – which are quite important. I have also tried shots where the RED channel was no clipped and all the channel information was contained within the histogram limits. Experimentation is the key!!

Once you have a shot, set it as the custom white balance in the camera menus. Top tip! Keep a spare memory card with some differing white balance setups and you can try them whilst out on the shoot!

Taking Test Shots

Next up! Shooting.

Manual is best, every time. The way to approach an IR shot is to use the techniques for shooting at night. Start at a very high ISO and wide open aperture, get a decent composed and exposed image and then stop down the ISO and multiply the exposure time up to fit.
Remember a halving of ISO doubles the exposure time, as does moving a stop down in aperture!

I have found that a reasonable starting point for IR on my unmodified Canon 40D with a Kood R72 IR Filter is about 2 seconds @ f/5.6 at 3200 ISO on a bright summers day. For those without 3200 ISO the same would be 4 seconds @ f/5.6 at 1600 ISO. This is a great way to set up composition, check the effects of the white balance adjustment and to gauge a decent exposure. Here, try not to clip the histogram but more likely will be the temptation to not expose enough. Make sure the image reaches both sides of the histogram… Stay at f/5.6 and 3200 ISO but tweak the shutter speed up (or down) to get the exposure. Also its best to manual focus at infinity or between 1m and infinity. Your camera may be able to autofocus through the filter but you won’t be able to see exactly what it is focusing on (!) so its best to focus far and rely on hyperfocal distance to sort you out!

The Final Shot

Once you have the setup you think is best, stop down.. So for my initial conditions of 2 seconds @ f/5.6 at 3200 ISO, that would make 32 seconds at f/5.6 at ISO 200, which is roughly good enough to do 30 secs without getting the remote release out and going into bulb mode!!

From there its 64 secs @ f/5.6 for ISO 100, 128 secs @ f/8 for ISO 100, 256 secs @ f/11 for ISO 100… so it soon mounts up to over 4 mins, just to get a reasonable depth of field! For general landscapes you can get away with f/8, if focused on infinity.

The last thing to do is watch out for the light! I usually go for a subject that has light on it with the sun behind me. This can create problems with the exposure, as visible light can get in to the camera via the viewfinder, especially if the sun is behind you.. Canon provide a viewfinder blocker on the camera strap, just remove the eyepiece and use the cover on the strap to block the viewfinder. It definitely makes a big difference to the long exposures.

Next Time..

Processing stuff! Black and white and False colour tips that I’ve found so far! Enjoy!