28 August 2007

Dabbling in IR Photography

Infrared photographs intrigue me. Ordinary scenes take on a new look when given the IR treatment and suddenly the mundane become extraordinary.

Recently I took the plunge to try out IR photography using my Pentax K100D by buying a Hoya R72 infrared filter. That R72 refers to the cutoff wavelength where visible light gets filtered out, in this case below 720nm. The Hoya R72 is about the cheapest branded IR filter available, though there are online sellers from China that sell their unbranded IR filters quite a bit cheaper.


I've taken pictures for quite a while now and thought that taking IR pictures would be pretty simple. Was I dead wrong! My initial pictures turned out all red. Not knowing what to do next, I was prepared to abandon all thoughts of dabbling in IR. Fortunately help came in the guise of a friend on the photographic forum Clubsnap. Not only did he gave a detailed walk through of the IR work flow but a hands on shooting session helped clear up any issues.


My initial pictures were taken with the Pentax DA 16-45mm during dreary overcast weather, not the sort of weather conducive for nice IR images. The DA 16-45mm exhibited some hotspots and a washed out centre. Not the most suitable lens for IR.

The images here are from my second attempt using the DA 18-55mm kit lens at the Singapore Botanic Gardens. Surprise, surprise, this lens proves to be excellent for IR photography. One thing to note is that since plants and leaves reflect a lot of infra-red, they will appear brighter while blue skies have little or no infra-red and thus will appear darker in IR photography. All images shot handheld with the Pentax kit lens at ISO 1600 with no cropping using a 52mm Hoya R72 IR filter.


Essentially, taking IR photographs is a 2 step process: taking the image and post processing.

To shoot IR you need your DSLR, an IR filter for your lens and a tripod. The Pentax K100D is in this respect better at taking IR than the K10D. The K100D sensor is more sensitive to IR and allows shorter exposures than the K10D. Setting the custom white balance is also easier.


This instruction applies to the K100D but if you're using the K10D or some other camera, you'll need to experiment accordingly. Thanks to Wee Kiat for the following pointers.

WB Setting
With the IR filter attached to the lens filter mount, take a custom white balance reading of something green (like green grass or leaves) in strong light. Make sure the entire frame is filled by the green subject. Getting the custom balance right makes all the difference in the colours you're gonna get later. There are other methods to set WB that I have yet to try, like using a custom WB filter but this one works.


Shooting
Remove the filter from the lens, compose the scene in the viewfinder, affix the filter again and look at the camera's meter reading. You'll need to do this because once the filter is in place, you'll see next to nothing in the viewfinder. It would be a good idea to use a tripod because exposures can exceed 1 second, depending on the subject brightness, weather condition/time of day and aperture setting.


Setting the camera to full manual mode and using RAW mode is best. Ensure that the exposure combination you set indicates between +2.5 to +3.0 times over the what the camera's meter reading indicate. Using identical K100Ds, my friend and I found out that IR sensitivity can vary slightly from camera to camera. Take a shot. To check if the exposure is spot on, look at the histogram curve on the LCD. It should be kind of even and your image should appear to have a sepia like tone. Bracket if necessary.


Post Processing
The second step relates to post processing. If you're using Pentax's Photo Laboratory, click the grey point setting on something that you know is green in the scene (a leaf, tree, etc.). Save the file. The image then needs a channel swap to give it the characteristic IR look. In Adobe Photoshop, go to Channel Mixer and change the following settings:

1) Red channel : Red 0 Green 0 Blue 100
2) Blue channel: Red 100 Green 0 Blue 0
3) Green channel: Red 50 Blue 50 Green 0 (you can experiment on the red and blue amounts but it should add up to 100)


From here onwards, you can experiment freely by adjusting saturation in Hue/Saturation, curves, add a tone, adjust shadow/highlight etc. limited only by the effect you want and your free expression. For example, the shot above has been post processed a little differently.

IR definitely is fun and the K100D with the kit lens make an excellent combination. Go try it!

No comments: