5 Get creative and try infrared HDR

Adrian Davies reveals the gear and techniques you need to achieve a more otherworldly kind of image

The sensors in modern digital cameras and smartphones are sensitive not only to visible light, but also to invisible ultraviolet (UV) and infrared (IR). Allowing UV and IR to enter the camera for normal photography would lead to strange colours, so the manufacturers filter out the UV and IR at the time of manufacture by placing a UV- and IR-absorbing filter over the sensor, so that it is effectively only sensitive to visible light.

It is possible to have this filter removed

(or remove it yourself) and either replace it with an infrared transmitting filter inside the camera, or place an IR filter over the lens, giving a camera that will record IR images. This is expensive to carry out, however – and, in the case of an internal filter, renders the camera useless for normal photography.

It is also possible to use a conventional unconverted camera for IR by placing an IR filter over the lens. This will remove all the visible (and UV) light, and only allow IR through. Because the camera still has the filter over the sensor to filter out the IR, exposure times will be long – in the region of 5-10 seconds or more at f/5.6. The results may not be as good as a converted IR camera, but will certainly be strong enough to produce some interesting images!

Shooting infrared

You will need a 720nm IR filter (720 indicating that the filter is transmitting IR wavelengths of 720 nanometres). Various IR filters are available such as the Hoya R72, or Cokin Infrared 720 (89B) A007 Square Filter, and various other types can be found on eBay. Neewer, for example, has a set of four 58mm IR filters for under £30. You will only need the 720nm version unless you get a camera converted. Beware of using a relatively thick IR filter on a wide-angle lens – you may get vignetting, as shown below.

IR filters are virtually opaque, so when you put one on the lens you will not be able to use the viewfinder. The Live View facility on many cameras may work, albeit with a rather dim image. It is best to compose and focus, then place the filter on the lens before shooting.

1 Shoot your image with an IR filter

The scene was shot with a 720nm IR filter over the lens, and is shown here straight out of the camera. The exposure is 5 sec at f/5.6, ISO 400. Note the strong vignetting in the shot, created through the use of a thick IR filter on a wide-angle lens.

2 Desaturate the image in Camera Raw

Reducing the saturation of the colours in Camera Raw gives a pleasing result. One technique that IR landscape photographers often use is ‘channel swapping’, where the red and blue channels are swapped in Photoshop’s Channel Mixer facility, to retain a bluish sky, but with false colour vegetation.

3 Edit in PhotoMatix

Three images were shot at 2-stop intervals: one underexposed, one exposed normally and one overexposed. All three were then imported in the HDR program PhotoMatix, where a host of different options is available. This final shot was processed with the Creative option.

Check your lens!

While all lenses transmit infrared light, some produce images with distinct ‘hot spots’ in the centre, as shown in the close-up inset above. There is no hard and fast rule that dictates which lens models do this, and you will need to test your lenses to see if any are affected. There are databases online showing how lenses perform: try www.lifepixel.com/ lens-considerations/lens-hot-spot-testing-database