Pavilion Spires - Infrared
An infrared photograph of some of the spires of the Prince Regent Royal Pavilion.
An Infrared photograph taken using an unmodified Canon EOS 300D digital SLR.
A 89B/R72 filter was used to block out most of the visible light. This filter appears very dark red, almost black to the eye. The transmission is nominally 720-1600nm.
Each Infrared photograph is a "surprise", but generally vegetation appears lighter, and blue sky appears darker. Human skin also becomes lighter, more translucent/waxy looking, and irises become darker.
The camera has an Infrared blocking filter over its sensor, so a very long exposure is needed. (In this set - with bright afternoon sunshine - the IR exposure times were about 5 minutes, so a tripod was necessary.)
Focusing is problematic. Lenses have a longer focal length for longer wavelengths of light (such as infrared light). Some older lenses with marked focusing distances have a separate "IR mark".
I focused using visible light, and set the aperture to a minimum, to maximise the depth of field and to reduce the out of focus effect. Having set the focus I then mounted the filter. I used a Cokin filter mount that takes square filters. Because of the very long exposures and small aperture used, dust on the filter and lens surface and glare/flare were problems. The optical surfaces need to be kept very clean. (Next time I intend to wrap a dark cloth around the filter system to reduce the effects of stray light).
Less significantly, longer wavelengths resolve at lower definition - for a given aperture size - for physical reasons.
Enthusiasts of Infrared photography can have their digital camera modified - by specialists - by removing the Infrared blocking filter that normally covers the sensor.