Infrared Picture Set with Pentax-M 20mm f4

For some reason, I have been itching to bring out the Infrared modified camera and shoot some IR pictures. The weather has been finally cooperating, and I took this opportunity to try an autofocus lens with the 20D. It's a known fact that IR spectrum affects the focus point; most camera's AF system are calibrated for visible light and if you take a picture with the default AF, the picture will come out blurry. For this reason, AF lenses are not very good for IR work, as you would always have to focus it abit behind the indicated focused point. For lenses with USM that support full time manual focus, this is much easier, but still, it's hard to know the exact amount of focus shift you need to do in order to attain critical focus.

I tried the Canon 16-35mm f2.8L II lens today with various degrees of success. For starters, this lens is not a good lens for IR. It has a large hot spot in the centre of the frame, even when there is no stray light hitting the lens. Almost all Canon USM lenses allow you to focus beyond infinity, and that's what is needed to achieve infinity focus for IR. Most pictures turned out to be in focus when the lens was set beyond infinity to the maximum allowed. This is good for pictures that focus to infinity, but not too good if the focus distance is closer. Some experiment is required. This is the reason I like using manual focus lenses, especially the Pentax-M 20mm f4, for IR. When set to infinity, everything is pin sharp from a couple meters away at small apertures.

Redpath Sugar Refinery in IR - Canon 20D IR & Pentax-M 20mm f4. Click for larger.

The cemetery - Canon 20D IR & Pentax-M 20mm f4. Click for larger.

Geese - Canon 20D IR & Pentax-M 20mm f4.