Infrared photography - filter or conversion ?

A few thoughts on infra red DSLR photography.  When I saw the images produced by infra red with white vegetation and black skies I wanted to have a go myself.  A "normal" DSLR has a filter on the sensor which passes visible light and blocks infra red to create good visible light images. A bit of online searching suggested that if a camera could "see" the light from a TV remote control, it could take infra red photos. I tested my 2 Pentax DSLRs and found that the K7 showed a bright white light and the K5 a pale orange glow when I pushed the remote buttons. This suggested that the built in infra red blocking filter on the sensor was less effectivwe on the K7.  

I spent £30 on a P007 Creative 720nm filter for my Cokin P holder and I was set!

I got some reasonable IR images with this filter (if you have Dxo Filmpack, try cross processing!). It is a cheap option but there are issues. The biggest problem is that the filter is very dark and when combined with a built-in partial IR filter very little light reaches the sensor. The image is too dark to frame with the viewfinder and long exposures and/or high ISOs are needed even in bright sunlight (the best conditions for IR photography).  It is necessary to guess the framing and focus manually or frame (and focus) the photo and then insert the filter (you are using a tripod for the long exposure anyway). Exposures longer than 10 seconds are not unusual - not good if there is any wind though.

This image was shot at 1/15s, f2.8, iso1600 using an external filter

This is the same image cross processed in Dxo

The alternative is to have an old/spare DSLR converted for infra red photography - old cameras have almost no trade in value and the conversion on the K7 cost me £250.  The difference is chalk and cheese. With a 720nm internal filter conversion, the camera works almost exactly as a standard DSLR, except that it only shoots infra red. Auto focus, internal metering and framing through the viewfinder operate normally and I can take images in daylight at 1/250s, f8 and iso200 - no more tripod or guesswork. 

This image was shot at 1/160s, f11, iso200 using the converted camera

Are there any downsides? Well, you need a body to convert, and then you need to carry the extra weight if you plan to do visible and IR photos on the same shoot (but many APS-C bodies don't weigh much). Check that the lens you want to use will be effective for infra red, ACS has a list of unsuitable lenses on their website.

There are options on the filter installed - from clear quartz to around 850nm hard infra red. 

In theory, clear quartz allows you to shoot visible light but passes infra red so that an external filter works better, 850nm will only give you a monochrome infra red and the others (680, 720 etc) allow some colour but are mainly infra red, These are more suitable for some post processing effects, Google colour channel swapping for examples. Lightroom doesn't have channel swapping facilities but there are somespecial presets available for download, or look for Photoshop tutorials, or GIMP.

Have fun 

JB