MaxMax.com, the people who converted my 350D and will do my next camera, also sell filters. I’ve been testing a number of their infrared filters of late and the first one I will talk about is their unusual XDP filter.
The XDP filter, in a nutshell, lets you shoot false color Infrared Ektachrome-like images on a digital camera. MaxMax is somewhat cagy about this filter, but do say on their site that it is a dual band filter, with one in the infrared around 1000nm and the other much lower (but they don’t say how much lower). From looking at the resulting histograms it is clear the filter is at least dual band.
What you get with this filter on an unconverted camera is an image where the bright foliage comes out red whilst everything else is in the blue-purple range. The green channel has much less exposure.
Exposure is about the same as that required with a Hoya R-72 filter on the same camera. So on the Olympus E-30 this is about 6 seconds, f3.2 and 100ISO whilst on the Canon 400D it is 30 seconds, f5.6 and 100ISO, which are pretty close. This is interesting, because I have found a 1000nm filter seems to need about 5-6 stops more exposure than an R-72 on the same camera body. This clearly shows the addition of another peak somewhere further down the spectrum, which I suspect is quite low in the visible blue part of the spectrum.
The resulting images do need some work in Photoshop and lenses prone to hotspots are likely to show them with this filter. You should use an eyepiece covering or activate the eyepiece blind.
The resulting images are quite striking. Further work can be done with channel swapping, etc, to provide whatever colors you want.
If you use this filter on a camera which has been converted to infrared with an internal filter, such as an R-72, then the result is simply to restrict the IR exposure to around the 1000nm range, giving a longer exposure and a more pronounced IR effect.