I've now got the replacement IR filter for my Canon 350D DSLR camera. Last night Pete and I did the filter swap.

Below is the harmless looking package containing a small piece of glass guaranteed to jangle the nerves of an astrophotographer.

Yup, it is the Baader DSLR-ACF Astro Conversion Filter for Canon EOS 350D/20D.

All digital cameras have a filter to block infra-red light. Digital sensors are very sensitive to IR light which humans cannot see. If the sensor gets hit by too much IR then it cannot find an accurate representation of the colours. The colour balance is a joke.

However, for astrophotography the needs are different. We are interested in wavelengths quite close to IR. Close to 6500 we find the nebulae transmission lines of Hydrogen Alpha and SII. The typical IR filter found in a digital SLR such as my Canon 350D blocks over 80% of the red light at these vital wavelengths.

Luckily, several manufactures sell replacement IR filters for these cameras. These allow transmission of almost all SII and Ha light, but block off any longer wavelengths. This mean that the camera is able to operate normally in terrestrial situations with a custom white balance selected, but on the telescope, all the vital hydrogen alpha and SII light can get through.
replacement baader IR filter for Canon 350D part number 2459212
The fun part is of course, replacing the filter. Last night Pete and I (well, mainly Pete) completely dismantled the camera, cut out the ir filter, and re-assembled.

An overview of the process of replacing the IR filter in a DSLR canon 350 for astrophotography is found here.

Detailed Infrared Conversion Instructions can be found here.

I've taken a series of photos of our conversion job, but here is one picture for now.

350d ir filter removal

I am happy to say the swap was a success and the camera works fine. Now all we need is some clear skies.