Replacing the IR-block filter of a Canon EOS 450D\XSi
The 450D is very much the same as the 550D, the only large difference is that the sensor is seated on shims like the 30D/40D/50D and is not spring loaded. To adjust the position to adapt for changes in glass thickness, you will need to source some precise thickness shims. In this case, we cut some ourselves from a bit of thin plate steel. The basic procedure is:
- Remove the Back
- undo all ribbon cables and ohter connectors (there are lots again)
- unscrew and lift out the main circuit board
- Loosen the three screws on the sensor and lift the sensor out
- Replace the filter and put back together again
The camera in the example was converted using 3mm Schott glass (RG665), this is quite a bit thicker than the original filter layout (total 1.2 mm). We removed the whole filter unit including the plastic frame and reinstalled the filter using a double sided sticker with some thickness to it to make sure the filter would not touch the sensor. The sensor position was adjusted accordingly
Original: ((1.5 – 1)/1.5)*1.2 = 0.40mm Focal shift backwards
New filter: ((1.53 – 1)/1.53)*3 = 1.04 mm Focal shift backwards
Difference to be corrected = 1.04 - 0.40 = 0.64 mm.
because we removed the whole filter unit, there was plety of space to install a large piece of filter glass, this made it a lot easier to cut the filter glass to size by ourselves as we did not have to get the edges right within mm precision. We just measured, scribe and break. Any edges are far enough away from the sensor so not show in the pictures. With this method everybody can do their own conversion easily and you can use stock filters!