Canon XSi / 450D Mod

The following sequence of pictures below show the process of removing the Canon #2 IR Cut & Low Pass Filter and replacing it with a Baader UV / IR Filter (400 BCF for Canon 400D / 40D purchased from Alpine Astro (www.alpineastro.com)).  Replacing the filter modifies the Canon camera for astrophotography.  The Baader filter widens the response in the ‘Red’ to allow the Hydrogen Alpha emission line at 656.3nm to pass.  The original Canon filter suppresses this wavelength thus making it less useful for astrophotography.  The Canon Filter also includes a Low Pass Filter which is sandwiched onto the IR Cut Filter.  This is an antialiasing filter / optical low pass filter used to optically ‘smear’ together the red, green, and blue pixels in the Bayer color matrix filter on the image sensor.  The optical low pass attempts to create one photosite out of 4 individual pixels (2 green, 1 blue, and 1 red).  Note – the Canon Low Pass Filter #1 is left in place optically ahead of the replacement filter once the mod is complete. 

Removing the back, disconnecting the cables, and removing the sensor

Camera with sensor removed, Camera & Sensor, Sensor with filters, Sensor with filters removed

Metal bracket that holds filters together, Low Pass Filter #1 separated, IR Cut / Low Pass Filter #2 separated, New Baader UV / IR Filter installed (note color difference)

Filter #1 and #2 reassembled with metal clip, Filters re-installed on sensor, Sensor re-installed in camera, Camera closed up and finished

Diagram showing locations of Filters #1 and #2 discussed above

Diagram showing spectral response of original Canon UV / IR cut filter and Baader replacement filter including location of Hydrogen Alpha line