I decided to replace the Canon IR cut filter with a clear glass window from Edmunds Scientific Optics. The window is coated on both sides and is close to the same thickness of the Canon filter. With the addition of a .1mm spacer, the focus of the modified camera is returned to that of the original and the camera Auto Focus works.
For astro imaging I will be using a 48mm Baader UV-IR Rejection Filter. The filter can be easily added to the two inch imaging accessories that I use for the camera, including with my 20 inch Starmaster. An “X-nite CC1” color correcting camera lens filter is used for normal daytime photography. A “Hoya R72” infrared camera lens filter is used for daytime infrared photography.
An advantage of replacing Canon’s IR Cut filter with a coated clear glass window is that add-on IR PASS filters can be used for infrared imaging. I tried infrared imaging with a 48mm “Tiffen Red 23A” filter” that I use for observing Mars. For infrared imaging there is a good selection of filters available that block all wavelengths below the color red but allow different amounts of the red wavelength along with infrared. Some of the strongest filters are color black, passing no color but only invisible infrared. The “Tiffen Red 23A” filter that I used for the images below isn’t the best choice for infrared imaging, but because of the modified Rebel’s great sensitivity to infrared, it worked okay.
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