Standard digital single-lens reflex cameras must be modified for effective astronomic photography.
To make a Canon 40D suitable for astrophotography, which requires sensitivity to the red light emitted by red nebulae---clouds of dust and gas between stars---one must remove the low-pass, long-wavelength cutoff filter in front of the sensor.
Removal
Certain companies or individuals offer services for removing low-pass cutoff filters on Canon digital single-lens reflex (DSLR) cameras, which requires disassembling the camera body, removing the filter and then putting the camera body back together. It isn't necessary to replace the filter with something else, although not doing so alters the relationship between the lens and the sensor and disables the autofocus function of the camera.
Replacement
Astronomiser, a company that specializes in selling products and providing services to astrophotographers, offers cutoff filter removal and replacement for Canon DSLR cameras, replacing the low-pass filter with one that blocks ultraviolet and infrared light. This option enables the autofocus function of the camera to remain operational.
Comparison
Astronomiser rates filter replacement as a superior alternative to filter removal because it maintains protection for the camera's sensor, blocks ultraviolet and infrared light and enables the continued use of autofocus. Certain models, such as the Canon 40D, along with the 400D, 450D, 500D, 550D, 50D and 1000D, are dual filter models. The rear filter of these blocks ultraviolet and infrared light as well as about 75 percent of visible red light. The front filter also blocks ultraviolet and infrared light, so replacement of the rear filter only retains the autofocus function. Removal and replacement are equally recommended by Astronomiser.
Tags: blocks ultraviolet, blocks ultraviolet infrared, infrared light, ultraviolet infrared, ultraviolet infrared light
