CCD and CMOS sensors are very sensitive to near-infrared (IR) light. Although this can be helpful in obtaining the maximum sensitivity, it can also present a few challenges.
When monochrome cameras are used with filter wheels, an IR cut filter is often used because typical blue filters leak in the infrared. Some modern filters include a built-in infrared blocking layer. When performing LRGB imaging, the separate Luminance frame is usually taken with a UV/IR cut filter, to ensure the best color balance. Sometimes, though, the filter is removed completely. This alters the color balance somewhat but provides more sensitivity.
One shot color cameras must have an IR cut filter. Otherwise the infrared light leaks through the color filters and contaminates the images, producing washed out, poorly balanced and saturated images. Unfortunately these IR cut filters cam potentially reduce the camera sensitivity, especially to the Hydrogen Alpha emission line that is so prominent in many nebulae. Cameras built specifically for astronomy have a filter that is designed to pass the H-alpha band. Consumer photography cameras often have poor H-alpha sensitivity. In some cases the filter can be removed, though this makes the camera unsuitable for general photography.
Infrared Reflections
Usually metal parts are anodized black to minimize reflections. Unfortunately most types of anodizing are highly reflective in the infrared. The result is that the camera can see the reflections, but the human eye cannot - which can make diagnosing this issue very difficult. This type of reflection can be most troublesome when trying to perform flat-field calibration, often generating a ”hot spot” in the center of the image.
The simple solution to this problem is to paint the anodized surfaces flat black. This is particularly important for tubular structures just in front of the camera. A baffle can also be added just in front of the camera or further up the optical train to block stray light, but care must be taken to avoid vignetting.