Most cameras have an IR Cut filter which acts to block IR light from the camera. This prevents IR light from flooding the sensor giving the image a red hue.
For astro photography IR light is useful. Hydrogen gas in nebulas can emit IR light. The human eye can't see it, but the camera sensor (without the IR Cut filter) can, and will be sensed as red light.
If one adds a visible light filter to the front of the camera, then the camera can take images of IR spectrum only.
Nikon and Canon both sell cameras without the IR Cut filter. Also third parties have been able to remove the IR Cut filter on existing camera bodies.
Most cameras have an IR Cut filter which acts to block IR light from the camera. This prevents IR light from flooding the sensor giving the image a red hue.
For astro photography IR light is useful. Hydrogen gas in nebulas can emit IR light. The human eye can't see it, but the camera sensor (without the IR Cut filter) can, and will be sensed as red light.
If one adds a visible light filter to the front of the camera, then the camera can take images of IR spectrum only.
Nikon and Canon both sell cameras without the IR Cut filter. Also third parties have been able to remove the IR Cut filter on existing camera bodies.