What are the Negatives for Narrowband Imaging?
Narrowband filters are more expensive than LRGB filters. Stars are much dimmer, making guiding behind narrowband filters more difficult. As a result, you may need to consider off-axis guiding, such as with an Astrodon MonsterMOAG, or a separate guide scope, where in both cases, the guide camera sees unfiltered light. Also, narrowband signals are inherently weak, requiring long exposures of 20 – 40 minutes. This requires a mount that is stable over these times with acceptable periodic error.
