The aim is to produce videos at shortest possible exposure time and fast frame rate in particular when seeing is poor and persistently rolling in clouds are disturbing. Equally important is low noise. Noise can be reduced by choosing the lowest feasable gain and a large number of frames to stack. Naturally, imaging the Moon at good seeing is the best guarantor of success.

Infrared pass filters compensate a lot for poor seeing but need longer exposure times as the camera's infrared response is lower than its visual color response. In case of the ASI290MM, the exposure time with an IR640nm pass filter is about half that of an IR740nm filter -- a significant benefit when seeing is not that bad. When using infrared pass filters on color cameras you would typically record in monochrome.

Infrared filters are used with monochrome cameras or when recording in monochrome with color cameras. Because the resolution in infrared diminishes with increasing wavelength, it is advisable to choose the filter in accordance with seeing. A red filter is often used when seeing is good or even a green filter when seeing is exceptional. Both provide sharper and more detailed images at short exposure times. The unwanted effect of edge diffraction (Rayleigh criterion: 1.22 * wavelength/aperture) increases with increasing wavelength, in that imaging in visual is the better choice when seeing is good and the atmosphere calm. The Gibbs effect, ringing around craterlet walls, occurs where sharpening messes up sharp transitions from dark to light.

 

Lunar landscape captured during calm air with an IR640nm filter. A green filter would have provided a bit more resolution. Celestron C8, 1.6x barlow and ASI290MM camera.

 

Quality IR-cut filters for recording in visual wavelengths pass more than 95% of the light hence hardly sacrificing exposure time. It is a dance on a rope. Either you record in visual light resulting in the shortest possible exposure times and fastest frame rates, or in infrared with longer exposures and slower frame rates, but less prone to poor seeing. When your time and clouds allow, image in both domains and select the keepers after post-processing.

 

 

 

The curves should be taken with a grain of salt as for most cameras the accurate relative response, also specified as quantum efficiency, QE, is unconfirmed.

With Baader UV/IR-Cut Filter

Exposure 2ms, gain 200, 170fps

With Sightron IR640nm Pass Filter

Exposure 4ms, gain 200, 170fps

With Astronomik IR742nm Pass Filter

Exposure 8ms, gain 200, 120fps