If the pixels really are 20x20km, located at 1AU, I get 500k photons (within that bandpass) per pixel per frame at 740 Hz, not counting optical losses.
Space solar instruments like HMI on SDO (https://science.nasa.gov/mission/sdo/) have one or more pre-filters in front of the instrument to block some light far from the passband and keep heating under control. I’m not sure if DKIST has such filters.
If the pixels really are 20x20km, located at 1AU, I get 500k photons (within that bandpass) per pixel per frame at 740 Hz, not counting optical losses.
Space solar instruments like HMI on SDO (https://science.nasa.gov/mission/sdo/) have one or more pre-filters in front of the instrument to block some light far from the passband and keep heating under control. I’m not sure if DKIST has such filters.