Comment by mturmon

Yes, just 0.5nm of spectrum in the instrument used (https://dkist.virtualsolar.org/vanNoortfastcam/, see under “DataSetDescriptions.pdf”).

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.