Flats inconsistent


I ran 50 flats last night with each filter (LRGB); 5 sec exposures; and all were consistent with the Lum filter; but may were blown out in each RGB series. Does anyone have an explanation for this?

I ended up deleting the overexposed ones before processing in Nebulosity.

Camera: ZWO ASI1600MM cooled; L (1x1); RGB (2x2); High Dynamic setting (Gain 0) and 5 sec exposures.



You can’t use the same exposure per filter and expect them to have the same ADU. For instance, with my flip flat, I take 5 second exposures at R and only 1 second exposures at blue.

Use the calibration wizard to ensure you’re getting the right exposures.


Thanks Mads,

I think I must be doing something inherently wrong in my workflow:

I tried the Flat Calibration Wizard and it took a bit of time to get all the filters to get calibrated.
At my lowest light setting and lowest Gain, I set the Minimum exposure to 0.5 sec and max of 10 sec.

The calibration wizard can save the settings to a Profile or to a Sequence.

In either case, the exposure times are auto-filled and were all lower than 5 seconds.
With the ZWO ASI1600MM cooled, anything less than 5 seconds results in horizontal banding.

Any suggestions how to fix my workflow and the banding would be much appreciated!


You have to dim your light source. You can use a shirt, sheets of paper…


I will add 1-2 sheets of paper on top of my Spike-A-Fielder since it’s already at the lowest setting.

Thanks for your suggestion!