Sky Flats and Uniformity

Rafael Sampaio

When doing automated sky flats during dawn, some narrowband subs seem not to have the same brightness of others, even if the filter is identical. . Do WBPP compensate for that?

BlockHead

Hi Rafael,

The sky brightness is changing every second- so the light levels will be changing for each picture. For some filters where the exposure time is shorter- that change in light level may not be as obvious...but it is there. 

Having flats at different light levels is not an issue. It is commonly misunderstood that the light level of a flight is a critical value. This is not true. When you stack your flats you will be obtaining an average light level. You want enough frames to reject stars from the images. You might not be able to take flats for all filters during a single twilight session (you typically want to combine 5-7 flats per filter at a minimum.

So WBPP doesn't do anything to "compensate"...because there isn't anything to do in particular.

-the Blockhead