sky flat flatter than lamp flat

Forums Spectroscopy ISIS flat field vertical gain correction tool sky flat flatter than lamp flat

Robin Leadbeater

OK,  for my setup the profile along the slit for sky flats is flat within ~+-2% but the internal lamp flat drops off by ~20% over the bottom third, presumably due to uneven lamp illumination, so unless this can be adjusted out somehow, it looks like the internal lamp flat would better match the true situation if the vertical gain tool is used. (The narrow dip on the left (bottom) edge is dirt on the slit)