• If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!

View
 

Flatfield

Page history last edited by Joshua Pepper 15 years, 5 months ago

Correct flatfielding is especially important for wide field cameras, since there are strong variations in the image properties and quality across a large field, such as changing transmission with vignetting, the pincushion effect (which refers to a larger solid angle subtended by pixels at the edge of the field compared to pixels at the center), and external factors, such as changing airmass, moon illunination, and cloud patterns across a field.  In addition, flatfields are needed to recalibrate pixel-to-pixel variations.

 

For large telescope with small fields of view, skyflats serve as good flatfields.  Skyflats are images of the sky taken just at twilight or dawn, with no stars visible.  Since the sky background is quite uniform, such images are very good flats.  For KELT, skyflats do not work for two reasons.  First, the sky itself shows structure across our 26-degree field of view, no matter where in the sky we point.  Second, since each of our pixels subtends such a large area (23 by 23 arcseconds), the sky at twilight or dawn saturates our pixels, even for exposure times as short as a second.

 

Because we cannot use skyflats, we instead use screen flats - images of a white screen evenly illuminated within the KELT-S building.  Our flatfield screen is attached to the inside of the roof.  Here are some pictures of the installation.  In these pictures the flatfield has not been repainted to cover imperfections in the surface and the nail heads.

 

 

       

 

    

Once we have repainted the flatfield and set up the illumination lights, we post the resulting images and analysis.

 

Comments (0)

You don't have permission to comment on this page.