We installed a “flat panel” for the second pier (Pier 2). “Flat field correction” is another facet of image calibration in astrophotography and attempts to remove artifacts and other aberrations that occur as light travels though your specific optical train. These could be anything from dust to stray light or shadows occurring due to various equipment components and set-ups. The goal is to achieve a uniform field across the target image. The “flat field” is itself an image of a uniformly lit area which when exposure is adjusted properly, yields a “flat image” showing the artifacts present in your set up. When you subtract this image from the actual astronomical image, the result will be (hopefully) a clean image of your galaxy, nebula etc. Several options exist for a uniformly lit target to produce adequate flat frames. For pier 1 up here at the observatory I use what are called ‘sky flats’. At dusk or dawn if it is clear there is a region of sky where brightness is uniform. The 16″ scope routinely takes these sky flats before and after the imaging session. They work very well- when it’s clear. The other potential issue is that you have to keep changing exposure times as the sky continues to darken or brighten during dusk or dawn in order to maintain the same peak intensity of your flat, typically 40-70% of the saturation point of your sensor. While this exposure adjustment happens automatically with the control software for Pier 1, at some point it either becomes too dark or too light in the sky to continue so you will always be limited with the numbers of flats you can acquire using the sky flat method.
Enter the “flat panel”! This is a really neat device which is a uniformly lit artificial light panel where you can adjust the brightness until you have reached the desired level for your equipment. Then you can fire away and take as many flats as you like whenever you want! I decided to try this out for pier 2 and I have to say it works very nicely. Now it may be difficult to automate this feature because the flats in this case are obtained when the telescope is in the parked position and the imaging session is completed. However it is easily carried out through a PC software interface and thus can be obtained remotely!
“Spika flat fielder” is available through a company called All Pro Software and is very easy to set up and use. I purchased their standard panel which is about 15″ and can be used for scopes up to 12″ in diameter. Larger ones can be purchased for bigger scopes if needed. I modified an artists easel to accommodate the panel and this enables me to move the panel around if needed. A standard AC power converter enables a usb connection to your PC and also powers the panel. The software control is quite simple. An example of a flat frame is shown below.
Happy Flat Fielding!
Thanks for reading!