High resolution imaging of the corona has been pushed to stunning new heights by Miloslav Druckmüller and colleagues. An important feature of their work is more rigorous image processing than what is normally used. Doing this properly results in less image noise which in turn enables more aggressive image processing to bring out subtle details. Still, Miloslavs images do not look overly processed - they just look like the real thing as you can see visually unaided or with a small binocular.
To achieve low noise images it is vital to do proper image callibration; i.e. bias, dark and flat field correction. I do combined bias and dark correction by taking 40 images at each setting used during totality with the lens hood on and the setup covered by black cloth. These are taken just after totality has ended. I use 13 different settings during totality, so this amounts to 13x40=520 images! Afterwards the solar filter and lens hood is replaced by a white cloth, fastened with a rubber band. Using ISO 100 and whatever exposure time gives a signal around 1/3 of full well capacity (typically around 1/1000 sec) I then do 210 flat field images. Finally, 40 more bias+dark frames are taken at the same setting.
This is really boring work and it is done during the remaining partial phase of the eclipse. My DSLR card capacity is 8GB - equal to 296 full resolution raw images. I will be taking 77 images of totality, followed by 770 callibration images! I have two memory cards, so when one is full I'll switch card and start transferring images to my computer using a card reader. In this way the camera will be working non-stop and all images acquired in as short a time span as possible. This is important since the camera noise can vary with time and ambient temperature.
An overview of my complete imaging plan is shown below. I'll be running five Eclipse Orchestrator scripts over the course of one hour - resulting in 847 images. All just to get one - hopefully great - image of the eclipsed Sun!
|Overview of my imaging plan, along with details of exposure settings and what to do when.|
|A typical flat field image. The response variations are ~5% of the total signal.|