Sunday, April 22, 2012

M100 - part 2

I have decided to try and blog each time I have worked on my M100 image processing project. Maybe someone will find it interesting?

First step was to collect all the files (lights, darks, flats, flatdarks) in one folder; this amounted to 1064 images! Next step is to use MaxIm's 'Set Calibration/Auto Generate' feature to automatically detect and group all calibration frames. I let MaxIm replace all the calibration frames with stacked master frames - the total number of images was now reduced to 204.

After calibrating the light frames and I saved them into another folder. I checked manually to see if MaxIm managed to do the flat field correction properly since I have seen problems with this before. Now, to my great relief, it worked!

Rejecting sub-exposures - on my setup this is typically due to haze and light pollution.
Next step is to load all images for a given filter into Mira and inspect them. Mira is not a well known program these days, but I like the 'image set' feature where you can load and animate a series of images in a single window and measure background levels in a user defined region. In my experience, a combination of background level measurements and visual inspect is the best method for deciding which images to reject and which ones to use. Drifting haze and clouds coupled with light pollution is my most common rejection reason. Today I managed to inspect the red series; out of 29 1200 second sub-exposures I chose to use 17 (see the image with this posting). I do not only reject on the basis of background level, but also if the target contrast is reduced. I rarely see bad images due to tracking issues or wind-buffeting on the AT8RC setup I'm using here. When my initial rejection has been done I'll measure the stellar FWHM in each image with CCDInspector.

Next time I will continue this task on the green, blue and luminance series - stay tuned!

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