5. How to process my astro pictures

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    After taking the pictures, we need to do some extra steps, before continuing in the "photo lab". 
 

 -  Put the lens cap on, so all go dark, keep all configs and shoot some 30 "dark" pictures or "subs". 
 -  Then decrease the time to lowest possible, for my Nex, 1/4000 sec. Then take some 30 more dark subs, kalled "bias". 
 

    A good idea is to flash a flashlight at a single frame/sub between our star series and these "darks", so you see where one set ends and the others starts. Then home to the computer, to download the pictures to a large disk. Myself, I use a 3 Tb USB disk as my photo storage. 
    Making "darks" and "bias" are a minor problem when doing AltAz photos, but if doing GEM, one need to do a set of these for every obs-night. This since 1-30 min exposures enhance any bad pixel in the camera sensor, something all digital cameras has. We also need to do these two sets with the same temperature as the "work" photos. 
    Unfortunately, we're not through yet, we also need a set of "flats", diffuse light frames, to correct any "uneven" light defractions of the optics. 
    Again some 30 pictures, at 30 sec, taken before the light disappear, with the scope directed to the lighter west horizon, with the sun a little bit under it. 
    I use two sheets of milky transparent vellum in front of the scope and then takes my 30 "flats". The indirect sun light creates lighted frames, that during processing is subtracted from the stacked star frames. I use the vellum since it spreads the light and the grain of it are so small that I get a even structure, no grains to mess up with the star photos. Baking paper is translucent enough but has to coarse grain. 
    For storing the photos I recommend creating a primary "Original" directory for the shots and add a sub directory for each photo night, maybe named like "\Original\20130731". Never work with the originals, copy the sub directory to be processed over to a "\Copy" directory structure. 
    It is here important that it's not only a directory link, but a true copy. A failed processing operation can otherwise destroy the originals, have a painfull experience of loosing some of my best Jupiter originals that way. 
    Nutty advices, that above? Why bother, why not keep all in one directory? 
    Well, during a good night I collect some 2-400 frames/subs or equal to 4-600 MB of photos and the processing creates even more files. In three years, averaging 3-5 obs days a month, it has become some 50.000 pictures/1 TB of astro pictures only. 
    The above is the simplest way I found to keep things under control and organized, with a text file telling each object and what sets I taken on it (date and picture series). Since my camera rolls over when taken 9999 pictures, this has became very important. 
    Oh, and for posterity, back it up once ot twice a month to a backup USB disk. MS Synctoy or FreeFileSync is recommended. I have two backups rotating for all my photos, one home in use, the other in my bank safe, rotating once every half year. 
    OK, all pictures now in place, now we can fire up the freeware DeepSpaceStacker. Before explaining, if you running Linux (and maybe Apple iOS), you should be able to run DSS with Wine. I did for half a year. Drawback, under Wine DSS has only 2 Gb memory to work with, so it's quite slow, but surprisingly stable compared to running it under XP. However Win7/8 and +4 Gb makes work a lot easier. 
    Said that, we open DSS. To the upper left, there is some picture opening choices, we start with the dark frames. In the resulting file manager we find our long dark frames, the 30 sec ones. Mark them in the file manager and load into DSS. By the way, moving them to a special "dark/flat" directory helps, DSS will then open the same directory each time. 
    Note: with GEM mounts, use new dark/flats each time, but for us newbies with an AltAz, we're using the same with the matching ISO/exposure time, we used for the star pictures, is a good enough approximation. But we need one set for each telescope/lens. 
    By the way, having done this once, we will see a TIF file in the Dark/Flat/Bias directories. If satisfied with the outcome of our processing, we can use that file instead of the 30 "subs" we used first time. Save some processing time. 
    We repeat this procedure with the "darks" (bias), "subs" and the "flats". Dark "flats" is for the "Pros'". Having done that, we take the top option "Open light frames". In the directory list, we go to the copy directory and chose the photos (frames/subs) to process, that is, one object at a time ;-), but all photos for that one in a serie. 
 

 -  A bit down on the left side is a choice, "Check all". Tick that. 
 -  Then go to "Register all pictures", here is where the processing starts. 

    A little window should appear (if using Wine, ignore the annoying error message - has no meaning), tick all boxes and chose the the "Advanced" tab. It's here we test the quality of our pictures, by counting visible stars. 
    Start with the slider on 50% and press the "Compute" bar. If less than 20 stars, decrease the slide till you have that many, 30-40 is better. If more than 150 stars, increase the slider. 
    Note, sometimes we get a sharp cut off, maybe 60-70 stars on a value and zero at the next. Then we have to accept the lower value. Reason for checking, to many stars increases processing time and can make the program take over 5-10 h. 
    Another note: If a laptop, keep it on a cooling, non-flammable surface or on a ventalating laptop stand giving it air all around, for it will get warm. 
    When we have the right tally, choose the recommended setting button and press"OK" and wait. When it's ready, if you want to experiment, please read some of the more advanced intros to DSS on the net. 
    Anyway, the program will tag along for some time, so if your's doesn't have a iCore5/7 processor, now make some tea or coffee meanwhile, looking in "1001 Celestial Wonders to See Before You Die" or "The Caldwell Objects - how to observe them" for the next 2-3 h. 
    What happens when DSS is ready? We'll see in next article, "6.Astro picture editing"