Quote:
Originally Posted by muletopia
So how do you find comets with a DSLR?
Chris
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Typically guesswork for me.
Your star map source needs to be good if thats what you're following. I've yet to find any that is perfect but Starry Nights (PC) and Sky Safari (idevice) are accurate enough.
First thing is before heading outside it I fire up the programs and update with their latest data as comet data changes often with observation data. Next I sketch a simple starmap of the region on a piece of paper, the major stars and distinctive star formations and where the comet is meant to be in relation to them. I do DSLR from a regular tripod with a 200mm lens, so I have to star hop a little to get it pointed to the correct region, I'll take a test shot with a higher iso and longer exposure (expecting trailing) then I can compare that star field on camera to my iphone in Sky Safari, to make sure I have it pointed in the correct general area.
Next I note where the comet appears in sky safari and zoom in on camera image to same location and see if i can see it there, might have to scroll around a bit until I spot the faint coma. sometimes the comet is very obbvious in the frame sometimes its too faint but comes good after stacking/processing. My aim here is to make sure The comet is actually there or if I cant spot it that I am capturing where the software says it should be at that time.
I typically know which way the star field will drift across the sensor so since I'm shooting untracked I try to position the camera such that the comet is to one side of center frame and will drift across the center during my shoot. I then adjust for my actual capture settings and use a remote shutter to run off 100 shots, Then I recheck star position and readjust camera direction if the comet is nearing the other frame edge and repeat the process several times so I get a few hundred shots, usually they all contain the comet with a high percentage near the center of the frame where lens distortions are lowest.
To process in PixInsight I star align the whole lot as first registration to deal with field rotation then a second registration using comet align to "lock" the comet as it drifts against the star field. When I integrate the stars get mostly removed but the comet ends up as crisp as I can get it. Just doing a regular align or only comet align the starfield rotation is still there and if the comet has a tail you smear details.
Sometimes its a matter of point and pray. But stay commited, I screwed up a few times by second guessing myself and repositioning my camera a couple of times to try to get the sky covered and found later I completely missed the comet and if I'd left the camera alone for my usual routine the comet would have just drifted into view.
Comets are often too faint to see on a dslr though they may be there in the raw data. The skyhound maps I started with I found were wildly wrong predictors for me, so was stellarium (if the comet was in the database) but Starry Nights and Sky Safari very very close and give a good enough match to my processed files. So you may need to do a bunch of test runs to firstly photograph a comet and then see what your software tools predict for the location of the comet in relation to the starfield for the time and location of your photograph. Also look at the faintest stars in the photograph and look them up in software to guage what the limiting magnitude is of your capture gear, so you know if you are hunting for a comet around that magnitude you just may not be able to capture it. (using the comet subs you captured do a regular star align and process to determine the faintest magnitude stars you are able to see in the image, if you comet aligned a lot of star data gets lost in processing and becomes unreliable to measure from.) I'm sure theres better and more accurate method to figure out how faint your imaging gear can capture but this does the trick for me (from memory, been a few years, I could go to mag14 and comet chasing bore that out too.
in simpler terms, I Point and Shoot to capture comets
