I've never done any star trail images before, and wanted to give some a try at SPSP. I didn't know what ISO to use, how long each exposure should be etc, so I just guessed.
23 images x 5 min exposures @ ISO400, with an unmodded Canon 350D on a fixed tripod (obviously). No dark frames or flats applied.
I'm pretty pleased with how it turned out, but I wanted to do more.. My run was cut short by the lens fogging up
Anyway it was good practise for next time. Next time i'll use longer exposures, and take some darks and flats. I'll also use a dew strap on the lens, and i'll use a timer remote (or the laptop).. I didn't have one, so I was running back and forth between this camera and my scope to press the button every 5 minutes I also had to change batteries a few times which caused some gaps when one exposure wouldn't write out to the card because of low battery.
800px version attached. The second attachment was a test shot from the Friday night using Chris' modded 350D, but when the smoke came I had to stop. The third attachment is an example of a ruined exposure thanks to Rod wandering over with his red-light torch and wondering what i'm doing thanks Rod
I really like the first one in terms of overall composition...although the second is good in terms of the area of sky and stars covered. It's interesting to see the Milky Way with one of the MCs down to the right...with all those stars trailing.
Classy shots Mike. Just imagine what they would look like if you did some at the Qld Astrofest. You could start a collection going. "Startrails from Australian Amateur Astronomy Festivals and Parties"
Those are really interesting shots Mike! ..even the 'ruined' one is educational I notice the small gaps between frames (?) in each individual trail... I guess this is the time it takes for enuff photons to register.. also, it's fascinating to see the difference in trail from the SCP to the outer edges of the frame, and the additive effect of overlapping trails.. now if you had two identical cameras, ideally aligned, shuttering at alternate intervals, and interleaved their 'stacks'.. mmmm.... Damn these clouds!! I wanna see that SCP!! Another point that crosses my mind.. longer exposures would effectively 'hide' the lag gaps, I'd expect.. but judging by the length of the trails at 5min, ..something p'haps longer than 20min would be needed(?).. how would this effect the noise and soforth?
Inspirational stuff Mike ..and aesthetically, I like your framing of foreground etc.. lovely 'solarised' outlines.. just a couple of reflections from that nearer light to subtract from it.
Thanks for the comments guys. I really enjoy doing star trails now.. I've bought the $40 timer remote from ebay, and i'll work out how to power the camera off 12v so i'll be able to do more.
Problem is I need to travel to do them - Sydney to the south = skyglow!
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Originally Posted by omnivorr
Those are really interesting shots Mike! ..even the 'ruined' one is educational I notice the small gaps between frames (?) in each individual trail... I guess this is the time it takes for enuff photons to register..
Hi Russ
The gap is the time taken to finish one exposure and start the next, probably with a little time before it starts registering. Ideally I should've done 10min subs instead of 5, to reduce them.
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longer exposures would effectively 'hide' the lag gaps, I'd expect.. but judging by the length of the trails at 5min, ..something p'haps longer than 20min would be needed(?).. how would this effect the noise and soforth?
Yes, 20 minutes would be better, but the noise would increase and unless the sky was really dark, you'd get a lot of skyglow. Ideally they need flats and darks with them too.
Here's a copy of something I put up on a photographic forum a while ago. It lets you perform really short exposures - so in theory you shouldn't need to take darks. I think the package has been mentioned here somewhere before too.
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If you try to emulate the old film camera method of photographing star trails using a digital SLR then you'll quickly come across the achilles heel of DSLR's - limited exposure time.
1) The battery drains pretty fast holding the shutter open for hours.
2) Even at low ISO's you'll start to get thermal noise very quickly - making shots of 5 minutes or more difficult to repair later on - unless you remember to take dark frames and subtract them later or run them through NoiseWare or similar software. This software will process your dark frames alongside your subs too, if you like.
3) You'll start to get the old amp glow happening in the corners. All DSLR's suffer this except some of the newest (40D for example, which turns the CCD amp off until after the exposure is made).
So - how do you take hours-worth of short, continuous images and string them together to form long trails that look continuous themselves?
Try this software. StarTrails lets you take dozens if not hundreds of exposures over a night and then, as JPEGs, lets you select them all and auto-magically combines them for you - remembering to average the background so that you don't blow it out.
This example is one I just took. It consisted of 10 exposures of 300 seconds (5 mins) each. The combines time of celestial rotation is 50 minutes. If I were serious I'd have set up the lappy and asked it to control the camera to take, say, a hundred of these 5 minute frames. I'd have chosen a site that gives me a foreground too - like a row of trees or a building, for interest.
...really informative Mike and Chris!! thanks very much!! ..now something more to be DOING rather than wrestling with the envy monster that inhabits the clouds..
..and CLEAR SKY wishes to all, this International Sidewalk Astronomy Night!!!
Thanks guys, and thanks Chris. StarTrails.de is actually the software I used to create the images above. Really great software - lets you subtract darks, does an ADD for the star trails or an AVG for the foreground, and can turn it into a movie if you want to.
Steve Mogg did a nice movie with very short exposures (hundreds of them) with the camera set up at one end of the field and using a little gadget he made to control the shutter. Check it out at www.moggadapters.com. I reckon it would've looked even better if it was pointing more towards the south, but he wouldn't have got as much of the field in.
Star Trails in the Field
I also had to change batteries a few times which caused some gaps when one exposure wouldn't write out to the card because of low battery.
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