View Full Version : Some Qs for you all who shoot the cosmos.
8th of January 2009 (Thu), 11:20
I didn't see a sticky here, and not even sure if this is correct place, but I figured if anyone knows the answer, they would be here.
I wanted to try and do some shots of the stars. Lately here has been quite warm, so night time shouldn't be so bad. I'm going to drive up north to where it's more country to avoid light pollution and what have you.
So, my question is, should I leave noise reduction on? I mean if I do a 10 min exposure, the NR will take 10 min. Is there any big pros or cons to using camera NR or doing NR during post? Also where I plan on shooting from shouldn't be any cars, but if a car or two do happen to drive by, what are the chances of their lights effecting a long exposure? I will more than likely have the camera mounted on top my truck, so it should be well overhead.
If you have any other recommendations, please let me know, like maybe exposure times, specific apertures etc. ND filters? Thanks Everyone!
8th of January 2009 (Thu), 11:54
I wouldn't suggest using in camera NR. Aside from the dreadful file writing time you'd be better served to shoot shorter exposure(max of 5-6 min) and stack the multiple exposures using the appropriate software. Am I correct in assuming you're shooting trails around the north celestial pole for the spinning effect? Shooting these length exposures straight overhead won't be all that interesting IMO but you may like them. Shoot at a low focal ratio and 200 ISO or so and see how the first exposure looks.
I would recommend that you shoot from the ground using a solid tripod and use a center weight underneath if need be for stability especially if there's any breeze. If the soil is soft bring blocks for the legs. Shooting from the top of your truck brings the truck shaking from the breeze into the mix. And if it's hot out or you're shooting toward the hood you'll have radiational cooling in your line of fire which can cause image distortion.
As far as car lights, as long as the light doesn't hit directly on your glass then you'll be fine. You could take some black construction paper and some tape an craft a cone shape shade for the lens just in case. Hopefully you can position yourself so that the headlights can't hit the lens. Good luck and clear skies!
8th of January 2009 (Thu), 17:18
Thanks Steve for your input. I completely forgot about how sensitive the camera can be with a little motion. So no NR, got it, the write times can be dreadful for sure!
Do you recommend any particular software for merging photos? I had always though people who did those solid streaks, did it all in one shot.
About the north star, I wanted to put in the corner of the photo or something. I think one stationary star there, and all the rest going around it would look interesting. I guess I will have to just shoot and see.
8th of January 2009 (Thu), 18:54
As far as NR, you can shoot "dark frames" and subtract them from your image(s). These are images shot at the same length and ambient temperature as your light (image) frames. There is software for stacking star trail shots here (www.startrails.de/html/software.html) that will give much longer streaks without washing out the sky backround due to extremely long exposures.
I use a program called Deep Sky Stacker (free) for non startrail shots. It has the capability to subtract darkframes and stack light frames as well as other capabilities. Not sure how it would work on startrails though.
Good luck and clear skies! Post up what you get when you do it!
12th of January 2009 (Mon), 03:13
Because of the beauty of stacking I see no point in shooting extremely long exposures for trails. If you really only want to shoot one photo, then drive home, the Noise Reduction setting is fine because it can do that while you're packing up and driving. But if you want to shoot several exposures and stack them, then each shot has got to start as soon as possible after the previous one, or your trails will be dotted lines.
Some say that the longer the exposure the more stars you'll capture, but I don't think this is true when you're not tracking. There's a point at which the really dim stars won't register on your sensor because they're constantly moving. The only way to capture as many stars as you can would be to open the aperture completely and set the ISO to as high as possible. However, this might bring it too much light pollution. It's all about what you yourself prefer, and only by experimentation will you get the best results.
Good luck and let us know what you manage.
12th of January 2009 (Mon), 04:15
Still have yet to get out...Maybe tomorrow?
I will do the stacking then. I don't feel like driving way out there, then take one shot and drive home :)
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