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08/16/2011 03:52:45 PM · #1 |
So last night, we had an amazing lighting storm come through. Grabbed the camera and started shooting. Then the shot was over and it would take forevvvvvvvvvvvvvvvvvver for it to come up.
Couldn't figure out why my camera was taking so long. Took me til now to realize the in built noise reduction. (((DUHHHH on ME)))))
So wandering around some star trail shots and came across this.
Half of them use noise reduction in the camera (hence long processing time)
Half of them do not use it and just do it in PS.
~~~
Soooooooooooooo which to use??
Your thoughts??
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08/16/2011 04:06:29 PM · #2 |
Somewhere there is a thread with a lot of discussion of this. I don't have time to look for it at the moment, perhaps someone else will come up with it. Basically, best practice is:
- Turn the in-camera NR off, to enable you to shoot back-to-back exposures
- Combine multiple shorter exposures into your final exposure, for instance 12 5-minute exposures for a 1-hour total exposure.
- Take dark frames before and after your images, and use these to do the NR. Note that you need to average multiple dark frames to reduce random noise in the resulting "master" dark frame.
- Combine your images, which will reduce the random noise (something that the in-camera NR cannot address at all)
- Subtract your master dark frame to reduce fixed-pattern noise (what your in-camera NR normally addresses, but not as effectively)
ETA: remember that when combining frames to reduce random noise, the noise is reduced by the square root of the number of frames used. For example, if you use 4 frames, noise is reduced by a factor of 2 (50%). Nine frames gets you a 3:1 (67%) reduction, 16 frames a 4:1 (75%) reduction, etc.
Message edited by author 2011-08-16 16:09:07.
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08/16/2011 05:20:51 PM · #3 |
I used to use it... Now I don't.... Turns out that the software is better at it and frees me up to do more shooting (and leaves me more battery!)..
I disagree 100% about stacking frames, it generally doesn't look good to me, I prefer a single exposure - more "honest" or "traditional" that way... Of course, shooting in sub-freezing temperatures helps with noise a great deal... |
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08/16/2011 05:53:16 PM · #4 |
| I turned on the noise reduction feature one time and I could not figure out why it was taking so dang long I thought I had broken my camera. Then I remembered I had switched that feature on and promptly shut it off. It took around 3-5 min for the shot to process and with long exposures it takes forever to take one photo anyway, I don't need any extra time added on the end. I really didn't notice any difference between shots. Just use some noise reduction software when you process it. |
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08/16/2011 05:57:20 PM · #5 |
Originally posted by Cory:
I disagree 100% about stacking frames, it generally doesn't look good to me, I prefer a single exposure - more "honest" or "traditional" that way... Of course, shooting in sub-freezing temperatures helps with noise a great deal... |
I used to try it the "traditional" way, but it really wasn't good for noise. Then I started stacking images, and my star trail photos became 10 times as good. Of course, I must warn that stacked images for star trails is not legal in basic or advanced (I assume it would be fine in expert) editing challenges.
I'm not sure why you would think that it doesn't look good, at least for web size. I do agree that there is a very small gap when the shutter it closed between shots that when observed full size, can look a little strange, but for web and small print, I don't think that would be a problem.
Here's a stacked photo taken out a window on the second floor of my house earlier this year: //www.flickr.com/photos/giantmike13/5825983701/in/set-72157625596293739/ |
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08/16/2011 06:14:10 PM · #6 |
I vote for stacking. A dozen years ago I operated the adaptive optics system on the 100â telescope at Mt. Wilson Observatory, and the routine was to take a multitude of relatively short exposures that would later be stacked. Of course, I was collecting data for scientific research, not making pretty pictures, but that makes the point even more. You improve your signal to noise ratio as well as increase the dynamic range of the final image through stacking. And donât forget those dark frames, as  kirbic described. Also makes a difference.
BTW, lovely image giantmike! |
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08/16/2011 06:22:18 PM · #7 |
Originally posted by giantmike:
I'm not sure why you would think that it doesn't look good, at least for web size. I do agree that there is a very small gap when the shutter it closed between shots that when observed full size, can look a little strange, but for web and small print, I don't think that would be a problem. |
You have successfully answered your own question. :) |
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08/16/2011 06:56:54 PM · #8 |
I use my powers to speed up the rotation of the earth, and so have no worries about noise.
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08/16/2011 07:04:54 PM · #9 |
NICE work Mike!
You point out an important advantage of stacking, namely that if a plane flies through, it typically affects only one frame of many, and is easier to remove.
In fact, if a single frame gets FUBAR and cannot be recovered, it's still possible to rotate the sky portion of the remaining frames and salvage the final product.
Cory, if you trigger the shutter again *immediately* after the previous exposure, you will have less than 1 second between exposures, and after stacking there should be no perceptible gaps.
ETA:
Two more advantages of stacking vs. one long exposure:
1.) Foreground illumination can be optimized separately; just set the correct single "subexposure" time to give you what you want!
2.) Really long exposures typically result in a very bright sky background, which has to be adjusted in post. This can be a *real* problem with exposures of one hour or more.
Message edited by author 2011-08-16 19:13:36. |
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08/16/2011 10:43:21 PM · #10 |
| RegiStax is software specifically designed for stacking astronomical images. Haven't used it myself (inadequate hardware) but it's been around for a long time ... |
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08/17/2011 12:30:24 AM · #11 |
Thanks for all the tips kirbic. I'll be on vacation in two weeks and I'm going to do some star shooting.
Great pic giantmike, that's exactly what I want to do in a couple of weeks. |
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08/17/2011 01:19:05 AM · #12 |
I THINK this is the thread kirbic mentioned, though I could be wrong. In any case, there are a host of others out there too. Just do a site search using google for star trails.
ETA: I do stacking, myself. For me, it seems like I get really annoying ambient noise buildup to the point where it's horribly distracting if I don't, even if I'm in the middle of nowhere. It just creeps in from the bottom of the frame in my experience, even if its a smaller city miles away.
One of mine-
ETA2: Even though I was stacking on this one, the glow that you're seeing on the bottom is from a city of 120,000 that's 60 miles away.
Message edited by author 2011-08-17 11:00:15. |
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08/17/2011 08:47:55 AM · #13 |
Originally posted by spiritualspatula:
I THINK this is the thread kirbic mentioned, though I could be wrong. In any case, there are a host of others out there too. Just do a site search using google for star trails. |
Yep that's one of them. As you stated, there are a number of others as well.
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08/17/2011 09:17:02 AM · #14 |
| This is really interesting, thank you all for your thoughts! |
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