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05/07/2004 02:14:24 PM · #1 |
I love playing around with long exposure shots but once I get to around 2" ISO 100 with my Olympus c-400, the picture starts getting grainy. when ISO is at 400, it shows up around 1/2 second.
I can't find the photo again, but I remember one from DPC where the photographer left the shutter open for several minutes. It captured the night stars travelling a few degrees through the sky. A structure in the foreground revealed the warm glow of a small flashlight shining at the roof. It was an awesome picture... and clear as a bell.
What the difference between my camera and theirs... what should I look for in a camera if I want to take some long exposure shots?
Message edited by author 2004-05-07 14:15:19. |
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05/07/2004 02:33:25 PM · #2 |
If you type in noise in forum search you should be able to find more info on your problems.
Also check into software like Neatimage or NoiseNinja that may help a little. |
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05/07/2004 02:44:07 PM · #3 |
The amount of noise in an image is dependent on several factors. There are two sources of noise, thermally generated electrons in the image sensor and those generated in the amplifying electronics.
Thermal noise is dependent on two factors, temperature and time. If you wish to reduce noise at the source, you must reduce temperature and length of exposure. To reduce noise after the shot, use a noise reduction software application such a Noise Ninja or Neat Image.
Another method to reduce noise is the 'dark frame' method, wherein you first make an exposure with the lens covered at the ISO, white balance, and duration of the intended shot. Then take the shot and subtract the dark frame noise from the real image. The dark frame method is preferred by astronomers but is cumbersome to apply.
Most digital camera users that are serious about noise reduction use a combination of methods, ie. short exposure, low ISO setting, and post processing software. Keeping your camera cool is also effective. Hope this helps.
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05/07/2004 05:03:45 PM · #4 |
| Thanks, guys... that's good advice. The Dark Frame technique sounds terriffic... and obvious... one of those... "why didn't I think of that" kind of moments. Thanks, ElGordo (which means, "The Gordo" in spanish) |
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05/07/2004 05:19:20 PM · #5 |
subtract the dark frame noise?
not sure i follow what you mean here.
Originally posted by ElGordo:
Then take the shot and subtract the dark frame noise from the real image. |
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05/07/2004 05:21:42 PM · #6 |
Originally posted by lbWhaples:
Thanks, ElGordo (which means, "The Gordo" in spanish) |
That's what my username means too :) |
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05/07/2004 08:14:02 PM · #7 |
Originally posted by soup:
subtract the dark frame noise?
not sure i follow what you mean here.
Originally posted by ElGordo:
Then take the shot and subtract the dark frame noise from the real image. |
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There are two types of noise to deal with. First there is "fixed pattern" noise. The noise pattern is the same for every shot (it does change over time as the sensor ages, and changes in magnitude with temperature). If you take a pic with the lens cap on immediately after your normal pic, you can subtract the "dark frame" and essentially eliminate the fixed pattern noise.
The other type of noise is random noise, pattern is different for each shot. You cannot subtract this out, since you don't know the pattern. you can average it out, however. To do this, break up a long exposure into shorter ones. For example, take a 120s exposure and make it six 20s exposures. Adding them together will produce a much smoother image than a single exposure. Old trick from astrophotography.
Message edited by author 2004-05-07 20:15:09.
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