[jezza323]

I went out to the airport last night to get some "plane trails" and im a bit concerned about the amount of noise in my shots, especially given they are just 30 sec exposures @ ISO 100

Here is a 1:1 crop of the night sky taken @ ISO 100, 30 secs

Is this a normal amount of noise?



this is an example of the image the crop is from - been stacked already though

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Last edited by jezza323; 04-16-2009 at 10:58 PM.

[Tom S.]

Yes. No matter what the exposure settings, you should not end up with a Red X.

[DAZ]

Much more information is required to reach an informed (or even pretend) opinion.

DAZ

[jezza323]

like what information?

[DAZ]

like what information?

Was dark frame noise subtraction turned on? It was a 30 second exposer dark frame noise subtraction might have been needed. Did you shoot RAW or JPG? Some RAW converters will map out hot pixels. Did you have any in camera NR turned on if you shoot JPG? Did you brighten the photo any? All digital cameras have some noise. If you have a very dark frame and you brighten it you will amplify the noise that you may not be able to see in a brighter photo. This is because the signal to noise is so much greater. In a brighter photo the noise is always there but is hidden by the signal. Are the bright pixels in the same place in any other photos you took at about the same time? There maybe some hot pixels that need to be mapped out. There is not a totally complete EXIF data. Some was striped out and some was left in. It is kind of hard to tell if from the EXIF data some of the above that could normally be in the EXIF data.

DAZ

[jezza323]

that is straight off the camera, opened in picasa, cropped and uploaded, not lightened up at all, shot in JPG, although later in the evening i shot RAW, which also shows the problem. in camera NR was disabled (as i was planning on stacking afterwards i needed short time between shots). i will try opening the original in lightroom over the weekend as i believe it automatically maps out hot pixels?

[Lowell Goudge]

i actually think the shot is pretty good, you can even see the strobes flashing at defined intervals on each trail.

[DAZ]

A hot or stuck pixel when converted to JPG may make it look bigger then just one pixel. With Dark Frame Subtraction it will get rid of stuck pixels, most of the hot pixel noise and a lot of thermal noise. A RAW converter can map out the stuck pixels and help with the hot pixels (not as much as DFS) but will not do anything for thermal noise.

If you are pushing the camera RAW is usually the better bet but JPGs is some times easer to work with if it can get the job done. For things like this you can take your own dark frame (1 at the start and 1 at the end) and do DFS PP using the frame closes (gives the best results) to the photo you are processing.

For a photo without DFS into JPG it looks pretty good. About what my *ist DS looks like if I don’t use DFS. With DFS you may even see that some of the pixels (most likely the white ones) are stars.

DAZ