what happened here?

[bernhund]

I took this photo in Stockholme a couple of years back. You probably won't see the problem in this particular image, but on the original NEF file the sky and water is littered with tiny red and white spots. When I zoom right in on them, they are little crosses that appear to be made up of 5 pixels. I think there may even be blue ones in there too.
So what happened and how do I avoid it?

[ecsrobin]

It doesn't show.

I don't suppose you had a UV filter on did you?

If not it could be noise from the long exposure image.

[K12beano]

UFOs













(Failing that noise? Care to share the settings?)

[steveatesh]

Sounds like noise to me. Settings and ISO needed ?

[MysteryLemon]

Hot pixels maybe?

Most cameras will have a setting for long exposure noise reduction. Turn this on. The camera will then take a second blank frame after each long exposure shot to cancel out the hot/dead pixels.

LENR isn't the same thing as high iso noise reduction Keep it on.

[Craigwww]

The Nikon D810 had this problem from new, required a modification to lessen the impact of it, was it a Nikon?

[Simpo Two]

Stars...?

[bernhund]

I'll put the iso settings etc. up later when I get home. Camera was D80 if that's of any use.
They're not stars, as I first thought because the water is littered too. Though I expect among them there will be some genuine stars.

[K12beano]

Craigwww said:

..... was it a Nikon?

Hmm - think the clue might be somewhere in OP's reference to "NEF files" - obviously I could be wrong. (So I'll stick with UFOs)


All sensors have to contend with issues around signal-to-noise ratios. Strategies to deal include:

Buying more expensive cameras (man-math will ALWAYS favour this gut-response)

Not turning it up to 11 (i.e. Not expecting the ISO settings to be much more than a marketing hype)

More light

Getting exposure right in the first place - and, if necessary, bracketing where encountering higher dynamic range than a camera can cope with ( the best of the Nikons are up to about 12 stops, but the human eye is good for 24+)

Beating the crap out of it with Noise Reduction in camera (painfully slow process - requires patience and planning)

Or, beating the crap out of it in your favourite software programme from the comfort of your own armchair.

[bernhund]

I'm hoping you're right with the UFOs as it would be much more exciting than my poor camera skills!

[K12beano]

Apart from the particular image settings, what is your software of choice?

I find that the latest versions of Lightroom, for example, give a lot of control. I can find noise in relatively low ISO settings especially going into shadow detail, but depending on subject have a lot of success controlling it - admittedly I'm shooting on a D800 or Df, the latter up to 6400 recently...

[MysteryLemon]

bernhund said:

Camera was D80 if that's of any use.

The D80 and cameras with older CCD sensors are troublesome for hot pixels. I would place my bets on long exposure noise reduction being turned off and what you are looking at is the hot pixels that result. Turning it on will double your exposure time (the camera takes a second exposure of each shot with the shutter closed to use dark frame subtraction to remove the hot pixels) but you'll get pictures without hot pixels. I would prefer the latter.

I owned a D80 and it was pretty bad for it. All older cameras do it and most newer cameras will still do it to an extent.

[bernhund]

O.K, I have moved on from the D80 now to a D7100, so the issue may not occur again, but nonetheless, it's worth knowing what happened and whether it could still happen with the D7100.
The settings were iso 100, 30 sec, f9.