# Reducing noise in long exposures?



## Restomage (Mar 30, 2010)

I got a shutter release cable for my D90 to do some long exposures at night during the stars. Since i'm shooting with a crop frame camera, it's obviously a lot more prone to noise. I did a 5 minute exposure the other night and even at ISO 200 I got a bunch of noise. Are there any other tips for reducing noise? There was a little ambient light from the city behind me which could have made the grain show up more than it normally would have but if anyone has any reccomendations let me know.


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## Sw1tchFX (Mar 30, 2010)

is it the purple amp noise in the corners? that's normal. 


you need to have long exposure noise reduction on. it uses a dark frame to subtract the noise, but at the cost of detail.


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## KmH (Mar 30, 2010)

Restomage said:


> There was a little ambient light from the city behind me which could have made the grain show up more than it normally would have but if anyone has any reccomendations let me know.


Grain and noise are not the same thing. Electronic noise is random.

Noise (electronics) - Wikipedia, the free encyclopedia


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## astrostu (Mar 30, 2010)

Define "noise" here.  Or, better yet, post a full-size crop portion of the image showing your issue.


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## Restomage (Mar 31, 2010)

Here is the noise I'm talking about:


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## Tiny (Mar 31, 2010)

shoot at a higher F-stop, ISO 100, and a longer exposure. 5 min is not very long for a star trail.


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## Restomage (Mar 31, 2010)

Tiny said:


> shoot at a higher F-stop, ISO 100, and a longer exposure. 5 min is not very long for a star trail.



I know it's not very long for a star trail but that exposure was only about 5 min and look how much noise I got. That's my issue.


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## Garbz (Mar 31, 2010)

There's a trick to this.

Image stacking. Noise is the best friend of the astro photographer. It allows you to extract extra detail that your camera may not have recorded (sounds crazy but it is statistically very clever).

What you want to do is get a program like Image Stacker and then do maybe 10 30second images. For the final image use the "add" function. Each new image will bring about a new amount of statistically random noise. Therefore when you stack 10 30 second images together you actually average the noise out of the image.


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## Sw1tchFX (Mar 31, 2010)

Restomage said:


> Here is the noise I'm talking about:



This isn't an almost 100% crop is it?

I looked at the EXIF and your exposure was 151 seconds, just over 2 minutes. 

At ISO 200, you shouldn't be getting that much noise at 2 minutes. was it a warm night?

I have a friend with a D300 and he doesn't get that kind of noise even when he's doing exposures that are in the realm of 10 minutes. 

I'd try it again, find a subject that can meter out 5 minutes at ISO 100, and see what happens.


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## KmH (Mar 31, 2010)

I'd take it out of Matrix metering and I would also pick something other than Auto white balance.

Did you turn on Long Exposure Noise Reduction in the camera menus?

As pointed out 151.9 seconds is only half way to 5 minutes (300 seconds).

Looks like you had a bit of wind too.


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## Brick (Apr 2, 2010)

I've yet to take a long exposure with my d90 and not have to deal with at least a little bit of noise.  Maybe we're both doing something wrong.  Anyway, I use noise reduction software.  Some of the most popular are noiseninja and noiseware.  Topaz deNoise has a fully functional free 30 day trail you could give a shot.  They do kill some details but unless you're looking at the full size image it's not bad.


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## the iconic image (Apr 2, 2010)

Before you go out and buy any noise reduction software, CS4 has (if you learn how to use it in advance mode) a very adequate in most cases, noise reduction program built in. I suggest you learn it, try it, and see if it doesn't work for you. As with ALL noise reduction software, you are going to lose some detail. Works better on some images than others obviously.

mike zukerman photography

the Iconic Image


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## den9 (Apr 3, 2010)

i did a 20 and 40 min exposure with a D50, noise reduction turned my purple photos green, or vice versa. the sensor gets too hot. the best solution is to buy a cheap manual film slr.


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## KmH (Apr 3, 2010)

den9 said:


> i did a 20 and 40 min exposure with a D50, noise reduction turned my purple photos green, or vice versa. the sensor gets too hot. the best solution is to buy a cheap manual film slr.


and then deal with reciprocity failure.


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## Garbz (Apr 5, 2010)

Reciprocity failure is something that can be dealt with, digital noise is a pain in the bum.


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## djacobox372 (Apr 12, 2010)

Digital is a poor choice for star photography, go to the local 2nd hand store and buy a cheap nikon film slr (they can be had for $30 or so these days).


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## Garbz (Apr 13, 2010)

Spoken like someone who should go read an astro-photography forum and educate themself


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## KmH (Apr 13, 2010)

djacobox372 said:


> Digital is a poor choice for star photography, go to the local 2nd hand store and buy a cheap nikon film slr (they can be had for $30 or so these days).


Astronomers were the first to really embrace digital imaging and that happened about 40 years ago.


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