# Long exposure noise reduction



## Joefbs (Aug 6, 2014)

What are the disadvantages of using this function? If it reduces noise, then why wouldn't you keep it on all the time during exposures longer than 1 second? Do you guys use this feature? Does it make that big of a difference? Would love to hear what you guys have to say.


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## SnappingShark (Aug 6, 2014)

For me, if I take a 1 minute exposure, it takes a further 1 minute to remove the noise.

So it doubles the time taken.

TPF members helped me figure that one out!  
That's my only downside.


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## Joefbs (Aug 6, 2014)

BrightByNature said:


> For me, if I take a 1 minute exposure, it takes a further 1 minute to remove the noise.
> 
> So it doubles the time taken.
> 
> ...




So you would say that it is a function worth using as long as you are ok with the extra time needed to process the image in camera?


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## SnappingShark (Aug 6, 2014)

Joefbs said:


> So you would say that it is a function worth using as long as you are ok with the extra time needed to process the image in camera?



Personally, I can live with it. Yes. YMMV though!


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## Overread (Aug 6, 2014)

Long Exposure Noise reduction works by taking two exposures. First is your normal exposure, second is an exposure taken with the shutter blades fully shut and take at the same ISO and shutter speed settings as the original first shot (aperture doesn't matter because the blades aren't letting any light from the lens in). 

It then deducts any colour/noise in the second shot from the first. 

It's designed to remove noise generated by heat on the sensor, a typical problem when shooting long exposures over 30seconds. As such its only any good at removing this heat generated noise/dots because any regular noise is unlikely to show up in an exposure with no light contributing to it. 


So for normal shooting its effect would be marginal to nothing.


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## Joefbs (Aug 6, 2014)

Overread said:


> Long Exposure Noise reduction works by taking two exposures. First is your normal exposure, second is an exposure taken with the shutter blades fully shut and take at the same ISO and shutter speed settings as the original first shot (aperture doesn't matter because the blades aren't letting any light from the lens in).
> 
> It then deducts any colour/noise in the second shot from the first.
> 
> ...




Awesome! That makes sense. Thanks for the explanation!


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## jsecordphoto (Aug 6, 2014)

I only use it when taking long (1minute +) foreground exposures at night. If I don't I end up with tons of hot pixels


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