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I have a problem with my D90 I'm unable to figure out. Whenever I take a long exposure with my D90 (say, for 10 or 15 seconds), when the shutter closes again, the info display on the camera reads "Job nr" and the camera is non-functional. If I turn the camera off and back on, it then "saves" the image normally, and pulls up the review photo on the display, as if nothing had gone wrong.

So what's going on here? I don't have any modifications on the camera, I shoot in programmed auto most of the time, and it's a stock 18-105mm lens.

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3 Answers 3

up vote 15 down vote accepted

The "Job nr" is not an error message, it's a status message. You have enabled the in-camera long-exposure noise reduction - the "nr" part of the message.

With noise reduction enabled, after you create a long exposure, the camera takes about the same amount of time to process the image, apply noise reduction, and write image to the card. If you're creating a 15 second exposure, expect about 15 seconds of "Job nr" while the noise reduction is applied.

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So it can be turned off, then, I see. Would you recommend I leave it on? Does it make that much of a difference? I'm sort of an impatient person, and having to wait twice as long per exposure is difficult for me, so I'd rather turn off the NR feature if it's not really useful. –  SpikeX Feb 3 '11 at 16:36
1  
If you're shooting JPG or you don't want to do much fine-tuning in post, leave the noise reduction on and you won't need to worry about it too much later. Personally I turn the feature off and apply noise reduction manually via Lightroom or Noise Ninja so that I have better control over the process. –  ahockley Feb 3 '11 at 16:39
2  
No, the extra time is not spent at processing the image: it's spent at taking a second “dark field” exposure, as explained by Sergey Matvienko. The actual processing (subtracting the two images) is very fast. –  Edgar Bonet Jan 8 '12 at 11:07

It is noise reduction feature. Basically camera just takes another shot of the same exposure, but with shutter closed. Since no light hits the sensor, the only thing we get in this shot is noise - therefore we can substract this noise form earlier image, reducing total amount of noise.

Here is example - 2 shots taken with Nikon D3100 with and without NR at 10s ISO3200:

with noise reduction

without noise reduction

It is clear that first image has significally less noise.

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You may be missing links or sample images here. –  kacalapy Feb 3 '11 at 16:47
    
That's strange - i uploaded this images here. If you are unable to them, here are different links pix.academ.org/img/2011/02/03/… (with NR) and pix.academ.org/img/2011/02/03/… (without). Those are resized images, i may upload full sized photos if you need them. –  Sergey Matvienko Feb 3 '11 at 16:53
    
The downside is loss of detail that you can't control. Also, if doing long night shots, it doubles the time of the exposure which can mean losing out. –  John Cavan Feb 3 '11 at 18:06

Several weeks ago while researching astrophotography with DSLRs I ran across this article about how to do astrophotography with a Nikon. Basically what you are doing above is capturing a truly raw image from the camera (i.e. sans noise removal), as explained below:

The first part is identical to the MODE 2 (noise removal procedure is ON), but for going until the end, it is necessary to turning off the power switch some fraction seconds or some few seconds after the first acquisition phase, i.e. once that the shutter is closed and that the D70 carrying out the dark frame. There is no risk to damage anything. The firmware of D70 automatically saves the image stored in the buffer memory on the CompactFlash card. It is a safety measure if the user cuts off the power supply without taking guard there.

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