How does long exposure NR work?
Darrell Young (DigitalDarrell)
Keywords: dslr, digital, settings, noise, exposure, iso, d7100, nikon
Many people have wondered about how Long Exposure Noise Reduction (Long Exp. NR) works. To clear up any misconceptions, this article will describe the unusual method the camera uses to remove noise caused by a long exposure. Let’s examine how it works and how to enable it on your camera. (This article is a short excerpt from the NikoniansPress book, Mastering the Nikon D7100).
The long exposure NR works the same way as described here on many of the Nikon cameras, such as on the D5100.
What is Long Exposure Noise?
During a long exposure, the sensor may exhibit more noise than is acceptable. The sensor gets warm after several seconds of use. This warming effect produces amp noise, which causes warmer sections of the sensor to have more noise than cooler sections. This noise presents itself as a fog-like brightening around the edges of the frame. Also, there can be bright spots with various colors at numerous places in the image. This special type of long-exposure noise degrades the image in a different way than the noise from high-ISO sensitivity, which presents as grainy ugliness in darker areas of the image, instead of edge fogging and bright spots in random locations.
Using Long Exposure NR
When you enable Long Exposure NR and an exposure is longer than one second (eight seconds on older Nikon DSLRs), the camera will take two pictures with approximately the same exposure time for each. The first picture is normal. The second picture is a black-frame subtraction exposure, which is exposed for about the same duration as the first picture, but with the shutter closed.
The camera examines the noise in the black-frame subtraction exposure and subtracts it from the first, normal image. It’s really quite effective and beats having to slightly blur the image to get rid of noise, as is the case with High ISO NR.
I’ve taken exposures of about 30 seconds and have had perfectly usable results. The only drawback is that the total exposure time can be as much as doubled because two exposures are made. The black-frame subtraction exposure is not written to the memory card, so you’ll have only one image, with much less noise, in the end. While the black-frame subtraction exposure is being processed, a message of Job nr will blink in any active displays. While Job nr is flashing, you cannot use the camera.
If you turn the camera off while Job nr is flashing, it will keep the first image, but it won’t do any noise reduction on it. If Long exposure NR is set to On, the frame advance rate may slow down a little in Continuous release mode and the capacity of the in-camera memory buffer will drop, usually by one image.
Now let’s see how to configure your camera to use Long Exposure NR.
Enabling Long Exposure NR
The Long Exposure NR setting is found on the Shooting Menu of your Nikon DSLR. Here are the two screens you will see when you decide to configure it on your camera.
Here are the steps to choose a Long exposure NR setting:
- Choose Long exposure NR from the Shooting Menu and scroll to the right (figure 2, screen 1).
- Select On or Off (figure 2, screen 2).
- Press the OK button to save your setting.
Settings recommendation when capturing longer exposures
I like the benefits of Long exposure NR. I shoot a lot of waterfall and stream shots where I want exposures of several seconds to really blur the water. Also, I like to take midnight shots of the sky and shots of city scenes at night. Even though it slows down the frame rate slightly and the in-camera memory buffer holds fewer images, I still use it most of the time. If I were a sports or action shooter using Continuous release mode, I might leave Long exposure NR set to Off. It’s unlikely that I would use exposures longer than one second, and I would want the maximum number of frames per second and the ability to cram as many images into the memory buffer as possible. I would not want my camera to slow down while it processes black-frame subtraction exposures.
Your style of shooting will govern whether this function is useful to you. Ask yourself one simple question: Do I often shoot exposures longer than one second? If so, you may want to keep Long exposure NR set to On. If you shoot a lot of long exposures, compare how your images look with and without it. I think you’ll like Long exposure NR.
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Keep on capturing time…
Darrell Young (DigitalDarrell)
How does Nikon in-camera multiple exposure work?
You might also be interested in learning about Nikons in-camera multiple exposure function which team member Eric Bowles (ericbowles) have written a separate article about, worth reading!
Originally written on July 9, 2014
Last updated on December 31, 2020
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Kathleen SSV (leignkaeth) on May 14, 2015
Hello, I need advice. I have a D7100 body but cant make up what lens to choose. Im more of a landscape and portrait shooter. Please help! Thanks!
John Gamble (jgamble) on January 6, 2015
Does this apply to RAW images or just JPGs?
User on December 10, 2014
Thanks for this information - much appreciated!
Diane L. Simmons (coolmom42) on September 29, 2014
Great explanation of long exposure noise vs. high ISO noise. Also good to know the effect on frame right. Very helpful article.
Andrew Fishkin (asiafish) on September 21, 2014
I have a question. You mention a reduction in frame rate and buffer capacity, does that slowing and reduction occur when exposures are less than one second? I ask because I don't use long exposures too often, but if this mode doesn't slow anything down on short exposures and only kicks in when exposure time reaches one second then I can't see a reason not to enable it. If, on the other hand, it slows everything down always, I'll leave it disengaged and hopefully remember to engage it through the menu when needed. Thanks
Dolph McCranie (Mac4ever) on August 19, 2014
Darell I have a D7100 and have shot many photos with longer than 1 second exposures with the long exposure 'noise reduction off. I didn't notice any particular problems with noise. My question is, does leaving LENR on slow things down when exposures are less than one second? If not it would seem to make sense to leave it on all the time. I have been advised both ways by others.
Dale Maas (marnigirl) on August 16, 2014
Great article Darrell, Just in time for my foray into light painting! I love articles that get to the point without a lot of 'fluff' ;-).
Vic Zubakin (Vitya) on August 2, 2014
Thanks for the article Darrell. I've not used LENR before. I'll try it out on my Nikon D7000. The only drawback I can see is the extra processing time which might be an issue if the light is changing fast & time is limited.
Christian Fritschi (ChristianF) on July 17, 2014
Thanks Darrell ! This is something I had not looked into and your article not only clarifies the topic but also makes me want to try. If I understand correctly, the process only applies to exposures 1 second and slower. The camera's maximum frame rate and buffer capacity remains unaffected for any exposure faster than 1 second. If that is the case, I could simply turn on this feature and forget about it as it would not affect my "normal" shooting modes. Thanks again. Christian.
User on July 16, 2014
Thanks for the article Darrell. Hope to get to meet you when we travel to Knoxville again this coming winter.
Darrell Young (DigitalDarrell) on July 11, 2014
Ralph, Good question! Long Exposure NR is one of the few camera processes that do affect a RAW file, as well as a JPEG. The second black-frame exposure noise is directly removed from the original image. Therefore, it is a change that is saved within the actual image data of the RAW file and cannot be later removed in post processing.
Virginia Tucker (dogmamom) on July 11, 2014
May we see an example of long exposure noise so we can see what you're talking about and compare? I suppose film didn't do this..?
branko komlin (burchan) on July 10, 2014
I did not know this. I should have purchased your book. This is excelent and I am now keen to try it. Thank you Darrell.
ralp hall (rw11) on July 9, 2014
Thanks, but there is one thing not explained here - does it affect only a .jpg or does it also affect the RAW file?