If you look at your interchangeable-lens camera’s menu, you’ll probably find a setting for Long Exposure Noise Reduction. In fact, many cameras have this activated by default. It’s a cool tool, and here’s a simple explanation of how it works and when you might not want to use it.
What’s it for?
When you do a long exposure, let’s say something longer than one second, your camera’s sensor is activated the whole time the shutter is open. As it’s working, it’s also generating heat, and that heat (as well as other stuff) can cause image noise. This noise may show up in your picture as colored flecks of red, green, and blue. These flecks of noise are aggravating, and may just ruin your the presentation of your photograph. Especially if you’re shooting long exposures at nighttime, these flecks may obscure or be mistaken for stars. You’ll usually see the noise in the dark areas of the picture; if there are bright areas, they probably won’t be as noisy looking. (Check out the picture of the ship and dock above)
Your camera’s long exposure noise reduction setting is cool because it helps reduce the impact of that noise. The way it works is that after your camera records the picture, it records another at the same settings picture without opening the shutter. Then it analyses the picture with the shutter closed and eliminates any ‘image’, which would be the flecks of noise that were created by the long exposure. Lastly, it removes the same color flecks from your original exposure.
What’s it mean?
It means that if you have it activated, your picture will by less noisy. Your photo software, like Lightroom or Photoshop, includes noise reduction settings, but they accomplish this by blurring the finest details in the picture. The camera’s method is superior because the fine details appear to be at least as good as the original exposure without noise reduction (at least, on my camera and to my eye; your mileage may vary).
Why would you ever turn it off?
It’s a really beneficial setting, and I’m becoming a big fan of it. There is a HUGE downside, though. This is for long exposures, so image yourself out shooting at night doing a 30-second exposure of cars driving by on the street. Your initial picture took 30 seconds, then the noise reduction action takes another 30 seconds, during which time you cannot make another exposure. It takes 1 minute to make a 30-second exposure. My camera goes as slow as 60 seconds with the built-in settings, and using the app I can shoot on Bulb for any length of time. Well, I once made a 4-hour exposure, which I couldn’t view for another 4 hours. In that instance, I would love to have seen my picture after the first four hours and made changes because the moon came up mid-exposure and ruined it all. However, I had to wait four more hours and only got to make one picture that night.
How do I use it?
My current workflow is to disable long exposure noise reduction, crank up the ISO, get my composition looking good with a ridiculously high ISO and relatively fast shutter speed, then drop the ISO, drop the shutter speed, do a test exposure, make adjustments, test again, then reactivate the noise reduction and make the final exposures.
Doing things this way keeps me from waiting for the noise reduction until I’m sure I’ve got the right composition and exposure time. Obviously, we’re not using this for subjects that are moving quickly. If you’ve got the option, you should add Long Exposure Noise Reduction to your quick menu in your camera so it’s handy and you don’t have to search everytime you want it. I’d also add exposure delay to that menu.
I have to apologize to everyone who’s ever asked me about this setting. I’ve told a lot of people that it’s cool, but it takes a long time, and it only affects the jpeg image, so why not just use the software solutions for your RAW images. I was wrong. This doesn’t only affect jpegs. It works on RAW’s, and I think it probably works better than the software tools. I’m sorry for speaking ignorantly. It’s a cool tool, and if you use it with a little knowledge, it can help you quite a lot. And thanks, camera companies, for making a cool tool that helps us record better quality pictures.