Is it OK to underexpose to get a faster shutter speed, knowing you'll up it later?


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Dec 14, 2011
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I've had a few occasions lately in low light where I decided to underexpose the picture (more than normal) just so I can get a faster shutter speed and avoid camera shake. My thought was that I can up the exposure in Bridge, and everything would turn out hunky-dory.

Is this OK to do? Would any pro do this, given a situation where they can't control the light and they happen not to have a tripod? (Or their subject is moving). Do you lose IQ doing this?
Yes. You gain noise, moreso than if you increased ISO. But in nearly every single situation this is better than image blur. Still, you're better off getting a tripod.

But is it ok? Well. I won't tell if you don't tell :)
Chances are, you loose more IQ than if you were to raise the ISO to gain an appropriate shutter speed for the scenario. Digitally raising the exposure isn't the most "lossless" form of properly exposing your images, contrary to what most believe.
Usually a bad idea. I rather bump up the ISO. Even if the camera doesnt perform as well with high iso.
On my nikon d3100 I ve done some tests and till ISO 1600, it is perfectly usable, and easy to reduce any noise using any noise reduction software without degrading the IQ too much.
At ISO 3200 you start to lose details and can detect color changes. So you might want to test your camera, and see till where its acceptable.

So with this in mind, I know I can go up to 1600 iso. But if its still not good enough, I will defintiely underexpose it, and get it lit up later in bridge. Like said, it's normally better a noisier image than a blurred image. And if it's not badly horribly exposed, you can get the noise away.
If it looks good, it is good.
Depends how many stops you are underexposing. 1/3 stop, you shoot RAW, if you have a D7000, sure no problem. 2/3, still okay. Anymore than that... then you'll really start seeing noise.

And it really does depend on the camera too.

On my D7000, I've done multiple tests to see where the threshold was, I'd say you can recover around 1.5 stops and still have less noise than actually upping the ISO. Anymore than that and it's not worth the trade off. But on my GF2 I can barely increase 1/3 of a stop before the noise goes through the roof and the DR drops drastically.
So good answers here, but in the end it comes down to what is acceptable to you or your clients in the final product.

For me:
#1 is to know my ISO/noise ratio - meaning, get to know where and how far I can push ISO up for a given lighting situation (ambient and artificial)
#2 For a certain shot - will I be able to clean it up in post processing? Sometimes yes and sometimes I just couldn't do it to my satisfaction.

Obviously I am talking about shooting in RAW and I can sometimes push it up a stop or two, even if it is selective areas of the image and not overall.
This is not necessarly "exposure slide", but sometimes I use levels and curves to keep a tonal range or detail in certain areas only.
There is no perfect exposure, rather what looks good or is acceptable as others have mentioned.

Shoot it and see, if you don't shoot, you will never know if you could or could not after the fact.

Oh, and I hope one will not get lazy and start doing this just because they don't want to set up a tripod -
If you're in very low light.. chances are you'll see less noise in the final image by boosting ISO than you will by digitally boosting in post. It does of course depend on the situation...

I often find that if I shoot at gigantic ISO so as to over expose, I can then reduce exposure in post non-linearly, so as to reduce the shadows more than the rest of the image, and reduce noise with them. (hope that made sense). Boosting ISO is a strictly analog process, you still get to use all 14 bits of capture on your A to D converter if you properly expose to the right. Boosting in post later is a digital process, so in addition to the analog noise that you're amplifying anyway, you're also working with lower resolution digitial data since you're not using the top howevermany bits of your converter. Just make sure you're using an analog ISO setting. "HI" and "HI2" etc settings are cheating digitally, so there really is no benefit to them unless you shoot jpg.
I don't like to under expose or for that matter over expose intentionally. I rather adjust the exposure by upping the ISO, since your question said what a pro would do to get the shot. One thing a pro wouldn't do is leave his tripod at home on an assignment. I'm sure that prior experience would have driven that point home. Personally, I keep my tripod in the trunk of my car, so it's always there when needed.
Depends on what camera you have though, if you have camera's sensor with low read noise, theoretically there would be the same amount of noise whether you up it in post of increase ISO. You would get the benefit of non-blown highlight compared to using a higher ISO. That is theory, but practically, you need to decide which type of noise you want - increasing ISO increases shot noise, and upping in post increase quantization noise, the latter is normally regarded as less pleasant but can be removed as easily as shot noise.
I have do it in the past! Back then I did what I had to do to get the shot. Yes, you can adjust for a higher ISO, but you do not need to shoot outside the ISO range that your camera can handle. If you need to do this, then you need to rethink what equipment you are needing for the type of shooting you are wanting to do.

You can however...
  • Accept the lower IQ by going outside the correct settings
  • add light with speedlights or strobes, if allowed.
  • upgrade your camera body
  • upgrade your lens to one that has better glass

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