Should I prefer raising ISO or lowering the shutter speed in a low light condition?

Question

Example:
1. A "still" object/scene.
2. Night time.
3. The only light source you have is: a tubelight on a wall.

Provided, you want sharpness all around so you won't maximize the aperture.
Flash produces unreal colours (in my case), so I don't use that.

So,
One choice would be to keep the camera on a tripod and lower the shutter speed to allow more light in.
Other choice is raising the ISO (assuming a high ISO does NOT produce noise).

1. Which one should be preferred for what technical reasons?
2. Does either of the choices create a flat light?
3. Do both the choices result in the "same" output?

Answer 1

There is no one answer that applies to every case.

1. Depends on the shake profile and sensor performance (and post processing NR). At some point, ISO noise will decrease sharpness more than camera/subject(irrelevant in this case). And at some point, opening up the aperture will have less degradation than the aforementioned. This of course depends on lens performance as well as shake profile/sensor performance and is probably earlier than you think.

   Guidelines: Tripod? Shutter speed, lowest ISO. Hand-held? start at 1/(35mm equivalent focal length) but take into account IS, how steady you can hold it, if you can lean against a wall, etc.

2. Neither has any effect on light, given that the lights are on for the entire exposure (exceptions being flash, a flashlight, etc.). Long shutter speeds (on a still surface like a tripod) may give the impression of more even lighting because the shadows are not lost in the ISO noise.

3. No, unless your definition of same is different than mine.

Why does flash use unreal colors? You can gel the flash to match the ambient lighting. You can take the flash off the camera to get a more pleasing non-direct-flash look due to placement of specular reflections, highlights and shadows.

Answer 2

Don't be too afraid of higher ISO and the noise that comes with it. For one, when you can't get enough light down the lens, and can't use a slower shutter speed because it would produce an undesirable outcome (enhance camera shake, allow motion blur of objects moving in the scene, etc.), and using flash is not an option, then the only option left is to increase ISO.

Second, even if you have to push ISO to the limit, and end up with a fair bit of noise, removing a lot of that extra noise in post is not that difficult these days. Noise removal software is pretty advanced these days, and capable of removing or reducing a considerable amount of noise before doing so actually affects image quality enough that it actually matters.

If you just can't handle the noise, or you end up with complex forms of noise that are just plain difficult to deal with (i.e. electronic, color, and thermal noise artifacts of a considerable degree), you might want to invest in some additional lighting. You could try getting another, better and more capable flash, along with some gels for color correcting the light it puts out. You might also get a diffuser of some kind to soften the light produced by flash so that it doesn't create harsh and unsightly shadows. Getting a flash arm or simple tripod would also give you more control over how light falls and where it comes from, allowing you to dictate where shadows fall. The benefit of adding your own light to a dark scene is that you don't have to resort to any extreme measures when it comes to camera settings. You can use the aperture, shutter speed, and ISO that fit your needs, or are close enough to them, and not hassle with the problem in the first place.

Answer 3

1. If you are shooting a still subject (as suggested in your question) a tripod/shutter speed solution is advisable. Higher ISO's tend to noisier images. (Noise is also created by poor exposure, so in some cases a faster ISO is the solution, but you are asking about a still object). The tripod and shutter combo will allow your sensor to soak in the light required to create proper exposure while allowing for maximum sensor utility. In other words, pixels are better utilized at slower ISO's; you'll be happier with the result.

2. Unless you are moving outside of the bounds of reciprocity (Way to fast or Way to slow), the quality of light, whether it's flat or not, is all about the way the subject is lit. If you are getting flat light, then introduce some light. This is your credo as a photographer. Control, control, control.

3. In theory, yes and no. Equivalent exposures, within most bounds, will create the same "exposure." However, as you've noted, aperture controls DOF, so the results will not be the same. Super high ISO will not create the same quality as super low ISO. So no, they will not create the same output.

Answer 4

Increasing ISO will reduce sharpness (because of noise and if you do, its post-treatment) and change color rendering (loss of saturation and color change), so to achieve your goal, you may lower shutter speed and put the camera on a tripod.

They definitely do not give the same output.