Worrying about the ISO is silly. You are going to have to use the shutter speed or the aperture appropriate to your lighting conditions. for sports you are going to have to stop the action at an aperture that gives you what you want to be in focus, in focus. For portraits or macro you want the aperture that gives you the depth of field you need. THESE MUST be appropriate in order to get a well exposed and focused image. So let the camera worry about the ISO. It will be what it must be to expose the subject properly depending on the light and the other two parameters. Or use flash.

Bless you, I don't mean to sound abrupt or unkind but this question cannot be answered here - there is neither time nor ability to reach a comprehensive, conclusive answer from 72,000+ people who are not of one mind even if there is only one answer. Why, we even have some people here who are willing to tell you everything they know even though many of them lack the capacity to know anything.

What you're asking is, "is it better to have a bad picture of a good subject, a good picture of a bad subject, or some compromise in between." That's your decision and you have to make it, preferably based on a lot of experience and study which allows you to properly assess a scenario in advance in terms of your capabilities which includes just you, mother nature, and your equipment. What you're going to get here is a repeat of the parable of "The Blind Men and The Elephant" (Google/Wikipedia) but you won't know that because you do not have the vision, capacity, or need to put the pieces you currently have together or you wouldn't be asking the question.



You have to know enough to decide if you want to be a practical person who comes away with the best shot under the circumstances and a willingness to accept it knowing that you've done the best job possible for you, given your knowledge, skill, and your equipment levels, or if you're going to insist on doing it a certain way that causes you to miss a lot of shots that you could otherwise get with a little willingness to compromise being an anal "procedurecrat." It IS your choice. Have the confidence to make it, experiment, and learn from your mistakes which, incidentally, you shouldn't openly display like so many of us do. Obviously, it'd be fantastic if we always got excellent high quality shots of very exciting subject matter, but that's not likely to happen all that much, unarranged, especially if we shoot everything that comes down the pike, still or moving.

My personal philosophy is to get the best shot possible given the circumstances even if it pushes my iso up to as much as 6400 and worry about fixing it later, again, to the extent I can. I'm pretty happy with most of my shots but then, I don't do this to put shoes on the kids, or buy bread, or even beer. Please feel free to check my shots out here by referring to my profile and looking at my last few threads posted if you care to see what about my shots makes me happy. http://www.uglyhedgehog.com/user-topic-list?usernum=1324.

We are not robots, people think differently and to judge people that you have never met is a poor trait. Noise, most people don't want it in a photo but with the cameras that we have today to shoot at ISO 200 or less is silly. Look at the photos posted on U.H.H people shoot from 100 to 1600 ISO depending on light and subject every day, but if you want to stay at 200 or less that is your choice you will miss out on a lot of photo ops. The photo of my friend in his kayak was taken at F-10, ISO 400 120mm with a Pentax Kr. The eagle was taken also with a Pentax Kr at 1/4000 sec ISO 1600 at 400 mm, both photos were taken with a sigma 120 - 400 mm 4.5-5.6. photo was slightly cropped. The camera is an APS-C 12 MP, this is not high end equipment, I have replaced this camera with a Pentax K5ii as my main camera, if I can photograph an eagle from a kayak with this camera at ISO 1600 you should be able to do the same with a Nikon 810.

Exactly. You pick the shutter speed to freeze the action (a blurred shot can be useless) and the aperture to achieve the DOF required, and the the ISO (and noise and DR) falls out wherever for proper exposure. (A noisey shot is preferable to a blurred or out-of-focus shot). I shoot at ISO 6400-10000 with a FF Canon (which is hardly ISO invariant or a high DR body) and the results are acceptable (to me). I would certainly prefer to shoot at base ISO, but the situation dictates the required ISO, which is secondary to the proper shutter speed and aperture.

In principle the low ISO does produce less noise. Every amplification amplifies noise as well as signal.

However, the latest up to date sensors are amazingly noise-free. At a practical level, I can get essentially noise free performance from my Sony a6300 up to ISO 3200. It is noiseless enough to satisfy even some nit-pickers. It will get to 6400 and even 12,800 without serious issues--except in swatches of clear, night sky.

So hypothetically, shooting low ISO is better, and that was true with older sensors. Not so much with newer ones.