What determines the ISO you use for a picture?

Discussion in 'Casual Photo Conversations' started by mark_stephan|2, Nov 5, 2020.

  1. For those of you who choose your ISO based on what you are photographing, how do you determine which one to use?
  2. I go for the lowest ISO I can provided the light available, aperture I want and the shutter speed needed. The exposure triangle. Not that you have to comit exact numbers to menmory, just use your in camera exposure meter.

    I will beak down my thought process.

    1. I look at the scene I want to capture and decide what aperture I am going for. Set the F stop accordingly.
    2. What sutter speed do I need to capture my subject based on is the subject static or moving. Set my shutter speed as desired.
    3. look at the exposure you get in the view finder, is it to the left of center, you are under exposed, raise the ISO.
    If the exposure is to the right of center, you are over exposed, drop the ISO.

    Keep in mind higher ISO can give you noiser images.

    Studio work under strobes, ISO 100 and get the light needed with the strobes.
    At indoor event with bounce and speedlights with modifiers and off camera flash on stands, ISO 400-3200 ISO should provide images you can sell to clients for weddings. But pay attention to your histogram.

    You can go higher on ISO in low light, you could go ISO 10,000, it will be grainy. Very low light with a static image and a tripod, I would drop the ISO to 100 and use a long exposure to get a nice. low light image with no ISO noise.

    Practice, practice, practice...you will get the feel for what is right.

    Just what I do, others opinions may vary.
  3. +1!
    Key thought. - So keep ISO low whenever the situation lets you.
    Do you have a tripod? IS? IBIS? - If not you need a handholdable shutter speed. If yes your subject might still demand a certain shutter speed?
    You might also need DOF, either demanded by the subject or to make sure to get it into focus.
    If my subject can be handled by auto exposure, I might keep my ISO on "auto". Usable auto ISO range is camera dependent.

    To me digital ISO is just a price to pay for available darkness; I can't imagine anything that would look better shot at high ISO, maybe even utilizing ND filters, to get there. But I rather end binning 75% of my pixels than I'd live with lots of camera shake or everything out of focus at f1.2
    Mark Keefer likes this.
  4. Simple: as low as is practical. Raising ISO decreases the ratio of signal to noise and decreases dynamic range. I raise ISO only when circumstances require it. For example, if I am in a shaded area and need an aperture and shutter speed that I can't have with base ISO, I raise it. I also raise it to change the balance of ambient light to flash when using TTL flash. But if I don't need to raise ISO, I simply don't.

    So, my advice--leaving TTL flash aside--is to leave ISO to last. Decide what aperture range and what shutter speed range is OK for the shot you want. If you can't be in those ranges with base ISO, raise it. otherwise, simply leave it its base value and ignore it.
  5. +1 for me too.

  6. SCL


    I typically use either ISO 400 (which matches my film speed) or the lowest available on my camera (200). If movement is an issue, I'll usually revert to a tripod before upping the ISO.
  7. That's what I do - camera is almost always in M mode. Where my settings differ from Mark's: I use AutoISO to take care of steps 3 and 4 automatically. If over- or underexposure is desired, I dial in exposure compensation. Thus I always have the lowest ISO possible for the given lighting situation, aperture and shutter speed. Only when shooting a static scene from a tripod (landscape) do I turn AutoISO off and give ISO priority over the the shutter speed selection (within reason) by setting the camera to base ISO. Studio work (as mentioned by Mark) would be another exception - it's not something I do though.
    bgelfand and Mark Keefer like this.
  8. What Mark said. It really depends on what I'm shooting. If I'm at a race track, where a lot of my time is spent (except for this COVID thing this year of course) I'm worried about shutter speed first, f/stop second, and then ISO to make it work. In that case I'll set on TV, assign a best-guess AV, and let ISO wander. Except after dark, where it always wants to go way over to the dark side at 3200, so I'll freeze it at something like 1500, which is still quite noisy but you can't have it all. Then I set shutter speed and ISO, and let AV wander.

    For most other things I often set ISO at what I think, from experience, the highest setting I can get away with to get acceptable noise and then work with either shutter speed or aperture depending on the subject. An example would be long exposure landscapes which are tripod-based of course, so I can go with a relatively low (say 400) ISO and work with shutter speeds to get the result I need. Basically ISO in digital has allowed us to shoot all sort of stuff easily that would have been a challenge not that long ago. There's a lot of moving parts on the decision so my approach with ISO is to keep it as low as possible.

    I'm interested in what others who shoot events or other "inside" photos do. That's not something I have done a lot, and when I do I struggle with how to get a low-noise shot as I'm sure others must as well. And I'm completely crap on lights and flashes, so still lots to learn there.
    Gary Naka likes this.
  9. "For those of you who choose your ISO based on what you are photographing, how do you determine which one to use?"

    Basically I go by the ISO/ASA I used during film days. That is well-lit (daylight) scenes, I try to stay under 400 and dim lighted areas I try to stay under ISO 800. However these days with modern cameras, especially Full Frame cameras, you can go much higher than that without any discernible noise, or artifacts. For example I often boost the ISO to max 3200 if I'm shooting a wedding or indoors. If I know I'm going to blow up an image to 11X14" or greater, I try to keep the ISO as low as possible because at those sizes, noise seems to creep in. That may mean the use of Flash. Sometimes in bright daylight, where there are a lot of reflective surfaces even the lowest ISO wont allow you to shoot wide open, an ND (neutral density) filter might come in handy to tone things down.
  10. Most of what I shoot is scenery, and 80% of the time I use Aperture Priority and Auto Iso. The shutter speed goes no slower than 1/FL (+/- one stop) whence the ISO is increased as needed. I set the upper limit for ISO at 25,600. In a situation that dark, noise may actually help the ambience (and in my Sony, is surprisingly unobtrusive). In daylight, the ISO will be at its lowest (base) setting of 100 or 200, the aperture at f/5.6, and the shutter speed whatever.
  11. It isn't the higher ISO that causes higher noise. Noise is the result of underexposure and raising the ISO addresses that, and with most digital cameras raising the ISO as a response to the lower exposure lowers an otherwise higher level of noise.
    This depends on the source of the motion blur. If it's you then this answer is correct, but if it's the subject then you need to raise the shutter speed.
    Exactly right.
  12. I think this could be confusing. Yes, increasing ISO doesn't cause noise, but it can make noise appear or make its appearance more severe.

    to oversimplify, noise is random emissions from the sensor or from the electronics that process the signal. Any image has that random noise, as well as whatever signal you have deliberately added. Anything you do to amplify the recorded signal--either increasing ISO or brightening in post--will amplify the unwanted noise as well as the desired signal. Whether it's worse to do the amplification in-camera or in post depends on the camera and the ISO. At high ISOs, it rarely matters. On some cameras, at lower ISOs, raising the ISO is better (perhaps more accurately, not as bad) as brightening in post. But that's a fine point. The main points are that to minimize the appearance of noise, one should generally:

    1. Avoid having to amplify the signal if one can, by exposing well enough that you don't need to raise ISO or brighten in post, and

    2. Related to #1, expose to the right, to maximize the amount of signal in the stored data.

    And before people throw tomatoes, yes, there are times when it's better not do to this. But if the point is to minimize noise, these are the general ways of doing that.
  13. William Michael

    William Michael Moderator Staff Member

    I choose the lowest ISO which will still provide the RANGE of Shutter Speeds and Apertures that I require to make the required Image within any one particular Lighting Set.

    I think it is silly and also dangerous to simply conform to the back of the box film instructions.e.g. - Daytime sunlight 100iso, Indoors 800iso, etc.

    For example shooting fast action in field sports, I have used ISO1600 on a Sunny day when using a F/2.8 Zoom, simply to affect a Shutter Speed range which will freeze subject motion.

    David_Cavan, Gary Naka and Ed_Ingold like this.
  14. Vincent Peri

    Vincent Peri Metairie, LA

    The film box/canister determines which ISO I use.
  15. William Michael

    William Michael Moderator Staff Member

    ^ Probably the best reply possible and very much appreciated.
  16. I choose the ISO/film that will give the results I want.

    On a Fujifilm digital camera, this might be cranking the ISO to 12,800 and selecting the 'ACROS' film simulation.

    On film, this might mean loading HP5+ and push processing.
  17. Just a minor point of order.
    On a given digital camera, the lowest ISO is not necessarily the "best" ISO in some absolute sense. Most sensors appear to be designed around an optimum ISO, which may be at one point or another. Probably the optimum ISO produces the 'best' image in general.

    OTOH, If you want to blur moving water or a carnival ride, ISO 50 at f/32 may be "best". If you want to photograph a moonlit cemetery or a hand-held stellar image then 25,600 at f/1.2 may be your mama.

    IMHO. people need to get rid of their "terror" of grain in film or "noise" in digital imagery.

    Imagine all those early boxing photos without 'grain', for example. Capa's D-Day images clear and sharp?
    Last edited: Nov 12, 2020
  18. In general, as low as possible, while still giving me exposure control.

    BUT, when shooting sports, shutter speed rules. So I raise the ISO to whatever level I need, to shoot at a shutter speed that I think necessary to freeze the action.
    Better a noisy sharp image, than a noise-free but blurry image.

    When shooting a scene, I make what I want the image to be, determine what camera settings I use.
    Just as @JDMvW said.
  19. I agree with Vincent but my box speed is Auto

Share This Page