edited March 2016 Posted in » Nikon D3100 Forum
Hi guys,
I'm trying to learn how to use the various manual changes, and I'm wondering when should I change the ISO from "auto", and exactly how do I do this in a very simple manner? I appreciate any help offered by more experienced members of this forum.


  • edited March 2016
    If you do manual exposure, and wish to override the camera's meter, manual ISO is actually the only reliable way to do this, since auto ISO will change your settings to match those of the meter if it can, and no exposure compensation is available. In other modes, though the meter makes adjustments of exposure, manual ISO insures that ISO is not one of them.

    To change from Auto ISO you must go to the shooting menu, and there you will find the entry for it. It's not terribly convenient, unfortunately.

    From then on, you will select your ISO manually, either using the [i] menu or with the [Fn] button, if you select that function.

    For myself, I always have ISO on manual, using the front Fn button to vary it when needed. If my chosen exposure mode (usually aperture priority) calls for too slow a shutter speed or too large an aperture, I raise ISO, but try to keep it as low as reasonable, because the lowest ISO gives the sharpest picture with the best dynamic range and the least noise. Once you're used to this, it becomes like a third exposure control along with speed and aperture, and quick to change as needed. But it does not surprise you by changing on the fly as Auto ISO does.

    You should remember that ISO choice is entirely different in P, S, A and M modes. In P, S, A and M, when you switch out of Auto mode, you always set your ISO manually. The value stays until you change it. When in Auto ISO mode, you still set the starting point, but the camera may change it without telling you until later. You cannot use the ISO dial to get out of Auto mode.

    In all the other modes, "Auto" is one of the ISO choices on the dial. In those modes, "Auto" is the default, but you have no starting choice. You can override it with an ISO of your own, but it's either the camera's choice or yours. In those picture modes, you will almost always find "Auto" as your starting point, and if you want manual ISO you'll have to dial it in each time you choose the mode. When you choose a manual ISO in the picture modes, the change is global, and all other modes get it until you change. However, when you change a manual ISO in P, S, A and M modes, all the other modes return to Auto. Go figure!

    In Auto exposure mode no ISO choice is available at all and all other settings of the menu and dial are ignored. When you shoot in Auto mode, whatever ISO it chooses will not upset the manual settings.

    In Auto ISO for P, S, A and M modes, you can also use the shooting menu to select the shutter speed at which the camera changes ISO. If you are using Auto and a VR lens, this might be useful, since the camera's default is 1/30 second, faster than you need for a short VR lens like the 18-55mm kit lens.

    You can also change the maximum ISO that auto will go to, and it's useful to lower this if you find Auto ISO regularly goes up to noisy high speeds. However (this feature is not documented in the instructions) when you set the maximum, that is also the maximum you can select manually when in Auto ISO mode. So, for example, if you set the Auto maximum to ISO 800, you would still find all starting ISO values on the dial, but if you select 1600 as your starting point, it will shoot at 800. The maximum has no effect when you switch to manual ISO, though.

    So, in short, I would go to the menu and switch out of Auto ISO, and then get used to setting ISO manually. It won't take long before you're comfortable with checking your settings and considering ISO as one of them. It does not take long, either, before you get a sense of what ISO is appropriate for what range of shooting.

    There are times, such as when following action in changing light, when you might want to return to auto ISO. In shutter priority, for example, auto ISO will change your setting only if there is not enough light even with the lens wide open. That can be handy if the light level varies quickly.

    It can be confusing at first, both to do and to explain, because many different automatic functions of the camera are abbreviated as "auto". Auto ISO works in two different ways depending on setting. Auto exposure mode is something else entirely, and within the Auto ISO menu is another "auto" setting which varies the turnover shutter speed depending on the lens. Eventually it all sorts itself out.

  • edited March 2016
    Many thanks Bruto.

    ISO manual changes does sound to be a bit complicated, but I will give it a go slowly, while reading through your information.

    Hopefully, once I've "got it", practice will make it much easier and quicker to do. Once again, thanks!
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