Before I really got into photography as a hobby, I kept my camera on the green auto mode pretty much all the time. This way, the camera can do its thing to make sure the photo turns out right…well 90% of the time. The problem was with that extra 10% of the time: I wanted good photos then too. And sometimes I felt like the photos that did turn out okay could have been a little bit better. So I started looking towards the other camera modes.
If you’re used to taking photos in the green auto mode, the next mode you’ll want to learn is the P mode. P stands for Program auto-exposure. It gives you some control over the settings of the camera, while taking care of most of the rest for you. The big setting it lets you change is the ISO.
Back in the film days, the only way to change your ISO (or ASA as it was sometimes called) was to put in a different roll of film. Film with a higher ISO number was more sensitive to light. If you were going to take photos indoors, you used high ISO film so your shutter speed can be quick and thus avoid blurry shots. Outside, you could use a low ISO film because there was plenty of light for a fast enough shutter speed.
So why not just use a high ISO film all the time? Well, that extra light sensitivity comes at a cost. As you step up the sensitivity, you add grain to the image. This reduces sharpness and makes everything look a bit fuzzy. If you look at an older cell phone camera shot in a dark night club, you’ll know exactly what I’m talking about.
Digital cameras are convenient because you don’t have to change the roll of film in order to pick a different ISO. You can set the ISO separately for each photo you take. The P mode on your camera allows you to do just that.
Typically a camera will have a native or base ISO where its sensor works the best. On most Canon cameras, the native ISO is 100. For Nikon, most cameras shoot natively at ISO 200. For each doubling of the ISO, the sensor is twice as sensitive and your shutter speed can be twice as fast. So if you are in a darker room where ISO 100 gives you a proper exposure at 1/15th of a second, bumping the ISO to 200 will give you the same exposure at 1/30th of a second. Most of the time you want your shutter speed to be 1/60 or faster, so in this case you would bump your ISO further to ISO 400 to get the desired 1/60th of a second shutter speed.
The thing is, you can do a much better job of picking an ISO than your camera can. If you keep your camera mode on auto, it will probably try to get the shutter speed to be around 1/60th of a second, and boost your ISO to reach that speed. The problem comes when you are in a darker room and it starts pushing your ISO too high (ISO 3200, 6400, or even higher). You’re going to end up with more noise in your images, and that’s not good.
Maybe you have calm nerves (have avoided caffeine for awhile, etc) and can hold your camera steady for 1/15th of a second while still getting a sharp image. If that’s the case, then you can set your ISO in P mode until you see that your shutter speed is going to be around 1/15th of a second. This will be a much lower ISO than if the camera was trying to reach a 1/60th of a second shutter speed. You’re custom ISO image will turn out much cleaner.
I shot for years all the time in P mode. When I was outside, I would set my ISO at 100 and forget about it. When I went inside, I would start boosting my ISO, but I started to learn how high I could push the ISO before my camera would start producing too noisy of an image. For my old compact camera, that was ISO 400. For my first Canon 450D DSLR, I could push it to ISO 800 and still get nice images. For my 5D Mark II, I can push around ISO 3200 or 4000 and still get solid images.
Once you know how your camera behaves at different ISOs, you can make a decision of whether you should push your ISO higher, or if you should change something else to get a better photo. Whether that means using a flash, putting your camera on a tripod, leaning up against a wall to steady yourself, etc. You now have that extra little bit of control.
Sometimes you have no options but to boost your ISO. The common example of this problem is at weddings when you are in a dark reception hall. In this situation, I would recommend raising your ISO as high as it needs to be to get a sharp image. You’ll end up with more noise, but a grainy photo is almost always better than a blurry photo.