ISO ISO is the way we control image quality. If it's low in good light - at 100 or 200 the quality is brilliant. As it gets darker the ISO needs to be set higher, and there's a loss of quality. Spometimes you cant see exactly why the image is degraded with high iso. t's a genral softeness. Try to shoot bettween 100 and 800.
Before you do anything else - set your ISO to AUTO - and if your camera has an ISO range set this to a maximum of 1600 If it gets dark the ISO will go up and you'll lose some quality but still be able to shoot. Why ? If you shoot in Full Auto or Scene Modes the camera will take over and choose an appropriate ISO for you . In P or either of the semi-auto modes ( Shutter or Aperture ) you can set the ISO yourself but unless you are doing GCSE or A level it's another thing to worry about and best left to the camera to do automatically. When you are more experienced and understand it all you can set it manually.
Why we love Shutter Priority Mode
Which Camera Mode ? You should use Program or Auto in decent light until you learn a little more about your camera's controls - but starting to use TV or S will help you to take control of the camera in low light situations or indoors. .
Shutter Priority Mode TV (Canon) S ( Nikon and others ) is safer in any kind of tricky low light situation because you are in charge of the shutter,and if you have Auto ISO and limit it to 800, you'll still get good quality. Shutter Speeds1/30th is the absolute minimum and if you stand really still that will just about be ok - but only in extreme circumstances. Any movement in the subject will be blurry at 1/30. If you can you should shoot @ around 1/60 - but preferably 1/100 or 1/125 indoors or outside in low light.
Outdoors For general photography on bright days- set the shutter speed to 1/250
Sports Set speeds of 1/500th or 1/1000th - but be aware you also need to set Servo Autofocus and Continuous Drive - or you can use Sports Mode where these will be set automatically as well as a fast shutter. Sports Mode is a lot easier to do in a hurry.
Important If you use TV or S for an indoor shoot, remember to check the speed when you move from one shooting situation to another, or reset to A or P rity