When taking pictures with most DSLRs on manual to get a picture with optimal quality familiarity with ISO, Aperture and Shutter speed is necessary. All differing, these setting effect a picture’s exposure. Getting a picture that displays the subject is of course key, but so is the exposure to get a good quality image of the subject.
Depending on the light available the ISO will change. The more light the lower the ISO needs to be set. For example a picture in broad day light would be fine with an ISO of 100. In contrast, a picture at night or in a dark room would demand an ISO of over a thousand. With higher ISOs the film grain/noise will become much more noticeable.
Aperture refers to the size of the whole of the lens which affects the amount of light that is allowed in. It is representative by the term f-stop (focal ratio). The larger the aperture the smaller the f-stop. For example an aperture that reaches maximum size with probably represented as a f-stop of 4. The larger the aperture (the lower the f-stop) the more light it lets in. Keeping this into consideration when compensating for exposure. Aperture also has the unique ability the either blur the background (if properly done) or making all details of the image equally clear. The higher the apeture (the lower the F-stop) will create an effect where the subject can be clear, while background is blurred. The lower the apeture (The higher the f stop) will allow all part of an image to be clear.
Referring to how long the shutter closes, the shutter speed is the final point when reaching optimal exposure. Measure in seconds how quickly the shutter speed closes can have a variety of affects on the image. First and foremost shutter speed effects the amount of light that is available. SO the faster the shutter speed the less light it will be letting in, and vice versa for longer shutter speed. Therefore, on a very sunny setting shutter speed can be shortened to compensate for maybe a large aperture, or high ISO. THe shutter speed also effects the image with motion blur. FOr example trying to take that split second (By split second it can be 1/6000th of a second) even like a bird’s wing movement, requires a faster shutter speed. Also when free handing to avoid motion blur from camera movement a fast shutter speed maybe necessary. When motion blur is wanted to display the actual movement of a subject a slower shutter spped (letting in more light) can be used.