Have you ever checked what speed or what ISO your film is set at? Do you know how fast your stock is, and do you set the exposure accordingly?

If you want to get spectacularly clear pictures like those of professional photographers, then its time that you get sensitive to the film speed that you use while you are on a clicking spree. Film speed is measured in ISO or ASA or DIN. ISO is the internationally recommended standard of film speed and it combines the film speed in ASA along with DIN. It is necessary to know how your film speed or film sensitivity affects your photograph, before you chose one. Film speed or ISO defines the sentivity of your film, hence affecting the exposure time required. A film with a higher speed is more sensitive and requires less time for exposure.

For an analogue SLR camera, if you wish to change the sensitivity of your film then you will have to use a fast stock or a film with high speed, but in case of a digital camera you can easily go to the menu and set the ISO speed that you want. An ISO speed of 100 would require more exposure time or a slower shutter speed to reach the film’s threshold sentivity of 200 ISO.

The benefit of ISO speed is that it helps you to manipulate your exposure in cases where you can’t afford to change the aperture because you don’t want to affect the depth of field. Film speed helps you to attaint the same light at the same shutter speed which you would have got by going one stop above or below. So if you are facing low light at f stop 5.8 and shutter speed 1/125 and ISO 100, then you can achieve the right exposure by increasing the ISO to 200 and keeping the aperture and shutter settings same.