Digital SLR Camera

ISO speed is the third element that “makes” a photo. It is usually expressed with the following numbers:

50 | 100 | 200 | 400 | 800 | 1600 | 3200These numbers tell you how “fast” does the digital sensor react to the light sent through the aperture and shutter.A small number means that it takes a relatively long time to take a photo, a large number, a very short time.But things are relative in using the right ISO setting. On an average digital camera, the ISO goes from 50 to 400.The ISO speed 50 is usually used on bright sunny days, while the 200 and 400 ISO is used in low light conditions (like interiors or at night)There is also a problem with the image quality regarding the ISO speed. At large numbers, 400, 800, the image will contain “noise”, so use the low ISO speed as much as possible.Here is a table that will further explain how the aperture, shutter speed and ISO speed are used TOGHETHER to “make” an image.I’ll give a theoretical example of how this three indicators work together: At ISO speed 100 you select an aperture of 8 and the shutter speed is calculated by the camera at 1/250 sec. The same image*, mathematically speaking, can be created using the following settings:

ISO speed	Aperture	Shutter speed
100	16	1/60
100	11	1/125
100	8	1/250
100	5.6	1/500
100	4	1/1000

same image* - the same in theory but with different effects on the final, real imageAs you can see, with the ISO speed constant, the aperture and exposure time increase or decrease in connection with each other; if the aperture allows more light into the camera, the shutter speed decreases to compensate and give the perfect exposure.But what happens to these theoretical numbers if you set the ISO speed at 50? Take a look:

ISO speed	Aperture	Shutter speed
50	11	1/60
50	8	1/125
50	5.6	1/250
50	4	1/500
50	2.8	1/1000

You can modify the aperture, keeping the shutter speed constant, or you can modify the shutter speed, while keeping the aperture values constant:

ISO speed	Aperture	Shutter speed
50	16	1/125
50	11	1/250
50	8	1/500
50	5.6	1/1000
50	4	1/1250

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