Using your digital camera, frame a well-lit scene with the following settings:

set the shutter speed to 1/50 and the aperture to f/8. take the picture.
if the photograph is too dark or too light, change the shutter speed until the image has realistic lighting.
now change the iso while keeping the other settings unchanged. observe the results.

(Answers may vary.)

Initial shutter speed: 1/50 second

Initial aperture: f/8

Result: Dark/light image

Shutter speed: 1/30 second (if the original image is dark)

Aperture: f/8

Result: A lighter image

Shutter speed: 1/80 second (if the original image is light)

Aperture: f/8

Result: A darker image

Initial shutter speed: 1/50 second

Initial aperture: f/8

Result: Dark/light image

ISO: 400, 200, 100  (if the earlier image is overexposed)

ISO: 100, 200, 400(if the earlier image is underexposed)

Explanation:

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