Sunday, 22 January 2017

Relation between ISO, shutter speed, aperture and light in photography

Photography is a word having Greek roots, which basically means "drawing with light". When I started doing digital photography few years ago, this did not make sense to me at all. How can you make a picture just using light? Only light matters? My pictures were blue, black, red and washed out all the time, but I didn't feel like giving up. It took me a fair amount of time to understand controls such as shutter speed, aperture and ISO which was the outcome of non-stop reading and a lot of mistakes.

pin hole camera
Pin hole film camera
Coming back to the concept of light, it started to make sense when I attended a film photography workshop couple of years ago. The dark room with very dim or near to zero red lights was a whole new point of interest for me. My partner and I made a pin hole camera out of Pumpkin. Here is an image of our pinhole camera, sorry for making my pumpkin look upset. ;)
The workshop made me understand how important light is when taking pictures, and the rules apply to both film and digital photography. Basically the value of ISO, Shutter speed and Aperture directly affect the amount of light hitting the sensor. This light gets transformed into an image by sensor circuitry. A short and crisp way of explaining the light variation whenever one of these values is changed is shown in the image below.

ISO, Shutter speed and Aperture effect on light
Effect of ISO, Aperture and shutter speed on amount of light

The tricky part here to understand here is how to vary each of the above three things simultaneously. A couple of quick examples:
1) Sunset landscape shot: Low shutter speed for more light, high f-stop for more details. Yes, high f0stop would minimize the light, but shutter speed would cover up for it.
2) Bike racer daytime action: Fast shutter speed to freeze action. F stop as low as possible to make background out of focus. If image is blow out(too white), then only solution is to increase f stop so as to control the incoming light.
Quick tip: When to vary ISO? Well, depends on the situation. Example: A dancer inside a low light room. If the lowest feasible shutter speed (to freeze action) and lowest f stop are not able to provide properly exposed shot (hard to see dancer's face), then ISO becomes a life saver.

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