Who has the best description of how ISO (the sensor), shutter speed, and aperture work?

Started Jan 24, 2014 | Discussions thread
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GBJ Regular Member • Posts: 243
Who has the best description of how ISO (the sensor), shutter speed, and aperture work?

I'm curious about the most effective way to describe the relationship of the factors which a camera uses to make a photograph. Essentially, how do you describe the way the camera uses ISO, shutter speed, and aperture, to achieve the correct exposure?

I've explained it before to members in my photography group, by using the comparison of water and plumbing, to photography, but I'm curious what is the most detailed and effective way to describe and have someone understand the camera's sensitivity to light through iSO...etc.

How would I describe this to a new photographer, someone who is very intelligent...but remember, they know nothing about cameras, and have no previous terminology, so assume they will not know what you are talking about unless you use clear, unassuming language.

Hey, if you are not interested in teaching others about this topic, then I understand if you don't feel you need to reply to this post.

I have, in the past, explained exposure being like a clear drinking glass. The glass is the photograph, and when the glass is filled with water, it has been properly exposed. When it is underfilled, it is underexposed. When it is overfilled, it is overexposed. Water flows into the glass through a hose, and you can either use a hose that is small, like the size of a straw, or use a hose that is larger, like the size a garden hose. The diameter of these hoses, can be compared to the diameter of the hole in the lens of a camera, through which the light enters the camera. The hole in the lens can be made larger, or smaller, in order to let more, or less light into the camera. The size of the hole in the lens is referred to as aperture.

The larger the diameter of the hose, the more quickly the glass of water will fill to the top.

The smaller the diameter of the hose, the slower it is to fill the cup, given that the water pressure is the same as when using the larger diameter hose. So knowing this, we need to stop the flow of water into the cup, at different durations of time, so the cup does not overflow.This is similar to the camera, and how it uses the speed of the shutter to stop the light within the lens from entering the camera and striking the sensor. It uses the speed of the shutter to prevent the photograph from being overexposed, or underexposed.

The camera uses a rectangular shaped surface, called the sensor, to collect light, and form a photograph. Light enters the lens, passes by the shutter when it is open, then strikes the surface of the sensor. Pretend that the sensor has the characteristics of a white piece of paper. If the paper is super thin like a tissue, if you use a magnifying glass to reflect the rays onto it's surface, it will burn very quickly, because it is very sensitive to the effect of light.

On the other hand, if the paper is not thin, but is a thick piece of white paper, then reflecting the sun on to it will take a longer duration of time to burn, because it is less sensitive to the effect of light.

The ISO is the measurement of the sensor's sensitivity to light. At iso 100, the sensor is not very sensitive to light, like the thick piece of white paper. As you raise the iso, say to iso 1000, the sensor is much more sensitive to light, like the tissue paper.

I guess we can also compare the camera's iso sensitivity to the glass, as mentioned above, but in this case, there many iso glasses. Iso 100 glass is a large size glass. Iso 500 glass is a medium size glass. Iso 1000 glass is a small size glass. The small size glass will fill with water to it's top, achieving proper exposure, more quickly than the large size cup, given that the flow of water is equivalent. In the camera, this means that setting a higher iso level will allow for a faster shutter speed...we can cut the flow of water off more quickly so that the water doesn't overflow and run down the side of the glass.

The force of the water pressure through the hose, is like the intensity of the sun entering the lens.

Anyways, all this is not totally clear, but I'm wondering how this forum of experienced photographers would direct their way of seeing this. I'm hoping that it will be fun for other people to contribute their view to this forum...perhaps a new post from first time writers, if you feel like it?

Thanks for your input.

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