Exposure2

This is the oft-referred to "exposure triangle" used to show ISO, Shutter-Speed and Aperture.



Let's go back to the waterfall photograph, here's how I set my exposure.

First, I set the lowest ISO I can. I want an ISO that is not at all sensitive to light because my intention will be to starve my exposure of light, so I want to do everything I can to do that. 

It will be ISO 100, something at the low end of sensitivity and also grain/noise. (A bonus!)

Next, I will choose the property that gives me the greatest value.

With a waterfall though, I will select the Shutter-Speed, probably starting at 1/2 of a second.

Now I set the Aperture to whatever will bring my light-meter into balance.

me

Take a good look at ALL the examples in this slideshow.

While each image has the same balanced exposure, they all LOOK different.

In this case, it's the water that has the most impact.

The ISO is unchanged (at ISO 200), but what does change is the Shutter-Speed and the Aperture. If I were to change the Shutter-Speed (so it stays open longer to blur the water), I must close the Aperture down in equal proportion.

Conversely, if I wanted a fast Shutter-Speed to freeze the water, I must open up the Aperture to allow more light to pass through the lens.

If I were to open up the Shutter-Speed without adjusting the Aperture to match, I end up with an image that is lighter.

When shooting on film, we will not know whether we achieved a good quality image or not, until it gets developed. That's just how it is.With digital though, most cameras (and apps) will have something called a histogram and without a doubt, this is your best friend for determining image quality.

The histogram is a graph that shows how the image stacks up, literally.

A digital camera's LCD display allows for instant feedback of our photos, that's all.

NEVER trust it to determine if the exposure is good or not.

Instead, use the camera's Histogram display.

The brightness value of each pixel is measured, organized and stacked one-upon-another.

The graph it creates goes horizontally across the bottom, from left (black) to right (white) and covers the entire tonal range in-between.

Pixels are stacked vertically, and the more pixels there are at any given point, the taller the graph. Our aim is for a balanced exposure, something resembling a mountain range, where the pixels are concentrated in the middle of the graph.

Much like what is seen in this graphic.

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