Dan Kang

Introduction to Photography: Exposure

SF apartment

I purchased a DSLR earlier this week, and I’ve been having a blast with it as you can see by all the pictures I’ve been taking around San Francisco.

Since I am a baby photographer, I’m learning all the basics and figured it would be a good idea to jot down the important bits that I learn so that I can teach myself in my own voice when I need a refresher. If you see anything off or just flat out wrong, I’d love to know.

Every “introduction to photography” article that I’ve found through the Googles starts by going over exposure. Exposure is how much the light gets through to the image sensor, which is the component of the camera that converts light into the electrical signals that make up the photograph. Basically, exposure determines how bright or how dark your photograph is.

When thinking about exposure, you need to keep three major factors in mind: aperture, shutter speed, and ISO sensitivity.

Aperture

The aperture is the hole that the light passes through right after going through the lens. You can adjust how large or small the opening is, and that in turn will let in more or less light. It’s expressed as an “f-number” such as f/4, f/5.6, f/8, etc. The important thing to keep in mind is that the higher the f-number (e.g. f/32), the smaller the aperture, which means that less light will get through. The lower the f-number (e.g f/1.4), the larger the aperture, which means more light will get through.

Aperture also determines depth of field, which is how much distance in front of and behind the focus point appears to be in focus. A small aperture (high f-number) will produce a long depth of field which will make most of your photograph appear to be in focus. This is great for landscape shots. A high aperture (low f-number) will produce a short depth of field which will make parts of the photograph outside of the focus point appear out of focus. This is great for producing a blurry background when you’re taking a portrait shot.

Shutter speed

Unlike aperture with its fancy f-numbers, shutter speed is expressed in seconds and is easy to understand. The shutter speed controls how long the shutter in front of the image sensor is kept open, which affects how much the image sensor is exposed to light. The slower the shutter speed (e.g. 1/6 of a second), the more light gets through. The faster the shutter speed (e.g. 1/250 of a second), the less light gets through. Pretty simple.

Shutter speed also controls how motion is captured in the photograph. If you have a fast shutter speed, any movement will be frozen in time. On the other hand, you might actually want to suggest a lot of movement using motion blur in which case you should use a slower shutter speed.

ISO sensitivity

ISO sensitivity measures how well the camera is able to capture light. ISO determines how much the electrical signals are amplified. Doubling ISO will double the electrical signals which means you’ll need half the light needed to get the same exposure. For example, if you need to double your shutter speed and want to keep the same aperture, you can double your ISO number to get the same exposure.

Be warned though, because a high ISO will add a lot of noise into your photograph which you don’t want. You want to use a higher ISO only when you need to in dark places and stick to lower ones otherwise.

Summary

Exposure is controlled by aperture, shutter speed, and ISO sensitivity.

Small aperture (high f-number) = less light + long depth of field Large aperture (low f-number) = more light + short depth of field

Faster shutter speed = less light + less movement Slower shutter speed = more light + more movement

Low ISO = less light + less noise High ISO = more light + more noise