Cameras and Exposure

Cameras and Exposure

As we learned with our pinholes, every camera is just a lightproof box with a method of letting in an amount of light for just the right amount of time. This "right amount of time" gives us a good exposure for our image. Light Bulb, Abelardo Morell

When light is let inside a camera, it forms an image made of light Light Bulb, Abelardo Morell

And when this image made of light reaches a light sensitive surface inside the camera the image is recorded as an exposure.

In a pinhole camera or film camera, photographic paper or film which is covered with a light-sensitive emulsion containing silver halide crystals, captures onto its surface the light that is projected into the camera forming a latent image that we then develop with chemicals.

The chemical development then converts the film s exposed silver halides into black particles of metallic silver, making this latent image become visible as a negative image.

This negative image can then be used to make positive prints in the darkroom. negative positive print

Rather than chemically, digital photography responds electronically to light and captures an image onto a digital sensor. The sensor is a layer of silicon covered with a grid of light sensitive cells called photosites.

How it works is that each photosite collects and measures the amount of light that reaches it during an exposure. It measures the light by giving it a numerical value of between 0 and 255 which relates to a make up of three color channels: R, G & B (the 3 colors that make up white light).

After each exposure, the photosite s measurements are converted into code by the camera s circuit board & stored on the camera s memory card. Then the sensor clears like an etch-a-sketch & is ready to read the next exposure.

The readings recorded from each photosite during an exposure are individually known as picture elements: these picture elements are what we call Pixels.

Hundreds & thousands of pixels, each made up of a single value and color, make up a digital image all placed together in a grid, like a mosaic or a drawing on graph paper.

This grid is recorded to your camera's memory card & then transferred to your computer where it is reassembled on the monitor so you can view, edit and print your image. Boom.

IMAGE QUALITY controls the number of pixels per inch that make up your image the lower the image quality, the less pixels per inch, the choppier the image will look (will not work as a print!); the higher the image quality, the more pixels per inch, the awesomer the image will look (will work as a print!) always choose highest image quality (gives you more options later) low quality high quality

IMAGE QUALITY low quality high quality

IMAGE QUALITY often called File Size in your camera menu

Exposure in a digital camera

Since exposures are dependant on the amount of light that reaches the light sensitive element inside a camera, cameras are built with a few key parts that allow you to control just how much light gets in, how long the light gets in for, and how sensitive the sensor is to that light. These guys are: APERTURE (F STOP) determines how much light enters the camera at a time SHUTTER SPEED controls the amount of time that this light is let into the camera for ISO controls how sensitive the digital sensor is to this light; how receptive it is to recording it

Aperture (f stop) controls the size of the hole (lens opening) that lets light into the camera (it's like your pinhole) determines the amount of light that enters the camera at one time measured as f-stops: f1.4, f2.8, f4, f5.6, f8, f11, f16, f22... f/1.4

Aperture (f stop) the larger the opening (but the smaller the number!), the more light comes into the camera; the smaller the opening (but the larger the number!), the less light comes into the camera.

Shutter speed controls the amount of time that this light is let into the camera for (it's like your black tape!) measured in seconds and fractions of a second: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000...

Shutter speed the faster the shutter speed (the smaller the fraction of a second), the less light comes into the camera; the slower the shutter speed (whole numbers or larger fractions of a second), the more light comes into the camera.

ISO controls the digital sensor's sensitivity to this light determines how receptive the sensor is to recording the light the lower the #, the less sensitive it is to light; the higher the #, the more sensitive it is to light: least sensitive 80, 100, 200, 400, 800, 1600, 3200 most sensitive bright light dim light

aperture + shutter speed + iso = exposure!

aperture + shutter speed + iso = exposure! iso aperture shutter speed They work together! And determining the right combination of the 3 of them will give you a good exposure for each photograph that you make.

Your cameras have a built in through-the-lens light meter or exposure meter that measures the amount of light (aperture + shutter speed + iso combination) necessary to get a good exposure for the particular lighting conditions at hand. exposure meter aperture shutter speed iso

reading an exposure meter

exposure test in an overall lighting situation under exposed: loss of shadow details dark flat/lacks contrast good exposure: details in shadows & highlights most dimension good range of tones over exposed: loss of highlight details very light extreme contrast

exposure test in an uneven lighting situation under exposed: loss of shadow details dark good exposure: details in shadows & highlights over exposed: loss of highlight details very light Although the middle exposure seems perfect to some us, someone may want more drama in the image and prefer the underexposed image on the left.

one other thing

One other new thing to think about is that even though we don't always see it, light has different color temperatures. These temperatures are measured using the Kelvin Scale. The lower the temperature, the more yellow and red are found in the light and the higher the temperature, the bluer the light will look.

Your camera has several white balance settings to make up for the different color casts of the light you re shooting in.

These settings allow your camera to measure the temperature of light you re shooting in & to balance out the colors of your photograph by compensating for its temperature and removing unrealistic color casts. unrealistic color casts good white balance

Most of the time, the auto mode will do a pretty good job of detecting the type of light you are shooting in and compensating for its color, but if your image looks too blue, too yellow, or just weird, other options are there for you to try out.

Having the correct white balance is major part of having a good exposure, so always check how your images are coming out color-wise as you go. Color casts can really make or break a photo.

You want the viewer to notice your composition and not just be distracted by crazy banana pants color casts.

getting started

With a digital camera, there s a tricky balance between wanting to know everything your camera can do & knowing only what you need to in order to get good exposures at the right file size.

This means that most of the camera s features are things that you really don t need to concern yourself with. All you need to know for now is how to access the camera controls that will allow you to take good exposures by using the exposure meter, at the right file size and correct white balance setting. mode dial: how you get to manual setting if possible so you can change your aperture and shutter speed and use the exposure meter to get a good exposure. ISO setting: how you change your camera's sensitivity to light control dial: how most of you will access your camera's settings to choose your file-size setting & white balance setting

file size (image quality) largest/superfine white balance setting start at auto, if things look weird, adjust shooting mode manual and then use exposure meter iso stay between 100 800, start at 100 & move upwards is needed aperture & shutter speed what you'll adjust for each shot to balance out your exposure meter

Also, always set your lens to manual focus