Camera+Function

toc Camera Parts & Mechanics

**The Basics**


The camera, in it's most basic form, is simply a light-tight box with a hole on one side. The drawing above illustrates a concept observed over 1000 years ago in which light rays pass through a tiny hole in the "dark chamber" and invert the image from top to bottom and left to right. The process of photography, meaning "to write with light," wasn't invented until the early 1800s when a few different processes were invented to actually record the light entering the camera. Over time, the camera and the means by which to record light, has been reinvented many times over.

Modern cameras have a lens with an aperture and a body with a shutter, which can be used in combination to control the light entering the camera. Inside the camera is a light sensitive surface, usually film or a digital sensor, providing a way to record the light entering the camera. The three main functions of a camera are to view what is in the picture, focus to get a sharp image, and expose the film or sensor so the picture is neither too light nor too dark.

The type of camera we use in this class is called an **SLR**, or **Single Lens Reflex**, also **DSLR**, or **Digital SLR**. This type of camera allows the operator to look through the **viewfinder** (8) and directly through the **lens** (1) via a **pentaprism** (7) and a **mirror** (2). The image is focused on the **focusing screen**(5), which is the same distance to the **focal plane** (3). When the operator presses the shutter release button, the **mirror** swings, or "reflexes" up to expose the **sensor** (4) to light. Through this process, the **sensor** records the light transmitted through the **lens**.

This type of mechanism is unique to the **SLR**. The **rangefinder** camera has a separate window to look out of, so what the photographer sees and what the lens "sees" might not be exactly the same. A **TLR**, or **Twin Lens Reflex**, uses two lenses in conjunction to view and focus the light on the focal plane.

The above picture of Julia Roberts is cool for three reasons. First of all she is Julia Roberts. Second of all, she's using a Leica, one of the nicest (and most expensive) manually operated rangefinders ever made. The third reason this picture of Ms. Roberts is so cool is because she is holding her camera properly. If you want to look like you know something about photography, hold your camera like she does. Your right hand holds the camera body with your right pointer finger on the shutter release button. Your left hand supports the camera from underneath and focuses the lens simultaneously. By the way, Leicas are made in Germany.

Parts
It is important to learn the various parts of our DSLRs so that we have a unified vocabulary. Instead of saying, "The shiny round thingy," let's learn the real names for the parts of the camera. The following parts are necessary to know for manual operation.





Mechanics
The **shutter** is a curtain that opens and closes within the camera body, similar to a window curtain. The longer the **shutter** is open, the more light reaches the **film** or **digital sensor**. **Shutter Speed** represents the time that the shutter remains open when taking a photograph. Very fast shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Very slow shutter speeds are used to intentionally blur a moving subject for artistic effect. Measured in fractions of a second, the standard shutter speeds look like this: **1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1,** and **bulb**. With this scale, each increment roughly doubles the amount of light (longer time) or halves it (shorter time). For example, a shutter speed at 1/500th of a second is half the amount of light as 1/250th. For longer exposure times, it is good to know that the **"** mark stands for seconds. For example, if you set the shutter speed to **15"**, the shutter will remain open for 15 seconds. This setting may be good for extremely low lighting situations or occasions where you would like to see movement in the image on purpose. With your shutter speed set to **bulb**, the shutter will remain open as long as your finger is depressing the shutter release button.

The **Aperture** is the opening in the lens. Think of it like the iris of an eye. In bright situations, the iris closes down so as to not let in so much light. In dark situations, the opposite is true. The **aperture** is measured in **f-stops**. This is where it gets confusing, because f/2 would be a large aperture, while f/16 is a small aperture. So, the larger the **f-stop**, the smaller the **aperture**. As with shutter speeds, each increment you see below doubles the amount of light (larger opening) or halves it (smaller opening). For example, f/4 lets in half the amount of light as f/2.8.

As I explained above, the smaller the **f-stop**, the larger the **aperture**. This seems counterintuitive, but can be explained with a little simple math: **f-stop = focal length / aperture diameter.** The focal length and aperture are measured in millimeters. We are using cameras where the focal plane (where the digital sensor sits) is 50mm away from where the lens attaches to the camera, so the focal length is 50mm. A small aperture diameter might be only 3mm wide. Expressed mathematically: 50mm / 3mm = 16.666 Therefore, an aperture that is approximately 3mm wide indicates an f/16 for the f-stop. A relatively large aperture might be 25mm wide. Expressed mathematically: 50mm / 25mm = 2 (or f/2). This explains why a large f-stop = a small aperture, meanwhile a small f/stop = a large aperture.



Now we know how the **shutter speed** and the **aperture** work. Learning to use the two together forces the student to learn how the camera works and how to troubleshoot when problems arise. Using **Manual Mode** to adjust the **shutter speed** and **aperture** allows the operator to get the correct **exposure**, so that the image is neither too bright (overexposed), nor too dark (underexposed).

A good analogy for how the two work together is to consider a faucet filling up a bucket of water. If the goal is to fill up the bucket, we could open up the faucet for a very short time, but have a large opening, so a lot of water can come out. Or we could have the faucet open all day, but have only a tiny opening so that only a slow drip is able to flow. The goal of filling the bucket is equivalent to filling the sensor with enough light for a good exposure. We could open up the faucet for a very short time, or leave it open for days. Too little water = a dark photo. Too much water = a bright photo.

How do we know what senario to chose? Luckily, inside the camera is a light meter that reads the amount of light coming in through the lens. This information can be seen when looking through the viewfinder and also in the LCD panel on the back of the camera. In the first image below, the **shutter speed** is set at 1/200th sec, the **aperture** is set at f/2, and the light meter is telling us that the **exposure** is two **stops** too bright. The second image reads one **stop** too dark. The settings in the third image shows that the lighting //should// be neither too light nor too dark.

Film is coated with a light sensative crystals. **ISO** is a rating system that measures a film's sensativity to light. Some films have a low **ISO** rating and are better for outside shooting, while other films have a high **ISO** rating and can be used for dark situations. The idea of **ISO** has also been applied to digital camera sensors. We can set up the camera so that the sensor is very sensitive to light; so that a little light has a big effect on the sensor. Or we can force the sensor to be not so sensitive to light; so that in really bright situations, the sensor is not overloaded with light.

In our faucet analogy, changing the **ISO** would be like changing the size of the bucket. We could have a large bucket, in which case it would require a lot of water to fill it up. Or we could have a small bucket that could fill up in a relatively short time. The range of **ISO** settings normally look like this: **100, 200, 400, 800, 1600, 3200, 6400**. ISO 100 is used in bright situations and is not so sensitive to light. ISO 6400 is used in dark situations and is very sensitive to light. The higher the ISO, the more noise you will see in your photographs. A good place to start is to keep your camera set at ISO 400 and adjust from there if needed.