Photography Lesson: The Camera Body

The camera body is the main part of the camera. Basically, it contains the metering system, the viewfinder system, the shutter, the shutter controls, the shutter release button, and in most models, the built-in flash.  In film-based cameras, it has the film receptacle, the film spool, film advance lever, film release, and the ISO/ASA indicator switch. In digital cameras, it houses the electronics and exposure controls, the removable memory card interface, battery, image viewer, interface ports, and the electronic sensor.  Except for the SLRs and Medium-format cameras, the lens and aperture is permanently affixed to the body. 

Basic parts of a rangefinder camera

Parts of a typical SLR

Regardless of the design, the body has one overriding requirement: it has to be light-proof.  A small seepage will ruin an otherwise perfect picture.   In the case of underwater cameras, an obvious additional requirement is that it should be waterproof as well.  Some camera models are built as reusable waterproof cameras.  Most models would require an external waterproof shell to encase the regular (non-waterproof) body (and lens) to make it operate underwater.

We’ve already discussed the viewfinder systems in most of the camera designs so we won’t be discussing that in this section.  The following items discussed will familiarize you with the different controls found on the camera body.  Where applicable, we will distinguish which are found in manual film-based cameras and those found in digital cameras.  Indepth discussion about using the various controls will be found in succeeding lessons.

The Shutter

shutter is a device that allows light to pass for a determined period of time, either exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene.   In the early days of photography, the shutter was found in the front of the lens.  In modern cameras, the shutter is either just behind the lens, or just in front of the film or electronic light sensor (for digital cameras).

There are two basic types of camera shutter:  mechanical shutters and electronic shutter.

Electronic Shutters

Electronic shutters can turn each pixel on/off simulating the shutter speed.  This is more expensive  and is available on CMOS (Complementary Metal Oxide Semiconductor) sensors only.  CCD (Charge Coupled Diode) sensors still require a mechanical shutter to block off the light while the image is shifted out from the sensor to internal memory (jsut like a bucket brigade).

Mechanical Shutters

There are two basic types of mechanical shutters: the focal-plane shutters, and the leaf shutters.  Each are discussed separately.

  • Focal-plane shutters are usually implemented as a pair of cloth, metal, or plastic curtains which shield the film from light. The curtain partitions opens and closes (not at the same time; one after another) after the correct exposure time. Since these are located inside the camera body (just in front of the film (or digital image sensor) they allow the use of interchangeable lenses without requiring the expense of a separate shutter for each lens.  The down side is that since the curtains don’t open at the same time, fast moving objects get distorted.  Also, the mechanical structure is noisy (not good for candid or clandestined photography), results in camera shake, and has a limited life-span.
  • A leaf shutter is a type of camera shutter consisting of a mechanism with one or more pivoting metal leaves which normally does not allow light through the lens onto the film, but which when triggered opens the shutter by moving the leaves to uncover the lens for the required time to make an exposure, then shuts. Simple leaf shutters typically have only one shutter speed and are commonly found in disposable cameras. Some have more than one speed. Shutters for newer digital cameras are a combination of electronic and mechanical timings. Some cameras employ a 100% electronic shutter, created by turning on and off the imaging sensor’s signals. Digital cameras that can also take video implement this method for their video modes. For single-frame photography then either mechanical or mechanical+electronic methods are used.
Below, you’ll see each one in action.
 

Focal plane shutters open a segment at a time

Leaf shutters swivel leaves to permit exposure

Now that you’re familiar with how camera shutters operate, there’s just a couple more things you need to learn:

  • Shutter lag is the time between pressing the shutter release and the camera responding by taking the picture. While this delay was insignificant on most film cameras and some digital cameras, it may be a problem when trying to capture fast-moving subjects (e.g. sports cars, martial arts, tennis, etc.). Today, release shutter delay might be not an issue anymore. This is because the release lag has progressively diminished.  Release lag of Bridge camera Pentax X90 is only approximately 0.021 second.
  • A shutter cycle is the process of the shutter opening, closing, and resetting to where it is ready to open again. The life-expectancy of a mechanical shutter is often expressed as a number of shutter cycles.

Shutter Speed Selector

Settings on a typical shutter speed selector

This switch is found only in cameras that allow manual settings (e.g. SLRs).  It sets the shutter speed for the next shot, and succeeding shots until it is changed. The white colored range (2-1000) reflects fractions of a second (i.e. 2 = 1/2, 4 = 1/4, 60 = 1/60, and 1000 = 1/1000 of a second).   The orange colored range (1 – 8) indicate the time in seconds.  In this example, the shutter speed can be set at 1 second, 2 seconds, 4 seconds and 8 seconds.

An AUTO setting lets the camera decide based on the ISO (ASA for film-based) setting, aperture, and lighting conditions.

The B setting, or Bulb mode, will open the shutter as long as the photographer presses down on the shutter release button.  This can be useful in astrophotography (taking pictures of stars, planets, etc.).  However, you need to have the camera on a tripod, and using a cable release or remote control.

We’ll discuss the effect of shutter speed in taking pictures in the next lesson.

Film Speed (ASA)/Electronic Sensor (ISO) Selector

This control is found only in film-based cameras. Digital cameras have a similar control: it’s called the ISO setting.  Film speed control allows you to calibrate your camera’s meter to your film speed so that you will get an accurate exposure reading.  The film speed may be set electronically through a menu or via a knob/button on manual cameras. On film-based cameras, it is critical to set the proper value based on the ASA/ISO rating of the film loaded.  Not doing so will affect the exposure of images captured.

On manual cameras, the control is often integrated with a film speed indicator on the top of the camera (see figure below, left). On automatic cameras, the control and film speed indicator are generally separate with the film speed being indicated on the electronic menu display on the back of the camera.

Combination shuter speed & film speed knob

 

ISO Setting Screen (Pentax K-x)

We will discuss the effect of film sensitivity (ASA) or sensor sensitivity (ISO) in one of the succeeding lessons.

Metering/Flash Compensation

The cameras metering system is in the screen that you see through the viewfinder when composing a shot. It will measure the light settings of the scene.  In manual cameras, they provide a guide for you to set the ASA/ISO, shutter speed, white balance, and aperture so that you can expose the image correctly. In AUTO mode it sets the cameras shutter/aperture accordingly.

There are three basic metering modes: 

  1. Full mode means the camera will expose to the whole scene
  2. Partial mode means a part of the scene is measured (normally centre weighted)
  3. Spot metering will use the value from a single point.

Viewfinder display indicates at 1/250 sec f/8 the picture is underexposed

 

Pentax K1000 viewfinder (meter on the right)

The preceding picture shows a sample of an in-camera meter (left, digital display).  Different camera models have different representations. My very old Pentax K-1000 is a totally manual film-based camera (see image above, right).  The light meter is a stick (similar to a car’s fuel gauge) you can see on the right side of the screen (see figure above, right) –all you had to do was select the aperture and shutter speed to keep the needle in the center.  We will discuss metering in detail in one of the succeeding lessons.

F-Stop Control/Aperture Ring

Aperture & Focus Rings

On automatic cameras, the F-Stop control is on the camera. For manual cameras, the F-Stop is controlled on the lens. The F-Stop controls allow you to set the size of the aperture within the lens.  The aperture control the amount of light entering the camera, and also affects depth-of-field. 

Since this is found adjacent to the focus ring, you might get confused which is which.  The aperture ring normally has values with decimal points (in the example to the left, the values are 1.4, 2, 2.8, 4, 5.6, 8, 11, and 16.  Some lens have higher values.

The aperture functions like the iris nad pupil of the eye.  Depth-of-field is essentially how deep of the objects in the pictures are in focus (will be discussed in a succeeding lesson). 

Focus Ring

This is normally adjacent to the aperture ring.  To distinguish the focus ring from the aperture ring, the numbers on the aperture ring has decimal numbers, and the focus ring has 2 rows of numbers.  One row reflects the distance in feet, the other in meters (see figure above).

Film Compartment

In film cameras, there is a compartment in the back of the camera to hold the film. This compartment has a space for the film canister, sprockets to guide the film across the exposure area, a pressure plate to tighten the film, and a take up reel to wind the film. When the roll of film has been completely exposed, automatic cameras use a small motor to rewind the film (or a button on the bottom of the camera that allows you to rewind the film). Manual cameras require the photographer to turn a small “rewind knob” to manually rewind the film into the canister. If the film is not rewound before the back compartment is opened, the film will be exposed, thus ruining the images.

 12. Film rewind knob, 13. Film rewind crank,  25. Viewfinder eyepiece, 26. Film pressure plate, 27. Guide pin channel, 
28. Winder/Motor Drive direct contact terminal, 29. Film chamber,  30. Battery chamber,  31. Motor Drive/Tripod receptacle 
32. Film rail,
33. Film guide rail,  34. Shutter curtains,  35. Film rewind button, 36. Film transport coupler, 37. Bulk magazine guide pin channel, 38. Sprockets, 39. Film take-up spool,  40. Back cover

Flash

Most cameras now include a built-in flash. Some are simple light bulbs built into the front of the camera. On SLR cameras, most built-in flashes pop-up out of a protective storage area on the top of the camera. External flashes can often be attached via the “hot shoe mount” or, in the case of manual cameras, an small connector port on the front of the camera that accepts a cable attached to a distant flash.

Built-in Flash (Pop-up)

 

Built-in flash (fixed)

 

Hotshoe Connection

Hot Shoe Mount

The hot shoe mount is a point on the top of most SLR cameras where an external flash can be connected. It is called a “hot shoe” because it has electrical contact points and guide rails that fit over the bottom of the flash like a shoe.

Lens Ring Mount

Lens Mount

On cameras that allow interchangeable lenses, there is a metal ring on the front of the camera where the lens will attach. This ring contains electrical contact points to connect the lens controls to the camera body. There is a small button or lever to the side of this mount called the “lens release button” that releases the lens from the body.  To attach the lens, you need to align the orange dot on the lens to the corresponding one on the lens mount.

There are two (2) basic lens mount: screw-threaded type, and bayonet type.  The screw type, as the name implies, the inside edge has grooves, and the lens have the corresponding thread pitch.  To simplify things, the mechanism is like a nut and bolt.  The lens mount is the nut (with the grooves), and the lens is the bolt (with the threads).  The bayonet type, also known as friction-lock type, features tabs on the inner edge of the lens mount (see figure on the left), that match the tabs on the edges on the tail-end of the lens.  Different camera brands have different dimensions for the bayonet type lens mount making lens incompatible.

Note that interchangeable lens don’t fit all camera brands.  3rd party lens manufacturers (e.g. Tamron, Tokina, Sigma, etc.) manufacture lens specific to a lens mount type. If intend to buy additional lens for your SLR/DSLR, make sure that the lens matches your camera’s brand and model.  For example, I bought a 28-200mm Tokina lens for my old Pentax K-1000 15 years ago.  Before I decided to buy a DSLR, I wanted my old lens to work on the new DSLR body. It’s great because my old Tokina works well with my new Pentax K-x DSLR (except for Auto-Focus)–I’m perfectly comfortable with using manual focus anyway. I won’t discuss the different exposure settings found in digital cameras in this section, those deserve their own sections.

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