Camera Design

Chapter Six

Pinhole camera

A pinhole camera is a very simple camera with no lens and a single very small aperture. Simply explained, it is a light-proof box with a small hole in one side .  Light from a scene passes  through this single point and project  an inverter image on  the opposite side of the box. Cameras using small aperture and the human eye in the bright light both  act like a pinhole camera.

The smaller the hole, the sharper the image, but the dimmer the projected image .Optimally the size of aperture should be 1/100 or less of distance between it and the screen.  A  pinhole camera’s shutter is usually manually operated because of the lengthy exposure times, and consists  Of a flap of some light-proof material to cover and uncover the pinhole .Typical exposure  range from 5 seconds to hours and sometime days.

A common use of the pinhole camera is to capture the movement of the sun over a long period of time. This type of photography is called Solargraphy . The image may be projected onto a translucent screen for real-time viewing (popular for observing solar eclipses), or can expose film or a charge coupled device (CCD). Pinhole cameras with CCDs are often used for surveillance because they are difficult to detect. 

Plate Camera

 

The earliest cameras produced in significant numbers used sensitized glass plates and are now termed plate cameras. Light entered a lens mounted on a lens board, which was separated from the plate by an extendible bellows. Many of these cameras, had controls to raise or lower the lens and to tilt it forwards or backwards to control perspective. Focusing of these plate cameras was by the use of a ground glass screen at the point of focus because lens design only allowed rather small aperture lenses, the i9mage on the ground glass screen was faint and most photographers had a dark cloth to cover their heads to allow focusing and composition to be carried out more easily. When focus and composition were  satisfactory , the ground glass screen was removed and a sensitized plate put in its place  protected by a dark slide (photography).to make the exposure , the dark slide carefully slid out and the shutter opened and then closed and the dark-slide  replaced. In current designs the plate camera is best represented by the view camera.

Large Format Camera

The large format camera is a direct successor of the  early  plate  cameras and remain in use for high quality photography and for technical, architectural and industrial photography. There are three common types, the monorail camera, the field camera and the press camera. All use large format sheets of film, although there are backs for medium format 120-film available for most system, and have an extensible bellows with the lens and shutter mounted on a lens plate at the front. These cameras have a wide range of movements allowing very close control of focus and perspective.

Medium Format Camera

The medium –format cameras have a film negative size somewhere in between the large format cameras and the smaller 35mm cameras. Typically   these system use 120- or 200 film. The most common sizes being 6x4.5 cm, 6x6cm and 6x7  cm. The designs   of this  kind of camera shows greater variation than their larger brethren. Ranging   from monorail  systems , via the classic Hasselblad model with separate backs, to smaller rangefinder cameras. There   are even compact amateur cameras available in this format.

Folding Camera  

The introduction of film enabled the existing designs for plat cameras to be made much smaller and for the base-plat to be hinged so that it could be folded up compressing the bellows. These designs were very compact and small models were dubbed Vest pocket cameras.

Box Camera

Box camera were introduced as a budget level camera and had few if any controls. The original box Brownie model had a small reflex viewfinder mounted on the top of the camera and had no aperture or focusing controls and just a simple shutter. Later models such as the Brownie 127 had a direct view optical viewfinder together with a curved film path to help.

Rangefinder Camera

As camera and lens technology developed and wide aperture lenses became more common range-finder cameras were introduced to make focusing more precise. The range finder had two separated viewfinder windows one of which was linked to the focusing mechanisms and moved right or left as the focusing ring was turned. The two separate images were brought together on a ground glass viewing screen. When vertical lines in the object being photographed met exactly in the combined image, the object was in focus. A normal composition viewfinder was also provided.

Single-Lens Reflex (SLR) 

In the single-lens reflex camera the photographer see the scene through the camera lens. This avoids the problem of parallax, which occurs when the viewfinder or viewing lens is separated from the taking lens. Single-lens reflex cameras have been made in several formats  including 200/120 taking 8, 12 or 16 photographs on a 120 roll and twice that number  of a 200 ISO or film. These correspond to 6x9, 6x6 and 6x4.5 respectively (all dimensions in cm). Notable manufactures of large format SLR include Hasselblad, Mamiya, Bronica and Pentax. However the most common format of SLRs has been 35mm and subsequently the migration to digital SLRs, using almost identical sized bodies and sometimes using the same lens system.

Almost all SLR used a front surfaced mirror in the optical path to direct the light from the lens via a viewing screen and pentaprism to the  eyepiece .At the time of exposure the mirror flipped up out of the light  path before the shutter opened. Some early cameras experimented other methods of providing through the lens viewing including  the use of a semi transparent pellicle as in the Canon Pellix and others with a small periscope such as in the Corfield Periflex series.

Digital Single-Lens Reflex (DSLR)

A digital single lens reflex camera (digital SLR or DSLR ) is a digital camera that uses a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera. The basic operation of a DSLR is as follows: for viewing purpose , the mirror reflects the light coming through the attached lens upwards at a 90 degree angle. It is the reflected twice by the pentaprism, rectifying it for the photographer’s eye. During exposure , the mirror assembly swings upwards, the aperture narrows (if stopped down, or set smaller than wide open), and a shutter open, allowing the lens to project light onto the image sensor. A second shutter then covers the sensor, ending the exposure, and the mirror lowers while the shutter resets. The period that the mirror is flipped up is referred to as “viewfinder blackout”. A fast-acting mirror and shutter is preferred so as to not delay an action photo. All of this happens automatically over a period of milliseconds, with camers designed to do this 3-10 times a second.

 

DSLRs are often preferred by the professional still photographers because they  allow an accurate preview of framing close to the moment of exposure , and because DSLRs allows the user to choose from a variety of interchangeable lenses. Most DSLRs also have function that allows accurate preview of depth of field.

Twin-Lens Reflex (TLR)

Twin-lens reflex cameras used a pair of nearly identical lenses, one to from the image and one as a viewfinder. The lenses were arranged with the viewing lens immediately above the taking lens. The viewing lens projects an image onto a viewing screen which can be seen from above. Some manufacturers such as Mamiya also provided a reflex head to attach to the viewing screen to all the cameras to be held to the eye when in use. The advantage of a TLR was that it could be easily focused using the viewing screen and that under most circumstances the view seen in the viewing screen was identical to that recorded.

Some TLR had interchangeable lenses but as these had to be paired lenses they were relatively heavy and did not provide the range of focal lengths that the SLR or DSLR could support. Although most TLRs used 120 or Films some used 127 film (ISO ).

In next chapter we talk on  Photography Basic Techniques and Terminologies. If you have any question regarding  PHOTOGRAPHY   just feel free to ask . So stay with us and like us on facebook