Course Name: Photography and Audio Visualproduction (Vocational) for Under Graduate (Firstyear)
COURSE NAME: PHOTOGRAPHY AND AUDIO VISUALPRODUCTION (VOCATIONAL) FOR UNDER GRADUATE (FIRSTYEAR)
PAPER TITLE: BASIC PHOTOGRAPHY
UNIT - 5: CAMERA CONTROLS - 1
TOPIC: LENS, APERTURE AND SHUTTER
OBJECTIVES
By the end of the session, students will be able to;
1. Understand the camera controls,
2. Understand the lens system,
3. Know the shutter control,
4. Understand the focus and zoom control,
5. Differentiate between exposure and shutter control.
6. Develop interest in creative photography using camera controls.
Introduction
In this lesson we will discuss the Essential Parts of a Camera like the Lens, Light Tight Chamber and View Finder and their controls. In that we will include Lens Controls that is controls with Focusing Ring, Aperture Ring, Zoom Ring and the Shutter Control that is with the help of Shutter Speed dial.
The Lens
Today lens is integral part of any camera. A lens can be fixed permanently in the camera body or there can be interchangeable lens. Lens is an optical device made of any transparent material bounded by two sides one of them must be a part of a sphere.
Camera Lens
Lens is responsible for forming the optical image. A camera lens has to be essentially a positive lens that forms a real inverted image when the object is at a distance of more than one focal length from it.
Light rays traveling from the object at infinity parallel to the principal axis of a lens after refraction either converge or appear to converge at a point on the principal axis. This point of convergence is known as the principal focus of the lens. The distance between the principal focus and the centre of the lens is known as focal length of the lens.
The lenses of different focal length can result remarkably different pictures of the same scene. It can influence the field of view and the magnification of the image.
The Horizontal Field of View
A lens can produce image of the objects covering certain area in front of it. Its coverage is spread over certain horizontal as well as vertical angle. In photography when we talk about the field of view of any lens we normally refer to its horizontal field of view. Accordingly to their horizontal field of view we can categorise lenses as normal, wide and telephoto lenses.
Normal Lens
A Normal Lens covers the angle, which is about the same, as the human eye would encompass, that is about 530. The focal length of normal lens is close to the diagonal of the format.
Here I would like to cite an example of Henri Cartier-Bresson, universally acknowledged as one of the most influential photographers of the 20th century. He described his first camera Leica bought in 1932, as "an extension of my eye" and was intended merely as an aid to his art.
He almost always used a normal lens. The angle of view of most of his images is about the same as what the eye can see clearly from one position, and the relative size of near and far objects seems normal.
Wide Angle Lens
A wide Angle Lens covers the angle more than the human eye would encompass, that is more than 530. The focal lengths of wide angle lenses are less than to the diagonal of the format.
Wide angle lenses tend to magnify the perceptible distance between objects while allowing greater depth of field in the image. Regarding this depth of field we will discourse in the next lesson.
Another result of using a wide-angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject: parallel lines converge at the same rate as with a normal lens, but converge more due to the wider total field.
For example, buildings appear to be falling backwards much more severely when the camera is pointed upward from ground level than they would if photographed with a normal lens at the same distance from the subject.
Further, Forced perspective of the wide angle lens often produces distorted image when the camera viewpoint is close to the object. They reproduce the foreground object appear too large with respect to the rest of the background objects.
Telephoto Lens
A telephoto Lens is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length.
A telephoto lens covers a smaller angle than a human eye would encompass, which is less than 530. The focal lengths of telephoto lenses are more than the diagonal of the format.
Telephoto lenses tend to compress the perceptible distance between objects and produce shallow depth of field in the image.
Prime/ Fixed Focal Length lenses
Lenses of fixed focal lengths are known as prime lenses. They have fixed angle of view. In some interchangeable lens cameras one can select lenses of different focal length to have desired angle of view.
Covering power of a lens
When a lens projects an image on the focal plane its sharpness and the brightness fall off steadily as it moves away from the axis of the lens. Covering power of a lens refer to the maximum area of focal plane over which the lens is capable of giving an evenly illuminated image of an acceptable standard of definition.
Because of this property a lens designed for bigger format can be used for smaller format cameras but not vice versa.
The Viewfinder
It is essential to know not only what direction to aim the camera but also how much area of the subject is included in the picture.
A viewfinder is what the photographer looks through to compose, and in many cases to focus, the picture. For this reason practically every camera is provided with a viewfinder. Different types of cameras like still, movie, film and digital use different kind of viewfinders.
Direct vision Optical Viewfinder
Direct vision Optical Viewfinders the viewer’s eye was placed at the back and the scene viewed through the viewfinder optics.
There was some parallax error as the viewfinder was offset from the lens axis; the view was seen from a point above and usually to one side of the lens. The error varied at different distances, being negligible for distant scenes, and very large for close-ups.
Twin Lens Reflex Viewfinder
Twin-lens reflex cameras use a separate lens of similar size and focal length above the taking lens, and a mirror is placed at 45° to project the image onto a ground glass screen viewable from above, with the camera at waist level. It also suffers from parallax error as the taking lens and the viewing lens is at different position.
Single Lens Reflex Viewfinder
Single-lens reflex cameras use the same lens for viewing and taking the picture and therefore it is free from any parallax error.
Inside the camera body there is a mirror placed at 45° to project the light passing through the lens and form the image on the ground glass placed at the equidistance from the focal plane. It had a mechanism which flipped the mirror out of the way when the shutter button was pressed, followed immediately by the shutter opening.
A roof pentaprism is used to allow erect viewing by holding the camera at the eye level. The big advantage of the Single-lens reflex cameras was that any lens, or other optical device, could be used; the viewfinder always showed exactly the same image that would be projected onto the film.
Digital Camera LCD Screen View Finder
Almost all digital cameras available in the market now have a LCD (Liquid Crystal Diode) viewfinder. It lets you see exactly what the finished digital image looks like. The LCD monitor works great in dim light condition compared to optical viewfinder and no parallax errors too!
However, many colour LCD monitors perform badly under bright sunlight. They also consume lot of power and if you are concerned with battery drain on your digital camera turn off the LCD whenever you don't need it.
Focusing Ring
You may locate three sets of ring to control the image formed by the lens. The outer ring is a Focusing ring. By turning this ring the photographer can controls the sharpness of the image. Focusing rings are usually marked both with foot and meter showing how far away a subject is when focused.
On an automatic camera, focusing ring is moved by a small motor placed within the lens system whenever the photographer presses the shutter release button halfway down.
By turning focusing ring the lens adjusts the image distance, object distance and at times even the focal length of the lens to satisfy the famous lens equation:
1/u + 1/v = 1/f.
[Where, u= object distance, v=image distance and f= focal length of the lens]
Focusing Aids
To facilitate easy focusing different focusing aids are used. Most common is Ground glass focusing screen.
Ground Glass
Ground glassfocusing screen is a flat translucent material, the framed image is allowed to project on the ground glass screen to facilitate preview as well for focusing. If needed the photographer take help of magnifying glass to judge the focus.
Split Image
In non-autofocus 35 mm SLR cameras is the split screen and micro prism ring aids focusing became standard since 1980s.
The split image wedge system allows highly accurate focusing. When out of focus the split screen split the image in two pieces. When both pieces are aligned the setting is in focus. Optimum sharpness is achieved when the contours and lines flow naturally. Incorrectly aligned edges indicate that the image is out of focus.
Micro prism
The micro prism ring blurs the image unless the lens setting is in focus. The drawback is that the micro prisms have considerable light loss, making low-light focusing almost impossible.
Zoom Ring
Zoom Lens
A zoom lens is a variable focal length lens where by turning the zoom ring the photographer can change the focal length (and thus the angle of view) within a pre-defined range (e.g. 10mm -120mm) whereas this cannot be changed with a "prime" or fixed focal length lens.
Magnification power of zoom lenses is often described by the ratio of their longest focal length to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 10 mm to 120 mm may be described as a 12:1 or "12X" zoom. A 12X zoom lens at maximum focal length (i.e. in this case when the lens is at 120 mm) can magnify the image 12 times of its image produced at its minimum focal length (i.e. when it is at 10 mm).
Exposure Control
Exposure is the total amount of light is allowed to expose the sensitive material (e.g. film or CCD or CMOS) to form the image.
Exposure is expressed as E = I X t.
[Where, “I” is the intensity of light passing through the lens and “t” is the time during which the light is allowed to fall on the sensitive material]
The aperture and the shutter are the two mechanisms that help exposing the photosensitive materials in a controlled manner.
Aperture/iris/diaphragm
In optics, an aperture is a hole or an opening through which light travels.
Aperture or Iris or diaphragm is a mechanism composed of overlapping strips of metal or plastic that, when spread apart, forms an opening of the same diameter as the lens; when meshed together, they form a small opening at the centre. Thus it controls the amount of light passing through the lens.
By turning the aperture ring light can be adjusted as per the f/number scale. In this f/number scale some typical f/numbers are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.
f-number or Relative aperture
f/number or the relative aperture is the ratio between the focal length and the actual opening of the lens.
e.g. for a 50 mm lens when the actual opening of the lens is 25 mm its relative aperture is f/2.
The smaller the f-number or stop, greater is the lens opening and greater the f-number, smaller is the lens opening.
The relation is the next adjacent higher f/no. cuts the light by half of the previous and the next adjacent smaller f/no. transmits double the quantity of light than the previous. That is at f/2 the amount of light passing is half of f/1.4 or double of f/2.8
The Shutter
Shutter as a mechanical device that controls the duration for which the light is allowed to expose the sensitive material (e.g. film or CCD or CMOS) to form the image.
Shutter has multiple functions. First, it protects the unexposed sensitive material from unwanted light. When operates, the shutter opens for a brief period of time and allows the light to expose the sensitive material and finally, it closes to protect the exposed material from further exposure.
Different kinds of shutters are used in cameras. They are mainly categorized according to their position in the camera.
In front of the lens shutter
Most primitive one is in front of the lens shutter. In early days mainly for plate cameras the lens cap itself was used as shutter to control exposure.
In between the lens shutter
Leaf shutter or Compur shutter are some of the example of the in betweens the lens shutter used in most non-interchangeable lens cameras or fixed lens cameras.
In these, shutter contained within the lens structure, often close to the diaphragm consisting of a number of metal leaves which are maintained under spring tension and which are opened and then closed when the shutter is released.
The exposure time is determined by the interval between opening and closing. In this shutter design, the whole film frame is exposed at one time. Disadvantages of such shutters are their inability to reliably produce very fast shutter speeds (faster than 1/500th second or so) and the additional cost and weight of having to include a shutter mechanism for every lens.
Focal-plane shutter
The focal-plane shutter is primarily associated with the single lens reflex type of cameras.
A focal-plane shutter is positioned immediately in front of the focal plane of the camera, that is, right in front of the photographic film or image sensor. It consists of cloth curtains that are pulled across the film plane with a carefully determined gap between the two curtains (typically running horizontally) or consisting of a series of metal plates (typically moving vertically).
Covering the film and blocking the light passing through the lens helps photographer to view through the lens at all times except during the time of exposure. Covering the film also facilitates removing the lens without affecting the film loaded in the camera.
Shutter Speed
Shutter speeds can be controlled by adjusting the shutter speed dial. Standards settings for shutter speeds are: 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, and 1000.
They indicate one part of the number i.e. 1/1 =1 Sec., ½= ½ sec, ¼ = ¼ sec., like 1/8 Sec, 1/15 sec, 1/30 sec, 1/60 Sec. 1/125 sec., 1/250 sec, 1/500 Sec. and 1/1000 sec.
Other controls in shutter speed dial are B and T. B stands for Brief time and T stands for Time Exposure.
B- Keeps the shutter open as long as the shutter release is held.
T- Keeps the shutter open until the shutter release is pressed again.
Focal–plane shutters
Using shutter and Aperture Together
Succeeding f-stop or increase in shutter speed cuts the amount of light in half; therefore a combination of shutter and aperture can be worked out together to substantiate an exposure. Equivalent exposures can be made with a larger aperture and a faster shutter speed or a corresponding smaller aperture and with the shutter speed slowed down.
Conclusion
In this lesson we have discussed the Essential Parts of a Camera like the Lens, Light Tight Chamber and View Finder and their controls. In that we have included Lens Controls that is controls with Focusing Ring, Aperture Ring, Zoom Ring and Control with the help of Shutter Speed.
Apart from controlling exposure the aperture can influence Depth of Field and shutter can control motion of moving objects. Those we will discuss in details in our next lesson.