Technics

Technics 

Shutter Speed

In photography, shutter speed or exposure time is the length of time when the film or digital sensor inside the camera is exposed to light, also when a camera's shutter is open when taking a photograph,The amount of light that reaches the film or image sensor is proportional to the exposure time. 1/500th of a second will let twice as little in as 1/250th.

What is shutter speed and what does it do?

Shutter speed is a measure of how long your camera’s sensor (the digital equivalent of film) is exposed to light.

Most DSLRs use a mechanical shutter to control this. When you press the shutter release button or use the camera’s self-timer function, the blades that block the sensor open and close, letting light in.

How long should the shutter be open?

It depends on the amount of light that’s available. Typically, lower light levels demand longer shutter speeds while brighter conditions require much shorter shutter speeds to make an exposure.

Significantly, the choice of shutter speed also has an impact on how movement is recorded in the picture.

The longer the shutter is open, the greater the likelihood there is of any movement being blurred.

As a rule, you’d use the fastest shutter speeds for fast-moving subjects, to stop the motion and make sharp pictures. But rules are meant to be broken!

You can select from a much wider range of shutter speeds than the one suggested by the camera.

What do you mean?

Say you’re shooting action, such as a horse galloping or a car on a race track. To get a sharp shot, you may need a shutter speed close to 1/1,000 sec or 1/2,000 sec.

Freezing the action this way might reveal detail you’d miss with the naked eye, but it can also rob a scene of its sense of speed.

Using a slower shutter speed would allow the shutter to stay open for longer, and some of the moving parts to become blurred – an effective technique for action photography when combined with ‘panning’.

By moving the camera so the subject stays more or less in the same position within the frame, it will remain sharp, while the moving background will be rendered as a blur.

How do I know which shutter speed will produce the best effect?

It depends on the speed at which the subject is moving. It’s often a fine line between the perfect blend of blur and sharpness, and something that looks like a mistake.

That galloping horse? 

You can probably get away with 1/50 sec for a panned shot, but a Formula One car would still need a nippy ‘slow’ shutter speed in the region of 1/500 sec for a similar degree of blur.

A monopod or an image-stabilised lens helps to support the camera at these lower speeds, ensuring a smooth pan in one direction.

In addition to its effect on exposure, the shutter speed changes the way movement appears in photographs. Very short shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for effect.Short exposure times are sometimes called "fast", and long exposure times "slow".

Adjustments to the aperture need to be compensated by changes of the shutter speed to keep the same (right) exposure.

In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1/10 s, 1/25 s, 1/50 s, 1/100 s, 1/200 s and 1/500 s; neither were apertures or film sensitivity (at least 3 different national standards existed). Soon this problem resulted in a solution consisting in the adoption of a standardized way of choosing aperture so that each major step exactly doubled or halved the amount of light entering the camera (f/2.8, f/4, f/5.6, f/8, f/11, f/16, etc.), a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the amount of time of the shutter speed by one step resulted in the identical exposure. The agreed standards for shutter speeds are

Aperture 

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane.If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp for things at the correct distance. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time). In the human eye, the pupil is the aperture.

An optical system typically has many openings, or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.

In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100 centimeter aperture. Note that the aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a relatively large stop to be the aperture stop for the system.

Sometimes stops and diaphragms are called apertures, even when they are not the aperture stop of the system.

The word aperture is also used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy for example, a photometric aperture around a star usually corresponds to a circular window around the image of a star within which the light intensity is assumed.

Depth of Field 

Depth of field refers to the range of distance that appears acceptably sharp. It varies depending on camera type, aperture and focusing distance, although print size and viewing distance can also influence our perception of depth of field. This tutorial is designed to give a better intuitive and technical understanding for photography, and provides a depth of field calculator to show how it varies with your camera settings.

The depth of field does not abruptly change from sharp to unsharp, but instead occurs as a gradual transition. In fact, everything immediately in front of or in back of the focusing distance begins to lose sharpness — even if this is not perceived by our eyes or by the resolution of the camera.

Since there is no critical point of transition, a more rigorous term called the "circle of confusion" is used to define how much a point needs to be blurred in order to be perceived as unsharp. When the circle of confusion becomes perceptible to our eyes, this region is said to be outside the depth of field and thus no longer "acceptably sharp." The circle of confusion above has been exaggerated for clarity; in reality this would be only a tiny fraction of the camera sensor's area.

When does the circle of confusion become perceptible to our eyes? An acceptably sharp circle of confusion is loosely defined as one which would go unnoticed when enlarged to a standard 8x10 inch print, and observed from a standard viewing distance of about 1 foot.

At this viewing distance and print size, camera manufacturers assume a circle of confusion is negligible if no larger than 0.01 inches (when enlarged). As a result, camera manufacturers use the 0.01 inch standard when providing lens depth of field markers (shown below for f/22 on a 50mm lens). In reality, a person with 20/20 vision or better can distinguish features 1/3 this size, and so the circle of confusion has to be even smaller than this to achieve acceptable sharpness throughout.

A different maximum circle of confusion also applies for each print size and viewing distance combination. In the earlier example of blurred dots, the circle of confusion is actually smaller than the resolution of your screen for the two dots on either side of the focal point, and so these are considered within the depth of field. Alternatively, the depth of field can be based on when the circle of confusion becomes larger than the size of your digital camera's pixels.

Note that depth of field only sets a maximum value for the circle of confusion, and does not describe what happens to regions once they become out of focus. These regions are also called "bokeh," from Japanese (pronounced bo-ké). Two images with identical depth of field may have significantly different bokeh, as this depends on the shape of the lens diaphragm. In reality, the circle of confusion is usually not actually a circle, but is only approximated as such when it is very small. When it becomes large, most lenses will render it as a polygonal shape with 5-8 sides.