Lenses

What is the basic function of lens and its characteristic?

In digital photography the lens is the most important part of a camera that takes the light that enters the camera and focus it on single point to form a sharp image/s. Its basic function is to admits a large amount of light permitting proper exposure in a small fraction of a second.

Lens Characteristics
Lens speed - refer to the amount of light that a given lens can transmit in a given time. The aperture part of the lens that controls the amount of light that reaches the film or CCD in digital camera.

Focal length- the distance from the center of the lens to the sharp image produce on the film plane or CCD when focused on infinity.

In digital photography Lens are classified as:
1. Wide angle lens- lenses with a focal length of 35 mm and below.
2.Normal lens- lens not particularly wide angle and not telescopic. For SLR camera lens of 50mm
is considered to be normal lens.
3. Telephoto Lens- lenses with a focal length longer than the normal lens (above 50mm focal length).
4. Angle of Coverage- Sometimes referred to as Lens Field of View- depends upon its focal Length - the longer the focal length the smaller the angle view.

Depth of Field

Depth of Field
Let us try to fully understand Depth of Field, in digital photography it is one of the most important aspect to consider since we already understand the exposure.

What is Depth of Field?

The depth of field (DOF) is the portion of a scene that appears sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on either side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

Depth of field (DOF) is the distance wherein objects are in focus.

This is the pragmatic explanation.

To be technically correct, DOF is the zone of acceptable sharpness, the area in front of, and behind, a focused subject that appears in focus.

Circle of Confusion (COF)

Technically, only the subject in focus -- and all other objects at the same distance -- are in focus; everything else in front and behind are out of focus. How much out of focus depends on a term called the "Circle of Confusion (COF, or COC)."

What Affects DOF

What we really want to know as photographers is what affects DOF so we can control DOF in our pictures. For a long, long time, photographers have gone with the following three criteria in digital photography:

• lens aperture
• distance from subject
• focal length

While the first two are technically correct, the third one has raised somewhat of a storm of controversy among certain circles. Why exactly, we will make clear later. Let's look at each of the three criteria in more detail.

A short depth of field can be very useful when you want to isolate your object from the background, such as when taking portraits or macro photography. A large depth of field is great when you photograph landscapes and overall when you want every detail to be in focus.

Control the Depth of Field

There are three variables that affect DOF in digital photography, the size of the Aperture, the distance to the object and what lens you’re using. (There is a fourth thing that affects the DOF, but that’s the size of the sensor and unless you have two cameras with different sensor sizes this isn’t something to take into account.)

Exposure: ShutterSpeed

In Digital Photography the shutter speed is one of the most important elements to consider to have a impressive shot, but let us understand fully how the shutter speed works.

What is shutter speed ?
The aperture diaphragm of a lens (bigger or smaller values) and timing (open and close) of the camera's shutter curtain - both perform the tasks of regulating the amount of light entering the camera and expose onto the film. The shutter speed scales engraved on the shutter speed dial of conventional camera bodies with a shutter speed ring OR via some flickering digital numerals on the LCD screen like: 1/8000, 1/4000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 or -1, -2 etc. are essentially indicators of the duration (timing) at which the shutter curtain opens up and closes during an exposure process. A 1/125 setting means the shutter curtain open and close within one hundred and twenty five of a second while 1 means an one full-second the shutter opens up during exposure to absorb the available light source onto the film to form an exposure.

What does shutter speeds do ?

In principle, shutter speeds, like aperture value detailed on earlier section, contributing as the next half of the main components for any exposure process - the interval at which the shutter opens to allow a specific amount of light (also depends on the opening of the lens diaphragm) to pass through and expose the film inside..

Different selection of shutter speeds will yield different kind of visual effect on a final photograph. Generally, a fast shutter speed can freeze action while slow speed can blur your image. I am not indicating these are fixed rules. If you understand the nature of how various shutter speed(s) will affect an exposure, you may put them to creative use to enhance the effect - like other than freezing a fast action scene, a slow shutter speed can also put to good use in portraying movement. You can try on to "PAN" a moving subject by following its direction or simply generates a sense flow of movement. But MOST people relates SLOW means BLURRING AN IMAGE which leave little for them to select this alternative to try them out. Well, it is excusable because in most PR-type of photography (photo session on public relation matters like wedding, gathering, seminars, or personal domestic duties for some privileged group - includes your wife, mistress or girl friends..), who would appreciate a defocus or blurry images ? BUT - for the creative minded photographer, slower shutter speed sometimes may create a more powerful visual impact than images taken with action-freeze high shutter speed(s), say, a free flowing river, traffic, a flock of birds taking off or even speed-demons on a race track.. etc..

A basic mechanical SLR camera body like the Nikon F2S of the mid-seventies only offers manual exposure control. AE may require accessory such as DS-1 to transform it into an shutter priority AE camera.

A camera operating in manual mode or a mechanical camera requires you to set the shutter speed and aperture value on the lens manually. In an automatic camera, there is usually at least one type of automatic exposure mode is available. Because of complication of mechanism involves, most camera manufacturers offer only Aperture Priority AE or Programmed AE modes on their EARLY electronic camera models. A good example is Minolta and Canon with their MD and FD mount cameras and lenses while in some exceptional case, such automation was made possible using a mechanical device such as Nikon's F2 with their EE Aperture Control Unit. However, by early '80 with development and refinement made on both cameras and lenses (Most would require a new series of optics), majority of them started to offer "Shutter Priority AE" and "Intelligent Programmed AE" as well.

Type of Camera

Types of Camera

The camera or camera obscura is the image forming device and photographic film or a electronic image sensor is the sensing medium. The respective recording medium can be the film itself, or a digital electronic or magnetic memory.

Photographers control the cameras and lens to exposure the light recording material (such as film) to the required amount of light to form a "latent image" (on film) or "raw file" (in digital cameras) which after appropriate processing, is converted to a usable image. Modern digital cameras replace film with an electronic image sensor based on light sensitive electronics such as "Charge couple devices" (CCD) or " complementary metal-oxide semiconductor" (CMOS) technology. The resulting digital image is store electronically, but can reproduce on paper or film.

You also need to choose the best camera for you, depends on your purpose. Learn digital photography in the step by step process.