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: Aperture

In Digital Photography the exposure is the most important aspect to consider by the photographer. Exposure mainly composed of three basic thing Aperture,Shutter speed, and ISO, but let us focus first in the Aperture.

Let us first understand the what is the effect of aperture in Digital Photography.

What Is... Aperture?

When you look at the technical specifications of a digital camera, one of the very first specification mentioned is its maximum aperture and/or its aperture range.

What is 'aperture,' what is a good aperture range, and how is aperture relevant when it comes to choosing a digital camera?

What Is Aperture?

Aperture is expressed as F-stop, e.g. F2.8 or f/2.8. The smaller the F-stop number (or f/value), the larger the lens opening (aperture).

[Note: Many camera user manuals today will refer to the aperture in terms of "aperture value" instead of f/value. I'm not sure when this trend started but don't get confused between "aperture" and "aperture value." Aperture value" is simply another way of saying f/value.]

In practice, unless you are dealing with a fixed-aperture lens (many simple point-and-shoot cameras have only one fixed aperture), the aperture of a lens is usually expressed as a range of fstops.

When you read the specifications of a camera, the aperture may be expressed in a number of different ways, the following three being the most common:

• Maximum Aperture:

Max. Aperture

F2.8

This simply states that the maximum aperture for the lens is F2.8.

• Aperture Range:

Aperture Range

F2.8-F8.0

This states the max. and min. aperture, the assumption being that there are standard increments between them.

• Maximum Wide-Angle and Telephoto Apertures:

Aperture

F2.8-3.5 or F2.8(W)-F3.5(T)

This gives the max. aperture for the wide-angle (F2.8) and telephoto (F3.5) focal lengths of a zoom lens.

It is usually not too difficult to figure out that a stated range deals with maximum apertures and not max and min apertures: the mimimum aperture should be quite small at F8, F11, F16 or F22.

A "fast" lens is one that has a large maximum aperture (F2.4, F2.0 for current digital cameras; F1.4, F1.2 for 35mm film cameras.

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.