Basic Photography Terms


You are not alone if you too are stuck trying to figure out the icons on your new-fangled digital camera and understand the photography terms your more ‘experienced’ friends are throwing at you.

Here are a few that you must understand to be able to exploit your camera’s capabilities to the fullest:

ISO:

In film-era, an ISO rating (also labelled as ASA) indicated the light sensitivity of the film. The lower the ISO, the lower the sensitivity. Hence more light required to get a properly exposed shot. ISO Rating typically was 100 / 200 / 400 / 800. ISO 100 film was used for daylight photography. ISO 200 was recommended for general-purpose photography (daylight, dawn, dusk). ISO 400 was recommended for Low-light photography (Dawn, Dusk, Interiors). ISO 50 and ISO 800 were generally sold as special purpose films.

Films with lower ISO rating had small photo-sensitive particles. Each particle had a small surface area; hence required more light for chemical activation. Films with higher ISO ratings had large photo-sensitive particles. The larger surface area of these particles allowed them to receive more light; hence get activated easily even in low light. A side effect of large particle size was the ‘grainy’ appearance of the images.

Digital ISO is similar to film ISO in behavior. Lower ISO settings result in smooth images but require more available light or slower shutter speeds. Higher ISO settings allow you to take hand-held images even in low-light conditions but the images are considerably more ‘noisy’.

Most Point & Shoot cameras (Sensor size less than 1/2.5″) shoot noise-free images at ISO 100-200. Noise shows it’s head in ISO 400-800. Images shot at ISO 1600 & more are quite noisy and are better presented as ‘journalistic’ images.

Crop Frame & Full Frame DSLR cameras produce images with very less noise up-to ISO 800. Images continue to be usable in ISO up-to 3200. ISO 6400 and above are very noisy.

The above Digital ISO quality ratings are very generalized. YMMV. New innovations in digital photography is reducing the noise and increasing ISO rating even in budget-cameras.

Shutter Speed:

Film cameras cover the film with a curtain to prevent light from activating the chemicals on the film unintentionally. The curtain is moved away for a brief moment when the shutter button is pressed. This brief absence of the curtain allows light to directly fall on the film surface and activate the chemicals; in essence taking a photograph.

DSLR cameras too use a curtain mechanism which is mechanically moved to allow light to fall on the sensor and allow the electronic sensors to record light data. The duration for which the curtain is moved away to allow light is known as the shutter speed.

Typically shutter speeds on a Point & Shoot budget digital camera range from 4″ – 1/160. This means that the shutter may remain open from up-to 4 seconds to 1/160th of a second. DSLR shutter speeds are more versatile with 30″ – 1/2500 being common.

If the shutter remains open for 4″ (4 seconds) in a daylight scene, too much light will fall on the sensor and the resultant image will be whited out. Similarly, if the shutter remains open for 1/160th of a second in a low-light scene, hardly any light will fall on the sensor and the resultant image will be practically black. Absence of Shutter for longer durations is called Slow Shutter Speed and absence of curtain for shorter durations is called Fast Shutter Speed.

If you are taking pictures while holding the camera in your hand, your hand’s movement will cause blurring of image. To prevent this, you should either 1) use a fast shutter speed 2) use a monopod / tripod to stabilize the camera.

To achieve perfect shutter speed, it is important to analyze the situation and decide if you are going to shoot hand-held or will you use a monopod / tripod to stabilize the camera. You can also increase the ISO setting and thus allow images to be taken even at fast shutter speeds.

Point & Shoot and MILC (aka 4/3rd, EVIL, CSC) cameras too employ a shutter mechanism but generally keep it moved away to enable live image preview. Since the shutter is not covering the sensor, the sensor continuously receives light and shows the image that it will capture in real-time. When the shutter button is pressed,the shutter moves in briefly allowing for a black period; which allows the sensor to capture a clean image.

Some cameras do not bother with moving the shutter at all. They simply take a snapshot of the sensor data and save it. Such mechanisms are called electronic shutters.

Aperture:

Aperture is the hole at the back of the lens which allows light to fall on the sensor. Lower aperture values mean bigger diameter of the hole and vice versa. An 18 – 200 mm Telephoto lens will typically have aperture range of 3.5 – 5.6. It means that at 18 mm (wide-angle) range, the aperture value is 3.5 (bigger diameter, hence more light allowed to fall on sensor) and at 200 mm (telephoto) range,the aperture value is 5.6 (considerably smaller diameter, hence less light allowed to fall on sensor).

Naturally, if the less light falls on the sensor, you will need to increase ISO (sensitivity to light) or select Slower Shutter Speed (shutter open longer to collect more light).

When a lens is focused, objects at a certain distance will be in sharp definition and objects in front & back (relative to object in sharp focus) will be out of focus and will appear blurred. This is defined as, Objects in the Focal Plane are sharply in focus. Typically, objects that are slight to the front / back are also relatively sharply focused. This distance range (relative to focal plane) is called Depth of Field.

The lens focuses light from the focal plane to pin-point accuracy. The combined effect of sharp light beams is a focused object. Light beams from out of focus objects tend to spread out and form large circles. The diameter of the light beams is called the Circle of Confusion. Lens that are capable of very sharp focus have very small Circle of Confusion.

In case of large apertures, the unfocused light beams tend to form large circles of light. Smaller apertures form smaller circles of light. This has the effect of sharper images in smaller apertures. Hence, at f3.5, the unfocused light beams maybe too spread out and overlap each other. At f16, the unfocused light beams are concentrated to form small blurred dots. When seen from a distance, these small dots may actually form the outline of the objects that are not in focus.

The blurring of the background is called a ‘bokeh’ effect and it is more pronounced in larger apertures (smaller f values).

When shooting portraits, products etc., it is desirable to keep the viewers attention on the subject. Hence, a soft bokeh is desirable. f numbers 1.4 – 4 are perfect for this. When shooting landscapes, jewellery etc., end to end sharpness is desirable and this can be achieve by using a smaller aperture (larger f values).f numbers 5.6 – 16 are perfect for this.

Note that, beyond a certain value for every lens, light beams tend to suffer from diffraction and no longer form smaller circle of confusion. As a result, each lens has an optimum f number at which it is at it’s sharpest. For this reason, pin-hole cameras produce soft images and not razor sharp images.

As a thumb-rule, most lenses produce sharper images when the aperture is two stop (f numbers) lower than the maximum. For example, a lens with maximum aperture of 3.2 is more likely to produce sharper images at f5.6 / f8.0 rather than f3.5. Premium lenses generally produce very good quality images even at their maximum aperture value.

Drive Mode:

Even the most basic digital camera today, offers multiple drive modes. The drive mode in older film cameras meant a combination of automatic film-advance and shutter action. Naturally, only expensive film cameras offered this option. In digital camera world, a drive mode is simply how many images are taken when the shutter is pressed.

‘Single Shot’ mode typically takes one image. If the camera is in auto-focus mode, a half-shutter press (press the shutter gently until it encounters a little resistance) generally causes the camera to focus the lens and full-shutter press activates the shutter once.

High Speed Continuous mode results in the lens focusing once on the object and the shutter is activated repeatedly as long as the shutter button is kept pressed. This is ideal for taking high-speed images of objects that are moving in parallel to the camera. For ex: horses on a race-track, vehicles on roads etc.

Slow Speed Continuous Mode also results in repeated shutter activations as long as the shutter button is pressed, but causes the lens to focus repeatedly on the subject between each shutter activation. This slows down the rate of shutter activations but also results in sharply focused objects. Use this mode for taking images of objects that are moving perpendicular to the lens. For ex: children running towards the camera.

Additional Drive Modes such as Self-Timer, Remote Shutter etc. too are available on most cameras.

Exposure Mode:

On most Digital Cameras, in Auto / Program / Aperture Priority / Shutter Priority / ISO Priority modes, the camera makes automatic calculations regarding one or more parameters related to ISO / Shutter Speed / Aperture Value. It does this by analyzing the light available in the scene.

The analysis is done on the basis of Full Frame (light is measured across many points in the whole frame to determine maximum and minimum light values), Center Frame (light values are measured in the center-area of the frame), Spot Metering (light value is measured in the center spot of the image).

Full Frame Exposure Mode is useful for broad daylight scenes which have bright light and dark shadow areas. Center Frame Exposure Mode is useful when the main subject is lit fairly well but the rest of the scene is either too dark or too bright. Typical use for Center Frame Exposure would be objects on stage. Spot Metering is useful for extremely difficult lighting situations like jewellery with bright sports, attempting to shoot the moon etc.

Closing Talk:

If you have understood these basic terms / features, you will be able to take images with an understanding of what worked and why.

Have a great time shooting!


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