Depth of Field (DOF)

Depth of field refers to the degree of sharpness in front of and behind of the main subject when the main subject is in focus. Depth of field is affected by aperture, subject distance and focal length.

1. Aperture

Using a large aperture will result in a shallow depth of field. This is especially useful if you want to isolate the subject as the subject will be in focus and the background will be blurred. On the other hand, using a small aperture will result in large shallow depth of field as the main subject as well as in front of and behind the subject will be in focus. Use that when you want to take for example landscape.

2. Subject Distance

By moving nearer to the subject, the depth of field will be shallow. Likewise by moving farther away from the subject, the depth of field will be deeper.

3. Focal length

Using the same aperture but different focal length, you will find that a wide angle has a deeper DOF compared to the telephoto len.

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Through the len (TTL)

Through-the-len works by firing the flash at the subject. The reflected light will then enter the camera through the len (hence the name) and hit the film. Some of the light that bounces off the film will be captured by an off-the-film (OTF) sensor which reads the exposure. When sensor decided that there is enough exposure, the flash bulb switches off. This happens in a split second. This technology is made to fit in film in the olden day but with digital camera photography gaining popularity, different camera manufacturers begins to modify TTL to suit the digital sensor.

You might also be interested in reading how the through-the-len was developed, Canon flash system and Nikon flash system.

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Guide number

Guide number is commonly used as a standard to measure how far a flash can illuminate an object at a specific ISO and aperture. A high guide number indicates a powerful flash while a low guide number refers to a weak flash. Guide number is given in a formula as shown below:

Guide Number = distance x f-stop (at a specific ISO)

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Red eyes reduction

Red eyes effect is actually caused by a bright light striking at the back of the retina. The reflected light which the camera captured actually come from the blood vessels and hence, gives red eyes effect shown on the picture. Normally this can occur when you are at a low ambient light. To compensate for the low light, our eyes dilate or open up to allow more light so that we can see clearer. At this condition, if a flash is fired at the eyes, our eyes will not have the time to react to contract or close up. This causes red eyes effect. Almost most of the cameras are equipped with a red eyes reduction that eliminates red eyes effect. What red eyes reduction does is it will flash two times. One is before the picture is taken to allow the eyes to contract so as to reduce red eyes. Two is after the picture is taken.

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Chromatic Aberration

Chromatic Aberration refers to camera lens not focusing all the colour at the same focal plane. This occurs due to the different lens have a different reflective index for different wavelength. Chromatic aberration can be detected by looking at contrasty edges for any colour fringing and occurred frequently in wide angle shots, notably around the edges of the image frame.

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Image Stabiliser

The use of image stabiliser has become increasingly found in almost all digital cameras as well as certain lens. As the name suggests, it help to combat any hand shake. The piece of hardware known as a gyroscope is actually responsible for stabilising image either by moving an optical element or moving the digital sensor to redirect light path. Different camera manufacturers have included names like Optical Image Stabiliser (O.I.S by Panasonic), Vibration Reduction (V.R by Nikon) and Image Stabiliser (I.S by Canon) to tell consumers that the cameras or lens are equipped with image stabiliser. Some cameras and lens in-built image stabiliser have three modes to choose. You can switch off IS (Mode 1), turn on IS (Mode 2 which compensates horizontal and vertical motion) and use the IS for panning (Mode 3 which compensates vertical motion).

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Pinhole Cushion

Pinhole Cushion is an len effect that caused an image to constrict or squeeze towards the centre. The is effect is usually noticeable when the lines are close to the edge of the image and affects the tele end of the len. Pinhole cushion can be corrected by using Adobe Photoshop by selecting “Filter” > ”Distort” > ”Spherize”. The opposite effect is barrel distortion.

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Barrel Distortion

Barrel Distortion is a len effect that caused an image to become fat or spherical. This effect is usually noticeable when the lines are near to the edge of the image and affects most wide angle len. Barrel distortion can be corrected by using Adobe Photoshop by selecting “Filter” > ”Distort” > ”Pinch”. The opposite effect is the pinhole cushion.

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Vignetting

Vignetting refers to a loss of imaging area at the corner or peripherals of the frame. There are three reasons to explain how vignetting can occur:

Optical Vignetting – This is due to using a large aperture such as f/1.4 but this can be corrected by reducing the size of the aperture. The image resulted is a gradual darkening towards the centre.

Mechanical Vignetting – This is caused by light being blocked by external objects such as stacked filters, large hood attached to the len. The image resulted is a small dark area near the corner of the frame. To correct this, simply remove any obstruction to the len.

Natural Lighting – This is due to a law known as cos fourth law of illumination falloff. This falloff is proportional to the fourth power of cosine of the angle at which the light strikes the sensor. This form of vignetting cannot be cured by stopping down the len. vignetting often interrupt or distract but does not necessary mean it is when can be used draw viewer to centre of the frame>

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Sensor

Our eyes can capture red, blue and green – the primary colours. These colours are combined and represented the range of colours that we normally see in everyday life. In order to capture these range of colour, a sensor consists of three primary colour elements are needed. The sensor can be constructed into an array in which tiny parts known as pixels will be used to capture each of the three primary colours. There are two different types of sensor currently available and they vary in sizes:

CCD
It stands for Charge Coupled Device. Cameras available in the market either come with CCD or CMOS sensor. CCD sensor contains thousands or millions of tiny cells which transform light into charges. Charges are then transported and read at a corner using an analog-to-digital converter which will give a digital value. Each of this value will be stored and an overall image will be formed containing the different value.

CMOS
It stands for Charged Metal Oxide Semiconductor. The CMOS sensor made use of several transistors at each pixel that amplify and move each charge using traditional wires. Charges can be read individually and image will be formed.

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Crop Factor

Most digital cameras have sensors size smaller than 35mm frame. Pictures captured by a small sensor size will have a cropping effect as compared to 35mm frame. Because for this cropping effect, lens made for small sensors have shorter focal length. To measure crop factor, take the length/width/diagonal of the 35mm format divided by length/width/diagonal of the cropped sensor. In SLR, it is important to know what the crop factor is because you will need to know the correct focal length to purchase. For example, to obtain a 50mm in 35mm equivalent format, you will need to purchase a len that is about 31mm for a crop sensor of 1.6x. For compact camera, there will be a phrase “35mm equivalent” to tell consumers how wide and how far the camera can take.

For those who heard of 35mm format but wondered why the size is 36mm by 24mm is because
35mm format refers to the width of the negative film. 36mm by 24mm is the area that image will be captured.

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Metering

Metering refers to how camera measures the amount of light reflected by the scene. There are a few metering types that every camera model will have.

Evaluative or Matrix meter
This meter works by splitting the scene into smaller parts and then measures individual part. The overall exposure will be obtained by the camera algorithm. This meter is complex in a sense that although it works well in most case, it is hard to predict which parts of the scene the camera choose to obtain a proper exposure.

Centre-weighted average meter
The camera will meter the entire scene and average it but will give more weight towards the centre. This type of meter is ideal for portrait where the subject of interest is place at the centre.

Spot(Partial) Metering
Some camera will have both meter available. Although both perform the same function but the difference lies in the percentage of scene used to meter. For partial metering, it measures about 9% of the scene at the centre whereas spot metering measures about 4% at the centre. This metering is ideal for backlit object and moon shot which requires a small amount meter area.

You maybe interested to look at:
how to caliber exposure

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Memory Cards

Nowadays, there are a lot of memory card available in the market. Just to name a few, there are compact flash (CF) card, secure digital (SD) card, memory stick, multimedia card (MMC), smart media card, xD picture card. Take note that within each type of memory card, there are also variants (e.g SD cards have microSD, miniSD, SDHC). So pay attention to the type of memory cards that your camera can accept so as to avoid wrong purchase. There are some camera models allow selected memory cards to be slotted into the camera. If you happen to have an old model that uses a CF card and you purchase a new model that allows you use CF card as well as SD card, you can still use the same CF card in your new model.

You might wonder how many pictures can a memory can store. Below is an estimation of how many pictures you can store using different size memory cards. My advise is to get more capacity memory cards if the cards is worth the value to buy. Do not get the maximum size that the market can offer as they are expensive and it is risky to bring one large memory card along with you. It can be frustrating if you will to take an important picture and realise that the memory card malfunction. Instead, get an extra memory card of similar size as a backup. Do not get a high speed card as there is a limit that a camera can record image (i.e if the camera can record at 8x, do not get a 12x memory card as 8x is the maximum speed that a camera can record image).

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Compression

Sometime high megapixel does not necessary mean good quality pictures. It also have to depend on what are the setting you choose. In your camera setting, you can select the number mega pixels to take and this refers to how big your picture size is. If you want a good quality image, there is another setting that you need to take note of. Depending on the camera models, certain model may group both image quality and megapixel into categories like “L1, L2, M1, M2,etc” or separate functions like megapixels and quality (fine and normal). If you are unsure which setting will give you a good quality picture, you can refer to the amount of pictures the memory card can store in the LCD screen. Usually a high megapixel with low compression will take up a lot of space while the same high megapixel with high compression will take up less space. Here are some pictures taken at the same megapixels but with different compression to illustrate the quality of the picture. Bear in mind if you will to do a large printout, quality is very important.

This picture shows no much different in compression from an uncompressed picture.

This picture shows a little degradation in compression. If you save the picture and zoom in and compare the above image quality, you will see some lines appearing.

As the picture gets more compressed, you can see there is an obvious degradation in image quality. Try save the picture and zoom in. You can see some pixels showing up.

If you want to edit pictures, it is advisable to save under the lowest compression rate as possible so as to prevent image loss. Alternatively you can save under RAW format if you want to do a lot of editing such as changing white balance, exposure, etc.

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Focal Length

Focal length is explained as the distance between the centre of the len to the sensor when the object is in focus. It is commonly measured in millimetre. In digital photography, focal length can range from 6mm to 800mm depending on the size of the sensor. Focal length is often associated with perspective, that is, your background will be magnified if you use longer focal length. To illustrate this perspective, refer to this link to help you to understand. You may also interested in how different focal length will help you to determine how far you can shoot. Go to the Canon website and scroll all the way till you find the focal length section.

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Autofocus (AF) Servo

AF servo is part of the autofocus system normally found in prosumer camera, which allowed continuous focusing on the moving subject. It is useful in sports photography, animal photography, or any other moving object that requires continuous focusing in order to obtain sharp object.
To use AF servo, you must set your camera to AF servo. By focusing on the moving object and half-pressing the shutter button, the camera will continuously focus on the moving object. Usually AF servo is used together with continuous mode to take moving objects. This allows photographers to choose the best moving object out of a series of shots.

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Autofocus (AF) Assist Beam

Most camera manufacturers have incorporated autofocus assist beam into the camera to help it to focus in a low lit light condition. It is usually found on top of the len barrel and usually emits either an infrared light or a visible light with range usually up to 4 metres. For an external flash which can be mounted on top of the camera hotshoe, the range is usually long (Up to 16m). The AF assists beam can sometimes be double up as a red eyes reduction system by firing a strong light to allow the pupils to contract to reduce red eyes.

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Autofocus (AF) System

All cameras come with autofocus system. There are basically two types of autofocus system. Single AF allows the camera to focus on the object once while the continuous AF allows continuously focusing on the object and it is especially useful on moving objects. To achieve autofocusing, there are some points on the camera. Depending on the camera models, these points can range from 3 to 51. Some models also allow you to manually choose one of the autofocusing points to achieve selective focusing. If the auto focusing fails to detect any object, you can switch to manual focus. Manual focus allows you to do selective focusing also by either manipulating the len focusing ring (in SLR) or some setting that are found in compact camera. There is an AF assist beam available in most cameras that allow autofocusing possible in low light conditions.

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Multiexposure

Multiexposure refers to the camera ability to take multiple shot in the same frame. This feature is only available on selected models such as Panasonic LX3. What it does, you take different shots and the camera will merge them into one frame. This feature can be useful if you want to create some special effects such as taking a couple shot against the cloudy a background or different facial expression all in one frame. Try to experiment more and sometimes you may get an unexpected result.

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Exchangeable Image File (EXIF)

EXIF is used to store camera settings such as aperture, shutter speed, ISO, focal length used and etc. In short, it stored the setting used to take the specific picture so you do not need to worry about the setting used to take the camera as you can access them. You can access them either in imaging software that the camera make provides or you can right click on the picture and go to “Properties”, then to “Details” (This mode of accessing EXIF is in Window platform).

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