Basic Photography Theory.doc

7/28/2019 Basic Photography Theory.doc

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Basic Photography Theory

Aperture

Aperture is a device that controls the quantity of light that passes through

the lens. It is an iris type mechanism, which shrinks or grows in order to let inless or more light.

The numbers you usually see on a lens are:

F: 3.5 4.5 5.6 8 11 16 22 32

Each number lets in two times less light than the previous one.

Small numbers represent a large aperture, big numbers - small aperture.Most digital cameras do not have this numbers written on their lenses, butthey use aperture as part of their construction. It is also the way for you toselect aperture priority shooting mode from your camera to control the depthof field.

Shutter Speed

The shutter is a mechanism that controls the exposure time of an image. Thistime can be manually set by using the shutter priority shooting mode fromyour digital camera. The numbers you'll use will look probably like this:

15, 13, 10, 8, 6, 5, 4, 3.2, 2.5, 2, 1.6, 1.3, 1, 0.8, 0.6, 0.5, 0.4, 0.3,1/4, 1/5, 1/6, 1/8, 1/10, 1/13, 1/15, 1/20, 1/25, 1/30, 1/40, 1/50, 1/60,1/80, 1/100, 1/125, 1/160, 1/200, 1/250, 1/320, 1/400, 1/500, 1/640,

1/800, 1/1000, 1/1250, 1/1600, 1/2000 sec.

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These numbers represent how long the light will be allowed to hit the digitalsensor in order to capture the image.

ISO Speed

ISO speed shows how sensitive the image sensor is to the amount of lightpresent. The higher the ISO, the more sensitive is the image sensor.

The ISO is represented by numbers:

ISO 50 | 100 | 200 | 400 | 800 | 1600 | 3200

Each number represents two times the sensitivity than the previous one.Higher ISO settings are very useful in low light situations, but thedisadvantage of noise appears. The higher the ISO, the higher the noiselevels you get.

Shutter Speed 15 | Aperture 2 | ISO

Speed 50

Shutter Speed 15 | Aperture Value 2 |

ISO Speed 100

Shutter Speed 15 | Aperture Value 2 | ISO Speed 200

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ISO 50 Noise: ISO 100 Noise: ISO 200 Noise:

Image Stabilization

Image Stabilization is also known as vibration reduction and anti-shake; it is a technology found on digital cameras with long telephoto zooms(10X and 12X). It helps prevent images from becoming blurred.

This technology helps people in taking photos that require slow shutterspeeds. The system works in two different modes. There are systems thatstabilize the shot by moving the image sensor or by moving optical elementsinside the lens.

This anti-shake system can make the use of a tripod redundant, but there aresituations when at very slow shutter speeds (>1 sec.) the image stabilizationcannot cope with the movement of a hand held camera.

Image Format

Digital cameras store the images they produce in two different formats: JPEGand RAW. JPEG is the most common used image format, while RAW is usuallyused by professionals.

The differences between the two go beyond the image size. A JPEG image is acompressed image, for example, an 8 MB RAW image can be compressed toa 3 MB full quality JPEG.

The RAW format produces much more that a BIG image. It also has been

described as a "digital negative". Professional photographers use RAWbecause they can make later modification to the image that wouldn't bepossible using JPEG.

The disadvantage is the fact that you need specialized expensive software toread and modify RAW format images. You also need time and patience. Let'ssay that you make 100 photos in RAW format and 100 photos in JPEG.

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The JPEG images are ready to use, you may discard 20 of them because ofbad exposure, but you have the rest of the images ready to be printed or tobe published on the Internet.

With RAW images, you'll need at least 1-2 hours of opening the 100 imageswith photo editing software and tweak their properties to the point when

you'll get the image you want.

Focal Length

The focal length of a digital camera lens is the distance between the center ofthe lens and the image sensor when an in-focus image is formed. The focallength of a digital camera lens is displayed on the barrel of the lens alongwith the measurement of the largest aperture and the maker.

The focal length of a lens establishes the field of view of the camera. Theshorter the focal length is, the larger the field of view.

Camera lenses are categorized into normal, telephoto, and wide angle,according to focal length. Thus a 200 mm equivalent telephoto lens gives a 4x magnification over the 50 mm equivalent lens.

Depth of Field

Depth of field is the amount of distance between the nearest and farthestobjects that appear in focus in a photograph. In simpler term, we definedepth of field as the zone of sharpest focus in front of, behind, and aroundthe subject on which, when lens is focused on a specific subject.There are three key factors that have a direct relationship with depth of field:

Aperture Focal length of the lens

Image size

The general rule for selecting the right aperture for a desired depth of field is:given the same object distance and the image size, the bigger lens opening(aperture) used (like f/2.8, f/2, f/1.4 etc.) will have a narrower band of depthof field.

Depth of field increases with distance. The farther you place the camera fromyour subject, the more depth of field you can obtain. Landscapes have greatdepth of field, while macro photographs tend to have very little depth of fieldbecause the subject is so close to the lens.

White Balance

The white balance setting for a digital camera is very useful in dealing withvarious light conditions. The best way to understand this setting is to place awhite sheet of paper in front of your camera and take a photograph.

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If the image has a white sheet of paper in it, you're ok; but if the paper has ayellowish hue, you're in trouble.

To better understand this process, take a look at your lamp. It usually uses anincandescent bulb. If you look closely, you'll notice that the color of thisparticular source of light has a yellow hue. The digital camera amplifies this

hue and you get a yellowish photograph.

So, before taking any photo, look around at your sources of light. Even if youare outdoors, there are white balance settings that will make your photo looka lot better.

Daylight white balance

Cloudy white balance

Tungsten white balance

Fluorescent white balance

Flash white balance

Exposure Compensation

Exposure Compensation is a feature on a digital camera that allows you toadjust the shutter speed measured by its light meter. Usually, the range ofadjustment goes from +2 to -2 EV in 1/3 steps.

Lets say that you point the camera at you subject and the meter says youneed 1/250 sec. shutter speed at aperture 5.

If for whatever reason you select +1 exposure compensation, the shutterspeed used by the camera will be 1/125 sec.

If you use -1 exposure compensation, the shutter speed will be 1/500 sec.

Every increment in exposure compensation (+2 | +1 | -1 | -2) increases ordecreases the amount of light going through the camera by a factor of 2.

Red-eye Removal

In-Camera Red-Eye Removal finds and corrects red eyes caused by areflection of the flash off the cornea of the human eye. When the ambientlighting level is low, the pupils are large and red-eye occurs more frequently.

Having red-eye removal in the camera allows convenient correction ofpictures on the spot. Most of the time the system works, but there are timeswhen an entire group of people look like vampires on the prowl! There are noguarantees that using in camera red-eye removal function will help you takenormal looking pictures, but there will be a lot more of abnormal pictures ifyou do not use it.

Tripod

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When you should use tripods:

1. When your shutter speed is slower than 1/focal length of the lens. Thuswith a 50 mm equivalent lens, you should not attempt to handholdshutter speeds slower than 1/60 sec. and with a 500 mm equivalenttelephoto lens, you will have to keep the shutter speed at 1/500 sec. or

faster.2. In any low light conditions3. You need to use a tripod all the time if you want clear pictures in any

condition.

Batteries

When buying a digital camera always look at the type of batteries it is using.Some have large LCD screens, these consume a lot. Using the flash also cutsin half the time you are using the camera. If possible, buy a camera that hasspecially designed rechargeable batteries. These come with their own

charger and last a lot more than if you were to use normal AAA rechargeablebatteries.

NiCad Batteries

NiCad (nickel cadmium) batteries offer a relatively long life, high dischargerate and economical pricing, but they have distinct disadvantages as well.NiCad batteries must be completely discharged before they are charged ortheir performance per charge is diminished. You can expect around 700 ormore recharge cycles depending on usage; you should periodically cyclethese batteries through a complete discharge. Be aware that toward the endof their supply, they go from good power to zero power rather abruptly.

Lithium-Ion Batteries

Li-ion (lithium ion) batteries have long shelf life but in AA, AAA forms they arenot rechargeable. These non-rechargeable lithium batteries do last from oneand a half to 2 times longer than NiMH batteries; Lithium-ion (or lithium) isnot environmentally friendly and requires special disposal.

NiMH Batteries

NiMH (nickel metal hydride) batteries are the battery of choice for high drainapplications (digital cameras). They have a long life and can last from 500-

1000 charge cycles. Per charge cycle, NiMH will run one and and one half totwo times longer than alkaline. They are more robust and can be rechargedat any point in the discharge cycle. Nickel metal hydride is environmentallyfriendly, requires no special disposal procedures and contains no toxicmetals. Moreover, they are much less toxic during the recycling process.NiMH batteries are fairly expensive. They also lose their charge faster thanother types, if stored for more than a week, should be recharged before use.

Photographic filters

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Photographic filters have been in use for a long time. They were required forspecial effects or to enhance the contrast of some colors. They were alsoused for white balance.For example, a film set for daylight color temperature, would have producedyellowish photos when taken inside, with incandescent light bulbs lighting the

scene. To compensate, a blue filter had to be used, to get the right colors.

The major advantage of digital cameras is the fact that you can adjust thewhite balance of a scene electronically, without the use of a color filter. As faras the image effects that could be obtained with some filters (like blurring theimage, changing color hue for specific areas of a photograph, etc.) there arebetter ways of getting them onto a photo.

Very cheap image software can produce more effects on a photograph thanall the filters in the world combined. With a little bit of imagination, usingsoftware to get the effects you want is the best way to go.

The only filter a digital camera actually needs is a polarizer.

Polarizers come in two varieties: Linear polarizers

Circular polarizers

Each has the same effect but circular polarizers are more expensive. Digitalcameras can use both (linear and circular) polarizers.

Polarizers produce deeper colored blue skies, minimize light reflections fromglass and water and reduces glare from non-metallic surfaces. They also

provide good color saturation. Can be used in extremely bright lightsituations to reduce the amount of light entering the camera; this enablesmore selective depth of field control.

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Basic Photography Theory.doc