ISO
ISO or otherwise know ASA, is a measure of film or digital sensors sensitivity to light, it is commonly know as film speed.
ISO 100 graded film consists of very tiny grains of silver halide underneath an emulsion surface which react well to daylight, where as ISO 1600 film consist of larger grains of silver, better used in darker/night photography.
It applies almost identically in digital terms, on how quick the sensors reacts to available light.
The drawback to high iso numbers is a larger grainy effect on film during enlargement, or on a digital photo, due to the increased size of the silver halide or sensor area to compensate for low light levels.
Depth of field
Depth of field is the distance of focus, infront and behind the focus point.
If you are focused on a person, a low depth of field will mean only thing very closely (e.g 1 metre) infront and very closely behind with be in focus. A high depth of field is the opposite, and e.g 50metres either side of the focus point with be in focus.
Depth of field is also effect by the distance you are focusing away from the camera, greater zoom causes a lower depth of field.
Depth of field is control by Aperture size
Aperture
The opening of the lens is know as the Aperture. It is size/radius is calculated by what are know as f-stops.
Common apeture sizes are F1.4, F2.8, F5.6, F11, F22, each being exactly twice the size of the last. Most modern cameras accomidate further numbers inbetween. F4.5, F8, F16.
The apeture has two main functions.
Controlling the amount of light entering the lens due to size, and to apply artisitc depth of field to a photo.
The smallest aperture is F22, although the number implys that is would be the largest it isnt.
Higher numbers/small aperture size (F22) = greater depth of field, (more in focus)
Larger numbers/wider apertures (F2) = very low depth of field on a focused point.
(can include a chart i have of radius and size in mm of f-stops.)
Exposure timing
Where aperture was the size of the hole in the lens exposure timing is the length of time the lens aperture is held open for so that light can hit the film/sensor
It is calculated in hundredths of a second.
Common calculations are 1/1000 (one, onethousands of a second) 1/500 1/250 1/60 1/30 1/15 1/8 1/4 (quatre of a second) 1/2(half a second) 1 2 3 4 etc etc
Bright landscapes need lower exposure times (e.g 1/1000) to expose correctly (if long times are used the photo appears over exposed and white)
Dark landscapes need longer for the sensor/film to react (e.g 2seconds) because of a lack of available light
An example of how to use exposure timing and f-stops together is this
If a correct exposure at F5.6 is 1/500 of a second, and you want to increase the depth of field, so as to get more in focus, you would change the f-stop to F11 (remember higher numbers = greater depth of field) this however decreases the size of the aperture (high numbers = small aperture) so a smaller aperture means less light entering through the lens. You have essentially cut half the light out of the camera, so twice as long is need to expose correctly
The new exposure timing would be
F11 for 1/250, as F22 would be 1/125
It is common to apply an f-stop for artistic preference first, then find a suitable exposure timing for the film to expose correctly. The camera normally has a built in light meter to help this calculation
AWB
Known as automatic white balance, this is a feature found only on digital cameras,
White light from the sun has a temperature or level of light at 5500K, indoor lighting has a temperature closer to 3200k.
Rather than manually adjusting the white balance, according to the area you are photographing, the camera automatically senses the difference and adjust accordingly. If the white balance isnt adjusted then a blue or orange hue on all white areas of the picture. Most digital cameras also allow you to adjust manually.
Lens Numbers
You may have seen numbers on a lens such as this
70mm-300mm f4.5
The first set of numbers refers to the focal length of lens.
Focal length is th distance between the sensor/film and the apeture of the lens.
On fixed focal length this isnt changable, and only focus can be obtained.
Most lenses however are known as zoom lenses. They are capable of lengthening there focal distance, in this case from 70mm to 300mm, and anything in between. Accordingly a longer focal length gives a more powerfull zoom, and ability to focus into the distance.
The f-stop number is the lowest obtainable apeture size of the lens.
Fast lenses are so called by there ability to reach lower f-stop numbers such as 2. or 1.4
Can add these simple and quick explainations, i made.
Easier if anyone wants to correct any mistakes i might have made or reiterate what i said, as my english is fairly poor
