Three Pillars of Photography• Aper ture• Shutter Speed• ISO (film speed)
Aperture• What is Aperture?• A hole within a lens through which light enters a camera body.• The aperture of a camera lens operates like the pupil of a human eye.• The larger the pupil the more light enters the eye. The smaller the pupil the less light enters.
• Small Pupil = Large f-stop number• Large Pupil = Small f-stop number
Aperture as F-stop• F-stop number is the ratio of focal length to effective aperture diameter. To determine a cameras f-stop you need to divide the camera lens diameter by its focal length.• Focal Length: Distance from front of lens to camera sensor when subject is in focus.• Focal length is stated in mm on the camera lens. A prime lens has a fixed focal length while a zoom lens shows a range of focal lengths.
F-stop continued• A camera with a lens diameter of 50mm and a focal length of 10mm would be f5 because the ratio is 50/10.• To change the f-stop would require a change in lens diameter by adjusting the aperture. 30mm diameter and focal length of 10mm would be f3 because the ratio is 30/10.
F-stop continued• A large f-stop number means a small opening and lets in less light.• A small f-stop number means a larger opening and lets in more light.• An f-stop like f1.7 is referred to as "wide open" and is considered "fast" because it lets a lot of light into the camera and allows for a faster shutter speed.
• What is Depth of Field? Depth of Field• It refers to the amount of an image that is in focus and is directly impacted by the cameras aperture.• The smaller the aperture (represented by a large f-stop number like f14) the more of the image will be in focus.• A larger the aperture (f1.7) isolates an object from its surrounding by making them blurry.• This is referred to as a "shallow depth of field"