Some Photography Stuff

Types of Lenses:

Prime Lens - A lens with no “zoom.” While this might limit composition choices, it also usually means the lens is “faster” (meaning can achieve larger apertures, usually 2.8 and larger (2.0, 1.8, 1.4, 1.0, etc). The wider the aperture, the more light gets in and therefore the faster the shutter can be which is why primes are considered faster.

Zoom Lens - Any lens that can span a range of focal lengths. For example: 18mm-55mm. There are zooms in every category (normal, telephoto, wide, and macro).

Telephoto Lens - A lens that makes objects in the photo appear larger than they were to the naked eye. This is akin to being “zoomed in.” These lenses are comparable to physically moving closer to the subject. Some distortion can occur in the form of “compressing” the distance between objects.

Normal Lens - A lens where objects in the photo appear to be the same size as when seen by the naked eye. This lenses do not change your perceived distance from the subject.

Wide Angle Lens - A lens that shows a wider field of view than the naked eye. This is comparable to being further from the subject. Some distortion can occur (with a fisheye being an extreme example). Foreground objects appear disproportionately larger than background objects.

Macro Lens - A specialty lens that allows focusing on objects MUCH closer than with other lenses. Favored for all closeups (insects, flowers, etc).

Other Terms:

DOF - DOF stands for Depth-of-Field or Depth-of-focus. This describes how much of the shot is in focus (a plain perpendicular to the lens).

Focal Length - The size of a lens. Controls how “zoomed in” or “zoomed out” the picture is. On a 35mm camera a 50mm lens is pretty ‘normal’ and an 85mm lens is a short ‘telephoto’ and a 20mm lens is ‘wide.’ On a lower-end SLR a 50mm is a little bit telephoto.

Crop Factor - The ratio of size of the field of view between various cameras and compared against a 35mm film camera as the baseline. A typical digital SLR has a crop factor of 1.6 (meaning the field of view of the digital chip is smaller than a 35mm film frame). This affects the field of view offered by lenses. For example, a 50mm lens on a typical Digital SLR (DSLR) would be the equivalent of an 80mm lens on a 35mm film camera. A 200mm lens on a typical DSLR would be the same as a 320mm lens on a typical 35mm film camera.

Aperture - The aperture is the size of the opening of the shutter when it fires. It is measured as a fraction (so that 4.0 really means 1/4.0 and 16 means 1/16 and 1.8 means 1/1.8). The smaller the number, the wider the aperture. The wider the aperture, the smaller the DOF and the more light that gets in so the faster the shutter needs to be set.

Shutter Speed - How fast the shutter fires. Conventional wisdom dictates that a camera can be handheld at a shutter speed equal to 1/x where x is the focal length of the lens. For example, if shooting with a 100mm lens, you can handhold the camera up to 1/100 sec. Anything slower (1/50 sec, etc) would need to be balanced on a tripod or monopod or other stabilizer.

ISO - How sensitive the chip is to light. The higher the ISO, the faster the shutter can be set at. ISOs over 200 can start to introduce digital noise (comparable to film grain) with more noise coming from higher ISOs.

Exposure:

There are 3 major factors that affect proper exposure: ISO, Shutter Speed, and Aperture. Adjusting any of these factors affects exposure unless compensated for by either of the other settings.

For example, take the “sunny 16 rule.” The sunny 16 rule is a generalized rule of thumb for achieving proper exposure in sunny conditions. It states that you set the shutter speed to 1/ISO (ie - if using ISO 200 then set the shutter to 1/200 sec), then set the aperture to 1/16 (f-16 or f/16). So a proper exposure would be ISO 200, 1/200 sec, F/16.

Now if you wanted to change the shutter speed because you are using a 300mm lens and don’t have a tripod you could set the shutter to 1/400 sec. This would unbalance the above equation, so you could then compensate by raising the ISO to 400. Now you have ISO 400, 1/400 sec, F/16. Both this setting and the one above give the same exposure.

Depth of Field:

Depth of field is affected by two details: aperture and distance between the camera and the subject. Of these, aperture is the factor that gets manipulated most often when trying to change depth of field, however distance between the lens and the subject has a greater effect. The wider the aperture, the smaller the depth of field. When a lens is “wide open” (using the widest possible aperture, the smallest number) is has the smallest DOF; similarly, the closer the camera/lens is to the subject the smaller the DOF. Knowing how to limit the DOF is useful for blurring backgrounds and drawing focus where you want it. On the other hand, the smallest possible aperture (anywhere from F/16 on most lenses to F/22 or even F/45 on some lenses) gives the longest DOF. This is most useful in landscape photography where the ideal is to have ALL of the scene in focus.

Distance between camera and subject becomes an issue when shooting Macro photography specifically. When the lens is w/in mere inches from the subject then even a “normal” aperture like F/5.6 can yield a small DOF (a scant couple millimeters). To get all of a macro subject in focus it is usually necessary to shoot a F/8 or F/11 or smaller. This results in slow shutter speeds (see above) unless additional light is brought in (ie - from a flash). Slow shutter speeds increases the chance for motion blur (especially on a breezy day or when the subject is animate, ie a butterfly).