Lenses

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camera obscura /pinhole camera

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Focal length is the distance between the lens and the

point where the light rays converge. It

controls magnification and angle of view in a

picture.

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Focal length controls magnification and angle of view.

http://library.thinkquest.org/11355/html/typeslenses.htm

Normal (standard-focal-length)• It approximates human vision.

• It is fast, small, light-weight, less expensive than other lenses.

• With 35mm film or a full-frame image sensor, a 50mm lens is considered normal.

• The size of the film or image sensor determines what is considered a normal lens. The diagonal measurement of the film or image sensor equals the normal focal length. (For info on full frame sensor vs. smaller sensors: http://digital-photography-school.com/crop-factor-explained)

Long• A long lens will magnify far away

subjects.• It is heavier, bulkier, more expensive.

Focusing is more critical.• It can create pincushion distortion.

Short (wide-angle)• A short focal length (less than 50mm)

increases the angle of view.• It creates deeper depth-of-field.• It can cause barrel distortion.

http://www.dpreview.com/learn/?/key=barrel+distortion

35mm24mm

50mm 100mm

http://www.paragon-press.com/lens/lenchart.htm

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Focal Length and D-O-F

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http://images.google.com/imgres?imgurl=http://media.the-digital-picture.com/Images/Other/Focal-Length-Background-Blur.jpg&imgrefurl=http://www.the-digital-picture.com/Reviews/Canon-EF-180mm-f-3.5-L-USM-Macro-Lens-Review.aspx&usg=__CCYC_gK26QTtLWjiV532L8yirj0=&h=320&w=598&sz=50&hl=en&start=4&um=1&tbnid=R6hRQaj1lIYrmM:&tbnh=72&tbnw=135&prev=/images%3Fq%3Dfocal%2Blength%26hl%3Den%26client%3Dsafari%26rls%3Den-us%26sa%3DX%26um%3D1

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• Your distance from the subject also affects depth-of-field. The farther away you are from your subject, the deeper the d-o-f.

• Your distance from the subject also affects perspective (size relationships between objects). The closer you get to your subject the larger the foreground object will appear compared to the background objects.

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Prime vs. Zoom

• Prime lenses contain one focal length.• A zoom lens has many focal lengths

combined into one lens (e.g., 20mm-80mm, 24mm-120mm, 80mm-200mm). Remember when looking at a lens’ zoom capabilities only consider the optical zoom, not the digital zoom which will just crop the image.

Other Lenses

•Macro (or close-up filters): for focusing extremely close to an object.

•Fisheye: widest of wide angle lenses (180 degree view)

Review of Metering Considerations

• Substitution readings (grey card, exposure compensation, palm of your hand, spot meter)

• Backlit scenes (use light meter reading for silhouette; meter up close or use another substitution reading to get detail in your subject)

• Low light, high contrast• Bracket• HDR

Histogram: displays the distribution of tones in an image

from black to white

• This histogram shows an almost perfect distribution of tones covering about a 4 stop dynamic range — from deep shadows on the left to just short of bright highlights on the right. This fits comfortably within the approximately 5 stop dynamic range capability of most digital imaging chips.

• http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

Clipped Histograms

• http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

Underexposed Overexposed