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Sharpness - Bokeh
Foto tutorial (English)
Foto tutorial (Espaņol)
Equipment recommendations US-ES
Flaat for Canon
Flaat for Nikon
Flaat for the BMC
Flaat for NEX-5N
Old Picture Style Tests
550D video lineskip
APS-C vs Full Frame
Badly assembled lenses and image quality
Lens mount compatibility chart
ISO on different cameras
High ISO on the 5D3
DIY: DR test chart
RGBWK Bayer sensors
Notes on DoF-FoV
Notes on crop-DoF-FoV
Custom Cropmarks for Magic Lantern on the Canon 550D
How many megapixels do I want?
How many megapixels can I see?
Quick Monitor Calibration Chart
Imagine the following scenario: you want to take a closeup (head and shoulders) of a person in the middle of the town square, with a building in the background.
If you take the picture with a wide angle lens (e.g. 28mm equivalent) you'll have to get the camera quite close to the subject, and the building in the background will look small in relation to him, giving the impression that it is relatively far away.
If you take the picture with a telephoto lens (e.g. 80mm equivalent) you'll have to stay farther away from the subject, and the building in the background will look relatively big, as if it was closer to the subject.
This picture was taken with an equivalent focal length of 28mm
And this picture was taken from farther away, with an equivalent focal length of 80mm
An important corollary of this is that for portraits it is usually best to use relatively long lenses (at least 80mm equivalent, preferably more, e.g. 150mm), because shorter focal lengths distort the face (making the central part wider, the nose bigger, and the ears smaller). You can see some very interesting tests here.