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Infinity Focus

When it comes to focal length and focus, is there really every distance to focus for?

Firstly, lets clear one thing up. “Infinity focus” doesn’t mean as far as the eye can see. Infinity in terms of focus is the point in the distance where everything beyond that point is equally in focus. Let’s say you are stood under a line of power-lines that have 100 pylons stretching into the distance. Now you can adjust your focus so the first second or third pylon is in focus. There will be a pylon, maybe 10 or 20 ahead of you. If you focus on this pylon, all the pylons after it will be in focus.

Focal length

Focal length refers to the angle of view of a lens. For example; a “17mm focal length” is wide angle, a “400mm focal length” is telephoto.

Shooting at 135mm (telephoto lens) it is difficult to acheive depth of field that covers everything. In this case the problem is solved by having a distant subject (the ice) so the background is fairly sharp.
Ice on the glacier lagoon

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Telephoto

This lens has a focal length of 135mm

Wide angle

This lens has a focal length of 24mm Canon
EF 24mm f/1.4L II USM Lens
Canon EF 24mm f/1.4L II USM

Focal length determines the point of infinity focus.
Different focal lengths will have a different infinity points. For example a 24mm lens will have infinity at around 20 meters whereas a 200mm lens will have infinity at 500 meters.

Depth of Field (DOF)

Depth of Field refers to the range of sharpness in a photograph. There is only one point of focus (focal plane) but the range of sharpness is determined by the Aperture, Focal length and distance to first object.

This Icelandic horse was shot at 135mm. Although the background is not far beyond the horse, the closeness of the subject created a blur in the background (Bokeh).

Icelandic Winter horse

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Dettifoss waterfall Iceland

Infinity is somewhere in the middle of the waterfall. Hyperfocal focus and small aperture was used to ensure sharp foreground and background.

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