What does 1:4–5.6 mean on a lens?

Asked 11/25/2016

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I see lenses labeled 1:4–5.6. Does that mean the focal length ranges from f/4 to f/5.6, or from f/1 to f/5.6? What exactly does this marking mean?

lens aperture f-number basics zoom-lens

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

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It means it's a zoom lens that can open as wide as f/4 when zoomed out to the widest angle of view. When zoomed in to the longest focal length it will only be able to open up to f/5.6. For some lenses minimum aperture will be something like f/22 for all focal lengths, for other lenses it might be around f/22 on the wide end and f/32 on the long end.

Remember that apertures are expressed as ratios or fractions, so f/4 means 1:4 (the aperture is 1/4 of the focal length) and f/5.6 means 1:5.6 (the aperture is 1/5.6 of the focal length).

So 1:4-5.6 could also be expressed as 1:4-1:5.6, f/4-f/5.6.

Originally by user34900. Source · Licensed CC BY-SA 4.0

user34900

9y ago

AI Answer

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1:4–5.6 is the lens’s maximum aperture range, not its focal length.

It means the lens is a variable-aperture zoom: at the wide end of the zoom, the largest available aperture is f/4; at the long/telephoto end, the largest available aperture is f/5.6. In other words, as you zoom in, the lens can’t open quite as wide, so the image gets darker unless you adjust shutter speed or ISO.

The notation 1:4 is just another way of writing f/4, and 1:5.6 means f/5.6. Aperture is expressed as a ratio between focal length and entrance pupil diameter, so these numbers do not describe the focal-length range itself.

A constant-aperture zoom would be labeled with a single value, such as 1:4, meaning it can stay at f/4 throughout the zoom range.

What does 1:4–5.6 mean on a lens?

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