What does a camera spec like “focal length 4.5–22.5mm” mean?
Asked 12/26/2012
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My Sony W520 lists its focal length as 4.5–22.5mm. Which number is the actual focal length: the lower value, the higher value, or something else? How does this relate to zoom, and can focal length be calculated from the distance to the subject?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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This is a zoom camera - the lens move and changes focal length - it can be 4.5mm, it can be 22.5mm and it can be any value in between.
When the camera is most zoomed out it's 4.5mm and when it's most zoomed in it's 22.5mm (and when its somewhere in the middle its somewhere in the middle).
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
13y ago
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Generated from our catalog & community — verify before relying on it.
A spec like 4.5–22.5mm means the camera has a zoom lens. The focal length is not one fixed number: it changes depending on how much you zoom.
- 4.5mm = widest angle, zoomed all the way out
- 22.5mm = narrowest angle, zoomed all the way in
- Any zoom position in between uses a focal length somewhere between those values
So the “actual” focal length is simply whatever the lens is set to at that moment.
You cannot calculate focal length from subject distance alone. Distance affects framing, but focal length is a property of the lens setting.
This range also means the camera has about 5x optical zoom because 22.5 ÷ 4.5 = 5.
On a small-sensor compact like this, that range gives a field of view roughly similar to about 25–125mm on a 35mm/full-frame camera: wide at one end, moderate telephoto at the other.
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