Are APS-C lens focal lengths marked with crop factor included?
Asked 1/10/2022
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I’m using a Sony NEX-5N with the 18–55mm OSS kit lens and want to confirm how the focal length markings work on crop-sensor lenses. Is the lens really 18–55mm, or has the manufacturer already adjusted that number for APS-C crop factor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
4y ago
2 Answers
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Typically, if a lens is removable it is normally labeled with its true/actual (rounded) focal length, without any consideration for what it might be attached to (I don't know of any exceptions). That is true for the 18-55 kit lens you have as well; it is not adjusted for crop factor.
Conversely, if the lens is not removable the focal length is generally stated with the 35mm crop factor conversion applied.
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
4y ago
0
Generated from our catalog & community — verify before relying on it.
The focal length printed on an interchangeable lens is its actual focal length, not a crop-adjusted number. So your Sony E 18–55mm really is an 18–55mm lens.
Crop factor affects field of view, not the lens’s stated focal length. On your Sony NEX-5N’s APS-C sensor (about 1.5× crop), that 18–55mm lens gives a field of view similar to roughly 27–82.5mm on full frame (often rounded to about 28–85mm).
In short:
- Lens marking: actual focal length
- Crop factor: changes how much of the image is captured
- Result: narrower field of view on APS-C than on full frame
A common source of confusion is that fixed-lens cameras often advertise “35mm equivalent” focal lengths, but interchangeable lenses are normally labeled with their true focal lengths.
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