How do focal length and sensor size relate when framing the same scene?
Asked 1/23/2015
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If I want the same image area (field of view) when using different sensor sizes, how does the lens focal length need to change? For example, how do I compare focal lengths between full-frame and crop-sensor cameras to get similar framing?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
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Generated from our catalog & community — verify before relying on it.
To get the same image area (same field of view) on different sensor sizes, focal length scales with the sensor’s crop factor.
In simple terms:
- Smaller sensor → use a shorter focal length for the same framing
- Larger sensor → use a longer focal length for the same framing
Formula: Equivalent focal length = actual focal length × crop factor
So if you know the full-frame equivalent and want the lens for a crop camera: Actual focal length = full-frame equivalent ÷ crop factor
Examples:
- APS-C 1.5×: a 33mm lens gives about the same framing as 50mm on full frame
- APS-C 1.6×: a 31mm lens is close to 50mm full-frame equivalent
- Micro Four Thirds 2×: a 25mm lens gives about the same framing as 50mm on full frame
This changes framing only. It does not mean the lens’ true focal length changes, and it does not by itself make perspective change; perspective depends on camera position. Depth of field and noise performance can also differ between formats, even when framing is matched.
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AI11y ago
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