Does focal length change perspective, or only camera position?
Asked 6/4/2024
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I often hear that focal length does not affect perspective, only camera position does. But using the thin-lens equation
1/s + 1/i = 1/f
and magnification m = i/s, it seems like two same-height objects at different subject distances would have a relative image-size difference that depends on focal length. That appears to conflict with the usual claim that focal length does not affect perspective.
Am I mixing up lens magnification with perspective in the final photograph? How should this be understood for normal shooting, and does anything change at macro distances?
Originally by cosaty. Source · Licensed CC BY-SA 4.0
cosaty
2y ago
2 Answers
2
A lens can only show the same view that you see when standing in that spot. A longer focal length will enlarge what the camera sees, but with the distances along the path all with their same proportional change, determined (or let's say affected) by their distance from where you are standing.
So Focal Length cannot change perspective. Your choice of where to stand (both angle and distance) is the only factor of what you will see there.
Originally by WayneF. Source · Licensed CC BY-SA 4.0
WayneF
2y ago
0
Generated from our catalog & community — verify before relying on it.
Perspective is determined by camera position, not focal length. If you stay in the same spot, the ratio of apparent sizes of near and far objects is set by their distances from the camera.
The confusion comes from mixing up two different things:
- the focused image formed by the lens
- the projection recorded on the sensor/film from that viewpoint
For perspective, what matters is the geometry from the camera position to the subjects. A longer focal length simply magnifies a smaller part of that same view; it does not change the distance relationships seen from that spot.
That’s why “zooming with your feet” changes perspective: moving the camera changes subject distances and angles, while changing focal length alone does not.
At macro distances, focusing and lens extension can change magnification behavior, but the core rule is the same: perspective still comes from viewpoint. Macro can make these effects more noticeable because distances are very small, but focal length itself is not what creates perspective distortion.
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UniqueBot
AI2y ago
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