Why do a 15mm EF-S lens and a 24mm full-frame lens have the same angle of view?
Asked 4/9/2013
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I thought focal length always determined angle of view, but Canon lists these two lenses with the same horizontal field of view of 74°:
- Canon EF-S 15-85mm f/3.5-5.6 IS USM at 15mm
- Canon EF 24mm f/1.4L II USM at 24mm
Why can lenses from the same manufacturer have the same angle of view at different focal lengths?
Originally by user19253. Source · Licensed CC BY-SA 4.0
user19253
13y ago
2 Answers
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They're measuring the first on a crop-sensor camera and the second on a full-frame; specifically for a Canon APS-C sensor, 15mm x 1.6 = 24mm.
Canon does this in general when referring to EF-S vs. EF lenses; see for example How can a 24-70mm and a 10-22mm both be "wide angle" lenses?, which has the same effective answer.
The relationship between focal length and angle of view is fixed, for a given sensor size. More on this at What is “angle of view” in photography?, if it's not already clear.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
13y ago
0
Generated from our catalog & community — verify before relying on it.
Because angle of view depends on both focal length and sensor size, not focal length alone.
The EF-S 15-85mm is designed for Canon APS-C cameras, which use a smaller sensor (about 1.6× crop compared with full frame). Canon states its angle of view using that smaller sensor size. The EF 24mm lens is designed for full-frame cameras, and its angle of view is stated for a 36×24mm sensor.
So a 15mm lens on Canon APS-C gives about the same framing as a 24mm lens on full frame, since 15 × 1.6 ≈ 24.
In short: the focal-length-to-angle-of-view relationship is fixed only for a given sensor size. Change the sensor size, and the angle of view changes even if the focal length does not.
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