Why does DPReview show the Canon G7 X II as about f/8 at 100mm?
Asked 5/6/2016
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My Canon G7 X II is advertised as having a 24-100mm equivalent lens with a maximum aperture of f/1.8-2.8. On DPReview charts, though, it appears closer to about f/8 at the 100mm end. Why is there such a big difference?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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The actual focal length range of the lens on your G7X II is not 24-100mm, it is 8.8-36mm. Coupled with the smaller sensor (13.2 x 8.8 mm) of the G7X II the 8.8-36mm lens gives the same field of view as a 24-100mm lens does on a full frame (36 x 24mm) camera. Similarly, the aperture of f/1.8-2.8 will behave, in terms of Depth of Field, like an aperture of f/5-7.78 when used with the smaller sensor (this equivalence breaks down at macro distances and distances past the hyperfocal point). In terms of exposure, however, it will still be an f/1.8-2.8 aperture.
For more about why many zoom lenses have variable apertures across their focal length range, please see Why do zoom lenses and compact cameras have varied maximum aperture across the zoom range? and Why does my aperture setting change as I zoom on my DSLR kit lens?
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
0
Generated from our catalog & community — verify before relying on it.
DPReview is likely showing an equivalent aperture, not the lens’s actual light-gathering f-number.
On the G7 X II, the lens is physically about 8.8-36mm, not 24-100mm. Canon quotes 24-100mm as the full-frame equivalent field of view because the camera uses a much smaller 1-inch type sensor.
The actual maximum aperture is still f/1.8-2.8, and for exposure it behaves exactly like f/1.8-2.8. So at the long end, the lens really is f/2.8 in terms of shutter speed and ISO.
What changes is depth of field equivalence. Because of the smaller sensor, f/2.8 on this camera gives depth of field similar to roughly f/7.8 on full frame at the same equivalent framing. That’s why a chart may show something near f/8 at the “100mm” end.
So:
- actual lens aperture: f/1.8-2.8
- full-frame equivalent focal length: 24-100mm
- full-frame equivalent depth-of-field aperture at the long end: about f/8
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