Why does a 50mm lens on my Nikon DX not look more zoomed than 50mm on my Sony APS-C?
Asked 8/19/2018
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I’m comparing a Nikon D3200 with a 50mm f/1.8 FX lens and a Sony a6000 with its APS-C 55–210mm lens. I expected the Nikon setup to behave like 75mm because it’s an FX lens on a DX sensor, so I thought it should look more zoomed in than the Sony at around 50mm. But in practice the Sony image appears narrower. Both cameras use APS-C sized sensors. Why is that?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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There is a general misunderstanding regarding sensors, lenses, and apparent zoom. The DX 3/2 zoom effect is misleading as nothing of the kind is actually happening.
50 mm is 50 mm, regardless of whether it's FX, DX, or large format.
A DX lens simply is not designed and built to have a high quality image or avoid vignetting over a larger area than the DX sensor, so it's cheaper and smaller to make. An FX lens provides good image over an area larger than the DX sensor, but that makes no difference whatsover on a DX as it's not seen.
The whole 3/2 zoom effect doesn't actually exist, the optics don't change. The perception comes about from cropping. A smaller sensor see less image. If you print or view this smaller crop area at the same size as a larger sensor, the result appears zoomed.
Originally by user77199. Source · Licensed CC BY-SA 4.0
user77199
7y ago
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Generated from our catalog & community — verify before relying on it.
Because a 50mm lens is still a 50mm lens, regardless of whether it’s labeled FX or DX. The FX/DX label mainly tells you the size of the image circle the lens can cover, not that the focal length changes.
On APS-C/DX cameras, field of view is determined by the actual focal length and the sensor size. Since your Nikon D3200 and Sony a6000 both have similar APS-C sensors, a 50mm lens on either camera will give nearly the same field of view.
The “75mm equivalent” number does not mean your Nikon lens becomes a real 75mm lens. It only means that a 50mm lens on APS-C gives about the same field of view as a 75mm lens would on full frame.
Also, your Sony 55–210mm lens does not go to 50mm—it starts at 55mm—so at its widest setting it will already look slightly tighter than the Nikon at 50mm. That’s why the Sony frame appears narrower.
So the key points are:
- FX vs DX does not change focal length
- crop factor is for full-frame comparison only
- 55mm on APS-C is slightly narrower than 50mm on APS-C
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