Why does my APS-C need more light than my one-inch sensor??

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GivenToFly Junior Member • Posts: 35
Why does my APS-C need more light than my one-inch sensor??
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I have a Fuji X-T20 with a 35mm/f1.4, and a Canon G7x II. I was playing around with both cameras and noticed something very odd.  For example, I'll set ISO on both cameras to 800.  I'll zoom in on the G7x II so it has roughly the same FF equivalent focal length as the 35mm lens (roughly 55mm at FF equivalent).  I use spot metering for both.  I set the G7x II aperture to 2.8, and the X-T20 to the equivalent at 5.0.  I have no filter on the 35mm lens.  So theoretically, the shutter speed should be the same on both.  Yet, the X-T20 is always about 2 stops slower.  So if it's 1/20th of a second, the G7x II would be 1/80th of a second.  No matter what changes I make -- apertures, metering method, what I'm shooting, etc -- as long as the settings are equivalent once adjusted for sensor size, the X-T20 is always 2 stops slower.

What could possibly be going on here? How is it that the APS-C is always 2 stops slower than the one inch sensor? The only thing I can think of is I'm confusing something about the aperture setting on the X-T20, which numerically is about 2 stops slower than the G7x II (5.0 vs 2.8 in the example above), but I believe should be letting in the same amount of light when adjusting for the difference in sensor size.  But I don't think I'm misunderstanding that.

So what's going on here???  I'm so confused! 

Canon G7 X II Fujifilm X-T20
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