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The focal length / f ratio / crop factor is a confusing one.
But why don't the camera and lens manufacturers not specify the actual FOV instead of the fake millimeters ? That is correct for every camera from medium format to cellphone.
So no 50mm f/4, but 46 degrees f/4.
And the Nikon P1000 is 84 to 0.7 degrees FOV.
But for exchangable lenses cameras with different sensor sizes (such as Canon EF for FF and APS-C and Nikon legacy mount for both FF and DX) the millimeter measure is better as it are real millimeters and the FOV varies between FF or APS-C.
And these f/ratio is even confusing some astrophotographers. The myth is that a telescope 80mm f/5 is 'faster' than 100mm f/5.6 and shows fainter stars and nebulas than the 100mm f/5.6 'because 5 < 5.6'.
Well, the sky background is brighter and due to the larger FOV. more stars are crammed in the field, but not fainter stars.
Remember that a high magnification eyepiece shows fainter stars than a low mag eyepiece on the same telescope ? Same principle.
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