Quote:
Originally Posted by Atmos
The "crop factor" is a bit of a misnomer as it doesn't really do anything other than describe field of view differences.
Take a telescope for instance. I have a 130mm F/5.2 refractor which I have used with multiple cameras; ASI1600/QHY163M, Nikon D7200 and Nikon D810/ASI094. The first is a M4/3, the second APS-C and finally the last is FF.
Using the crop factor logic I have a 2x (1350mm), 1.6x (1080mm) and 1x (675mm). In all of this the aperture, focal length and focal ratio have not changed and it doesn't matter what camera you have, it has no affect on the focal ratio because neither the physical focal length or aperture have changed.
Now you are correct in that TECHNICALLY using the crop factor would make it a 130mm F/10.4 IF you were to use absolute comparisons between a M4/3 and a FF. This is only applicable if you're saying one lens is like another (your first comparison).
You're camera isn't misleading you though because you're not talking back technicalities about actually taking photos. Using an APS-C doesn't magically change a 50mm F/4 to a 80mm F/6, only that you would get the same amount of light output and FOV as a 50mm F/4.
In real life you are still shooting with a 50mm F/4 because your lens has a 12.5mm aperture and a 50mm focal length regardless of whether you're using a M4/3. an APS-C or FF.
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Thanks, but the crop factor - applied to focal length and to f number - describes the field of view and depth of field equivalences/characteristics.
At constant ISO, a 50mm F/4 lens in an APS non-Canon camera gives the same image on the sensor as a 75mm f/6 lens on a full frame camera. And a 50mm f/4 lens on a full frame camera gives the same image as a 33.3mm lens f/2.66 lens on a non Canon APS camera.
And putting each of your cameras in your telescope (which I'm very envious of) and taking pictures of the moon, will give images 1.6X and 2X bigger with the smaller sensor cameras than that with the full frame camera.
Plainly effective focal length has changed, while the lens's actual focal length hasn't.
f number is meant to be a dimensionless number that enables one to get equivalencies between lenses. Without taking effective focal length into account, the equivalencies disappear.
Regards,
Renato