I have checked the video you've linked. My suggestion would be that this whooshing noise is not generated by the piezoelectric part but rather from the connected focusing mechanism (especially the helical focusing barrel which turns, and the focusing lens cell which slides back and forth. These parts sit inside the stationary lens barrel, and so a bit of friction is unavoidable. Just my guess.)
Syntax-wise, I will have to think about it. As with all my other articles, I like being very precise with physical formulas and mathematical expressions. But here is my point: These values in photography are not pinpoint precise anyway. When optical engineers come up with lens designs, the precisely calculated values for the aperture are something like f/4.63 which is then simply rounded to the next possible f-value specified on the lens barrel, and calculated focal length is often 25-49mm and Canon simply names that lens 24-50mm on the barrel (other manufacturers do that in a similar way). So, this is just my personal opinion, but it appears to me that in the context of photography, these values are just halfway decent guide values, almost like approximate descriptions of the lens behaviour. For that reason, I do understand why lens manufacturers move away from the precise syntax, and treat these values more like an abstract product description. Of course, if used in a strictly scientific context, I would rather prefer to use f/4.5. But I might be pretty alone with this view.
PS: I have planned a new chapter explaining all this, including the interesting fact that you've mentioned, where the diameter of the exit pupil actually changes according to the focal length, even with a constant aperture lens. But it will probably be end of summer when this is going online.
> this whooshing noise is not generated by the piezoelectric part but rather from the connected focusing mechanism
Indeed. I never implied that the piezoelectric part makes an audible whooshing noise. I only meant to say that the entire Ring USM system makes that noise, and so it will affect audio recorded on the camera's on-board microphone. Either way, that noise explains the motivation for the development of STM AF and I guess Nano USM.
Agreed with everything else you said. Thanks again for your fantastic articles and replies!
I have checked the video you've linked. My suggestion would be that this whooshing noise is not generated by the piezoelectric part but rather from the connected focusing mechanism (especially the helical focusing barrel which turns, and the focusing lens cell which slides back and forth. These parts sit inside the stationary lens barrel, and so a bit of friction is unavoidable. Just my guess.)
Syntax-wise, I will have to think about it. As with all my other articles, I like being very precise with physical formulas and mathematical expressions. But here is my point: These values in photography are not pinpoint precise anyway. When optical engineers come up with lens designs, the precisely calculated values for the aperture are something like f/4.63 which is then simply rounded to the next possible f-value specified on the lens barrel, and calculated focal length is often 25-49mm and Canon simply names that lens 24-50mm on the barrel (other manufacturers do that in a similar way). So, this is just my personal opinion, but it appears to me that in the context of photography, these values are just halfway decent guide values, almost like approximate descriptions of the lens behaviour. For that reason, I do understand why lens manufacturers move away from the precise syntax, and treat these values more like an abstract product description. Of course, if used in a strictly scientific context, I would rather prefer to use f/4.5. But I might be pretty alone with this view.
PS: I have planned a new chapter explaining all this, including the interesting fact that you've mentioned, where the diameter of the exit pupil actually changes according to the focal length, even with a constant aperture lens. But it will probably be end of summer when this is going online.