This article presents the inventive solutions Canon has found to shoot beams of light into the camera's viewfinder in order to light up individual autofocus points. Six different approaches are shown using six Canon DSLR models between 1994 and 2009.
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.
As far as I know, Canon controls a large part of the supply chain and has numerous factories to manufacture quality-critical parts (especially their lenses, zoom mechanisms, and barrels) themselves. But there are numerous components that are more efficient to obtain from third parties, such as microchips. I am not sure about the motors and actuators, though.
Thanks nayuki for the detailed comment and positive feedback.
Thanks for pointing out the missing EF-M, I am going to add that during the next polishing round. With regards to USM noise, the ultrasonic whine can be picked up by very good ears. I think the Nano USM is excited in the range of 60+ kHz, so at least that type of USM motor is absolutely inaudible.
Syntax-wise with F2.8, you got me. I know it's not 100% correct, but it was a deliberate choice that I made. Historically, there is either 1:2.8 or f/2.8 which will always be correct representments of the aperture (exit pupil) diameter. However, pursuing a cleaner look, I avoided the division or slash characters because the relation between the focal length and the f-number is known by every photographer. This is why Canon has also made the transition to the syntax "F2.8" in all their RF and RF-S-lenses - at least their product names and labels printed on the lens barrels. (The same is true with the focal length where Canon doesn't print "mm" on the barrel - to achieve a cleaner less mathematical look). So I believe what I did here was just go with the trend :-)
Thanks for your feedback. Until now I have never blogged about the creation of these illustrations, but it's a nice idea, there is tons of "behind-the-scenes" material. With regards to the viewfinder image, the actual path of light was drawn with the help of a Japanese optical engineer who was able to provide professional raytracing simulations.
Cool videos, thanks! The driver shown in the first video is indeed a piezoelectric actuator, but not the type Canon uses in their lenses. The driver shown in the second video is probably related to Canon's Nano USM.
turnsout Thank you very much. Trying to understand complex things has always fascinated me. Indeed it takes a lot of time (rd. 1.600 hours for the complete series of Canon lens chapters) but its people like you who drive me forward. I don't have a donation page yet, I never thought it would be used :-)