I point this out all the time. Just because a lens is great for photography does not mean it will also be great for videography. I know exactly what you mean by noisy apertures.
Most of the Canon older USM lenses in the EF lineup have remarkably loud apertures. Most people never notice it because the mirror slap usually drowns it out. But the mirror is not moving when you are capturing video, just AF motors and aperture blades.
As pointed out by Trevor, there is little you can do about reducing aperture noise besides moving your audio pickups away from the lenses and cameras. Using directional microphones is what I would recommend, instead of omnidirectional microphones, like you have on the front of cameras.
Many of the Canon EF mount USM lenses have loud apertures because the aperture does not change smoothly. Instead, it “steps” from one position to the next in a manner similar to how an aperture ring has click stops for each setting. The EF 24-105mm f/4L IS USM is one of the best examples of this “bad behavior.”
A handful of the EF mount USM lenses do have smooth apertures. The EF 35mm f/2 USM is an excellent for capturing video. Not only are aperture changes continuous and smooth, the lens is fairly quiet about it.
I recommend using fully manual lenses. Or, test or rent any future lenses befor you buy them.
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