Very few pros shoot headshots below f/5.6 and often more closed down than that.
I'm not sure that is what we see in general from the pros. More often for face on head shots we see f/3.5 - f/5.6 (and often wider) in my experience. Make for a very nice balance of DoF and isolation.
I am unclear who "we" are. If you are shooting a headshot with an 85mm or 50mm on a Z8/Z9 from 6 feet / 2m away you had better be close down unless you want more than 1.5" or 3.6" DOF. AND this is the point -- the distance to the subject AND the focal length AND then the aperture matter. Most headshots "have to have the front of the nose and the ears and bulk of the hair in reasonable focus, not just the eyes.
I accept style changes and as an old retired gezza what do I know. I learned in the 20th Century.
Just about every human image will have to have some post production -- most models do not have great skin and the rest of us have "imperfections" (sorry character) - I tend to shoot tethered to Capture One, which has the best tools for skin. I am not yet convinced by the skin softening tool s we now have in Z8 (and other cameras) - but then I shoot Raw and do not use NXS.
We also see many looking for emphasis on attractive boheka. Lens choice helps there. My fav is the 70-200 at near f/3.5.
As to focal length -- well this depends -- 1st on working space; the required content of the image (wide scene portrait -> tight cropped headshot or closer) and the age/roundness/roughness of the victim (sorry subject). I know a large number of pros who often "just" use a 70-200 on a 35mm/FF body - tending to the 85-135mm range for headshots of older folk like me for commercial clients AND others who use a nifty. Full-length portraits can be anything from 20mm to 200mm - most often 35mm-50mm when there is a scene/context and large dresses to include. In every case the brief will be agreed but always the product/model has to be in focus, the extent of out of focus of the rest depends on what the intent is. Hence the need for closed down apertures.
Lighting is always used in combination with the camera/lens comp to achieve separation.
I like the work of k of Dylan Patrick and there we see the 70-200 at f2.8.
There are many choices and options - we each get to pick what works for our own vision.
Dylan is known to shoot close to wide open.
Attend a few master classes with the likes of Peter H (Mr f/5.6), Rory Lewis, Pros at Wex/Calumet training etc... and/or spend a day with Peter Edwards and other celeb/event shooters and you will find out what settings are really used by them for commercial shoots and they start at f/5.6 and close down.
Distance to subject - is vitally important to understand -- Dylan wants a tiny sliver in focus. Most every other pro wants the whole of the head in focus and key jewelry and clothing in focus too.
These guys always work with strobes/speedlights and reflectors; almost never uncontrolled natural light.
All lenses have a sweet spot or range - one works to find it - most lenses a good at f/5.6-f/8. They are most certainly not "tuned" to shoot wide open. The 50/1.2 and 85/1.2 are sharper at 1.4 but not by much and then are quite good out until diffraction effects start to impact.
If you can back up and use a 200mm then sure one can shoot wider, but then you have to balance the light with the shutter speed and so often we shoot with an ND filter to keep the ISO at base and the shutter speed limited to 1/200th when using multiple speedlights rather than larger and more complex strobes. Most speedlights work best at 1/200th or lower shutter speeds. We almost always use reflectors and/or a strobe to provide a catch light and fill.
Some will avoid smaller apertures so that things like skin blemishes/imperfections are less sharp. And there are always exceptions
I have been playing with white and dark mist filters when there is multiple light sources in the image to provide a glow in camera, but more often than not we add this in post, while we (a retoucher not me) are fixing "skin" issues.
I also shoot X2D to access much higher/quicker flash sync speeds and these help control the ambient. My favorite lens for headshots is still the XCD 3.5/120mm (105mm FF eq) or the XCD 1.9/80mm (63mm eq) and we shoot at a range of apertures and lighting/shutter speeds to achieve a range of images from each set up. I can shoot the X2D down to f/16 and possibly f/20 on some XCD lenses before diffraction effects become really noticeable. The same is not the case for FX sized sensors.
