Depends a lot on the lens itself, really. 80% of lenses will perform their best at f/5.6-f/8
But for large aperture lenses, stopping down by 1-2 stops can already be enough. So an f/1.4 lens could already perform very well at f/2 - f/2.8, and an f/2.8 lens could already be very sharp at f/4, etc etc etc
The stopping down 2-3 stops is a general rule of thumb. There are some ( often pricier ) lenses built to be great performers wide open.
But most of the time, I am not really too bothered about that. More often than not aperture would be determined by what u want to shoot and how much dof u require. ( than working around from what the lens is better at )
Depends a lot on the lens itself, really. 80% of lenses will perform their best at f/5.6-f/8
But for large aperture lenses, stopping down by 1-2 stops can already be enough. So an f/1.4 lens could already perform very well at f/2 - f/2.8, and an f/2.8 lens could already be very sharp at f/4, etc etc etc
Agree with u bro, it's really like u can only find sweet spot of the lens when stopped down a little, which I wonder why is the case, probably it's manufacturing limitations.
So when we need to use at least F2, then we will have to get a F1.4 lens and if we need a good F4 or so, then minimum is to get a F2.8 lens.
However, some lenses actually are already working at it's best even at max aperture....which is why they are normally very expensive and high in demand...
By that logic, you'd *really* only be using the centre of the lens at f/22. Also, cropped-sensor cameras using a full-frame lens benefit from the sweet spot effect because of aperture rather than the imaging circle (it's not due to aperture btw).