Lack of sharpness at f1.8 on Canon 50mm STM

SD19194 wrote:

This only hit me the other day after reviewing many older photos and then doing a ton of practice shots. My Canon 50mm STM (newer model) simply isn't sharp at f1.8. So many times in the past I've gone down to this aperture hoping to get those crisp shots and have had to delete the photos thinking something must have went wrong whether it were camera shake or subject movement or the wrong shutter speed, etc. Now I'm starting to think I just have a rather lackluster lens that advertises f1.8 but really is best suited for f2.5 or 2.8. Has anyone ever heard anything with this lens with regards to this issue? Or is it at all possible I've been doing something wrong all along when going down to this aperture? It should be noted that when I go to 2.5 or bigger, things are almost always fine.

Also, the test shots I've done at f1.8 have been with a timer with the camera on a table to completely rule out hand shake. I also changed the AF point (red dots) to just one red dot in the middle for the test shots. Still, the photos lacked super sharpness in the middle.

This lens is a type that dates back sixty years to a time when fast lenses with their limited depth of field wide open were needed to focus precisely on a ground glass screen, but nobody expected to use an f/1.8 or /2 lens at a wider aperture than f/4.  That was the preserve of f/1.2 lenses that were a waste of money and not as good at apertures smaller than f/4.  (Telephoto lenses were another matter.) It's only the necessarily slower zooms of the last twenty years or so in conjunction with autofocus that have led us to use normal and wideangle lenses wide open.  Lenses like the Sigma Art and the fast L lenses are designed to be used wide open, but they're generally huge.