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.

I think that what you are seeing is probably normal for that lens - it simply isn't sharp at f/1.8 and reaches it peak sharpness at f/5.6.

Have a look at the resolution table in the middle of this page from the review on Optical Limits: https://www.opticallimits.com/canon_eos_ff/905-canon_50_18stm?start=1

This isn't an unusual behaviour for a lens of this type. Even better quality lenses don't normally reach their sharpest point until 2-3 stops wide open. Reserve f/1.8 for when you really need it and then put up with the lower sharpness. Otherwise, shoot at narrower apertures. If you want a lens that is significantly sharper at f/1.8, then you are going to have to spend a lot more money for something like the Sigma Art 50mm f/1.4.