First, let's talk about diffraction
Your 80D has a 26 MP sensor with pixels only 3.72µm wide. That figures out to a diffraction limited aperture (DLA) of f/6.0.
Diffraction Limited Aperture (DLA) is only applicable at 100% viewing size. This is because DLA assumes a Circle of Confusion (CoC) equal to the pixel pitch of a particular sensor. The effects of ...
I want to share my solution for the incompatible manual flash on canon new hot shoe mounting layout that seen on canon 4000d/1500d/etc.
First I bought a off ttl cord model: OC-E3 TTL and I short circuit the four wire into the x-sync contact and the camera recognize it as a manual flash and now I can use the Manual Flash