As far as optical quality goes, focusing only on f-stops is like focusing on horsepower for cars. Even in f-stops, not all f-stops are equal since some lens tra

As far as optical quality goes, focusing only on f-stops is like focusing on horsepower for cars. Even in f-stops, not all f-stops are equal since some lens transmit more light than others at the same f-stop. This is called t-stops and is used a lot of in pro video lenses. Another example is if I focus on something and then zoom in and out some lenses have to refocus and others maintain focus. This is an important feature for video and any kind of fast shooting. Many lenses have much more "focus breathing" than others. That is, the change of the effective focal lens as the lens focuses closer and closer. I had a lens that was 200mm but it was really only at infinity. At close focus is was closer to 135mm since the focus breathing was so pronounced. Bokeh, chromatic/comatic abberations, geometric distortion are other things I can go on and on about.