The magic of the EF 75-300mm

Finally managed to get a hold of my old 75-300. After using the STM lens for so long, the most obvious thing I noticed is the worse macro, thus I had to move way back and zoom in more to get a good shot.

But back to the topic. I'll try to explain this to the best of my knowledge, so here goes:

When I focus on a subject (let's say a toothbrush laying on top of a sink), then if we take 75mm FL for both with same settings, standing at the same distance, then the MK iii better isolates the subject. The STM lens will be sharp on subject, but other things will be sharp around it as well. However the Mk iii is sharp on the subject, but it isolates it much better. It's like what some people would refer to as "3D". Now before you yell at me saying IT'S APERTURE DUMMY! please note that I have a nifty fifty and used it for the sole purpose of isolation.

Anyways, I couldn't recreate the effect in PS no matter what. And yes I'm aware of the F4.0 vs F4.5, but still....... I tried to think maybe it has to do with the STM's superior macro capabilities or it's the IS (which turned out false as On and Off produced no difference at all in IQ) or the type of glasses the lens has..... so I'm starting to give up.

Go and take a picture (RAW) with a 350D at the lowest ISO settings, in daylight. Go into Photoshop and apply heavy sharpening. Now take a 750D and shoot the same subject with the same AP, ISO, daylight etc., but without touching Photoshop.

Now compare the end results side-by-side from a far distance. The 350D will have that WOW factor, and the 750D will seem a bit more soft. As you start to get closer you'll quickly realize that the tides have turned. The 350D is basically an oversharpened mess, while the 750D brings in more and more detail with each step. So the MK iii feels higher MP to me.

I guess that's the way I could best describe these two lenses. This wasn't intended to be an STM zoom lens bash, so I apologize if it looks like it. The 55-250 IS STM is brutal sharp, but the 75-300 seems to appear higher resolution, more detailed, and better isolates a subject, but it's quite soft an unusable over 200-250 mm. Let's not even mention the lack of IS. Does that make sense?