Please help me understand. If you don't intend to use this lens for video, is the STM really an advantage?
Not sure, but the reviews say it's quite quiet and very accurate and, though not a speed daemon, not annoyingly slow either. All in all, it sounds like a win, especially for something this cheap and small.
Also, why would you buy this lens and pay nearly twice the price for a slower lens than the 50mm f1.8?
Because it basically turns a 5D into everything I'd ever want in a mirrorless camera, something far superior to the Leica X2 / Fuji X100.
Are the optics better?
By all accounts, the Shorty McForty is optically on a par with, if not actually superior to, the 24-70. You're basically getting good L glass in a package that's the size of a body cap and cheaper than a good circular polarizer.
The 10mm difference is important for a small sensor camera?
I don't think 64mm equivalent field of view is a very interesting perspective. I'm very excited about the field of view on full frame...42mm is the textbook normal focal length for the 135 format, and 40mm is close enough to that as makes no difference.
difference? Better balance with a rebel body?
Again, no clue what this'll be like on those dinky little APS-C toys. To repeat, I see the Shorty McForty mounted to my 5DIII as a Leica X2 killer. As in, stomp all over, kill crush destroy, mop the floor with Leica X2 killer.
I find the 40mm focal length of marginal value over the 35mm.
I like 35 more than I like 50, but 35 does start to feel wide. I have a very strong hunch that I am going to very much like what the 40 feels like.
But I'll find out for sure this coming Wednesday....