This is a very nice addition to the Canon EF line-up.  Since my DSLR has an APS-C sensor, I needed a lens that would get me close to 50mm.  A cropped sensor makes this 40mm lens the equivalent of a 56mm.  I like the fact that the lens is very compact and light weight.  The optics are "Can-tastic".  The focus is great in auto mode or in manual and I very much like the option of switching back and forth.  I also purchased the Canon UV filter and the Canon lens hood.  The Canon 40mm f/2.8 STM has a very snug fit, but is easily and quickly swapped.  I have only had use of the lens for a week and have posted my very first photograph to this web page where other reviewers have posted sample photos.  I feel like this will be my "go to" lens for indoor family events like Thanksgiving and Christmas.  I am also planning to use it for a maternity shoot.  For the focal length and the money, this Canon EF 40mm f/2.8 is a great value.  No regrets. 

Question: How is the lens?
Answer: sensor , I needed a lens that would get me close to 50 mm