For me, Mike Browne's YouTube videos, the free information he has on line at photography courses biz and the paid courses of his I have taken, have greatly increased my understanding of photography and lenses.  I can without hesitation say that you won't be wasting your time by checking out his videos and photography courses.  This video hit home with me when I first saw it. 

Video shared from the YouTube account of Mike Browne with the permission of Mike Browne.

When I first started paying attention to my photography I had a level of difficulty in getting my head around the effect of aperture on my photos and the concept of depth of field.  This was one of the videos of Mike's on YouTube that helped me understand a good bit better. I got a lot more from Mike's hands-on examples than listening to someone explaining a theory. I would encourage you to check out the many free videos Mike Brown has made available on his website and on YouTube.

Video shared from the YouTube account of Mike Browne with the permission of Mike Browne.