I just got this Canon 90D because I want to take photos of my sister for her graduation next month but honestly looking at lenses is making my head spin. I tried reading about them online and people keep talking about millimeters and f-stops and I just dont get what any of it means. I have about 350 dollars saved up to buy one good lens that makes the background look all blurry and nice. Right now I just have the kit lens and it doesnt look pro enough.

• 50mm
• 85mm

I really just want her to look sharp and the trees behind her to be fuzzy. For a 90D what is the best portrait lens to get that look...