The Canon EF 50mm f/1.8 STM is a low-cost standard prime lens for full-frame Canon DSLRs; when used on an APS-C sensor camera, it covers an equivalent 80mm field of view. Extremely popular because of its normal focal length, bright, wide aperture and low price, the lens is small, light, and versatile. It boasts rounded aperture blades for pleasing out-of-focus details (bokeh), and special lens coatings to reduce flare and promote clear, contrasty images. It boasts several key improvements over its predecessor, the Canon 50mm f/1.8 II, including improved build coating, rounded aperture blades, a sturdy metal lens mount, full-time manual focusing, and a narrower f/22 minimum aperture. It's a great lens for everyday photography, and especially for low-light photography without flash. It is also optimized for shooting HD video. 

What you should know about this lens: 
• Bright aperture: Large f/1.8 aperture is great for low-light photography. Smooth, quiet AF with full-time manual focus: A gear-type STM stepping motor is useful for quiet and fast AF, and there's even a Movie Servo AF option for HD video. Full-time manual focus means you can override the AF function when the shutter is pressed halfway. 
• Better design: The focus ring has been moved so the lens can be designed smaller. A new rugged metal lensmount replaces the less durable plastic one on the older model. 
• Circular aperture: This lens delivers better bokeh thanks to its circular 7-blade aperture. This results in pleasing out-of-focus areas of the image and more natural-looking specular highlights.

One reason why the Canon 50mm f/1.8 is popular is because of its Sharp