Pro Storm Jacket Camera Covers are the most compact and portable camera protection you can carry with you everywhere you go . . . so you wont hesitate to use it anytime the camera is going to get wet, dirty, or sit in the sun. They are perfect for live shots setups, locker room celebrations, shooting in rain, drizzle, snow, and dusty or dirty environments. They arent meant to replace heavy-duty covers and rain slickers costing hundreds of dollars when you really need that level of protection. Pro Storm Jackets can be slipped on and off in less than 5 seconds, which means youll actually use them when youd otherwise just let the camera get wet because you didnt want to struggle with a bulky cover. When youre done with it, just shake it off, stuff it back into its zippered case, and shove it in a pocket. The cover and case together only weigh about 2-5 ounces depending on the model. The Medium size (recommended for most customers) works well for short lenses up through 300-400mm f/2.8. Measure your camera/lens from the rear of the body to the front of the lens. If its 7"-15", this is the cover for you. The Large size is built for very long lenses. Measure your camera/lens from the rear of the body to the front of the lens. If its 14"-23", this is the cover for you...but, you might want to get a smaller size to go with it. The XL Xtra Large size is built for extra long len ses. Measure your camera/lens from the rear of the body