ALTA RCL is the large-size model (#3 in our range of 4) and is perfectly fitted to protect a DSLR with 150-600mm/200-500mm type lens attached.  
The Alta Rain Cover is a simple yet ingenious solution designed to protect a wide array of camera and lens setups without creating undue hassle or hindrance. When caught in a sudden downpour, pull the rain cover out of its pouch to protect your camera and lens. The intuitive design ensures no wasted time fumbling to get the cape onto your gear. This flat cover lands right on your camera and drapes around in seconds. Then, simply secure the hook-and-loop fastener around the lens, and the hook/loops underneath to prevent it from blowing away in a gust of wind. 
To fit the hook/loops, simply slip the hook on the elasticated cord under the tripod canopy (to ensure it doesn’t lift), then slip it through the first loop, and then hook onto the second loop. Alternatively, keep looping through until it is as tight as you need it to be.
Being an open ‘cover’ and not a closed sleeve cover, we ensure ease of use for all sizes of hands, as well as the possibility to use with gloves on. Most importantly, this design prevents condensation, so that we can promise you 100% clear viewing of screen, controls, and viewfinder through the transparent TPU window on the back.
The Alta Rain Covers have an incorporated accessory pocket under the rear viewing window and all come with a pouch, so you can fold it up neatly in any bag or pocket. Carry an Alta Rain Cover with you year-round, and never get caught off guard.