A bunch of different sizes to checkout and buy on Amazon
These little hoods are a great little addition to your camera bag if you don't need a full matte box for your shoot. They have 3 stages: Flat for storage/Open a bit/Open a lot.
Why do you need to block sharp light from hitting your lens?
Flares can look cool if thought out and done right, but many many times a flare can just ruin a shot, and you want to be able to control it. Notice how pretty much all photo lenses come with some sort of lens hood? Yep, that's for flares. So, if you've either lost the original, have a lens that didn't come with one, or want one that can screw on so it works with several lenses instead of one, this one works a treat.
It packs down which makes it more potable than typical rigid lens hoods, and if you buy a larger size, you can get step up rings to mount it to smaller threaded lenses.
It's round, and since frames are rectangle, you might get the corner of your frame clipped by the hood, but that's where those three stages come in handy, if it clips the frame, collapse it down to the next stage. I have found with very wide angle lenses it needs the short stage which doesn't do much anyways. Since these things are so cheap, here's a quick fix for that: Take a sharp scissor, and cut out small notches for each edge of the frame. Use one of your existing lens hoods as a guide to see how they make such cutouts to avoid edge clipping.