6.5mm f/3.5 Opteka Fisheye Lens. This is a great budget fisheye lens. Video shows the lens and sample pictures. This particular lens is for the Canon EOS sensor. Images taken with a cropped sensor. Full frame cameras would see noticeable vignetting with this lens. Shot with a Canon Rebel T4i. Product link below.
Product Link for Opteka Fisheye Lens: https://www.amazon.com/gp/product/B00KGE4VS2/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00KGE4VS2&linkCode=as2&tag=imagesbynatha-20&linkId=a0170e5200e68e84cfeb31ac2cf86c22