Found this interesting video while YouTubing. Guy builds himself a f/0.4 lens and from what i can see, it works quite well. Not really practical but it would be fun to play with I believe that old Carl Z's f/0.7 $200,000 lens is the widest aperture lens right now and this one beats it out by quite a bit. Never the less, it is an interesting DIY project. 
https://www.youtube.com/watch?v=9cT0jXI7l4E![]()

