I made this for my Nikon lens.
You should choose different size of bottle for the size of your lens.
Is waterproofable with innertube.
Step 1: YOU NEED
_2 bottles of the same water (better if with flat bottom);
Step 2: CUT PLASTIC BOTTLES
cut the plastic bottles: one a tiny bit longer that your lens, the other 1 cm on top of were it start to become straight. (see photo)
Step 3: MAKE HOLES WITH SAFETY PIN
make holes with the safety pin all around the edge of the 2 pieces of bottles. 1/2 cm far apart.
Step 4: PUT ZIPPER
sew on zipper with dental floss (i used it 'couse is really strong), using the holes you made before with safety pin.
Step 5: CUT SPONGE
cut the spongy material: 2 circles of the circumference of your bottle and one rectangular piece that will fit the side part of your bottle.
Step 6: PLACE SPONGE
place the 2 circles on the bottom of the 2 bottles, and the rectangular piece all around the side. you can glue them to place (mine just hold themselves in place).
Step 7: DONE! WATERPROOF IT!
you are done! you can waterproof it if you want: cut an innertube in half and sew it like a ring of the size of your bottle circumference (it should be really tight fit) , place it all around the zipper (this will work only the side of your bottle are really flat, and if you make it tight...anyways I don't want to feel responsible for the safety of your lens!).