There are few things to accomplish when working with epoxy.
First of all not mixing all part 1 and part 2 but as much as you need.
Second , if you use marine grade epoxy , its hardener generally dark brown due to wait in the shelf. You must find crystal clear epoxy but very expensive.
Third , you must find pumps to pump one part epoxy to one part hardener equally or it doesnt set.
Fourth , you must find a well heated place or it fails.
Fifth , you must mix and set the drop in dust free environment.
Epoxy is not suitable for that experiment because it is expensive but acrylic is great , lots of military optics made from acrylic block cnc'ed
or rapid prototyped manufactured.
Why not built a real lens system for example peri from rapid prototyping. I am thinking that for years
All you need is a real lens design file , stl file and than apply to online rapid production companies , their web applet would give you a online quote from cnc file , you pay online and lens at your hand in a week.
Rapid prototyping firms produces car parts especially lamps , stops from clear or color acrylic but it is slow and expensive again.
Go , use your canon.

Umut