It is a front mount wide angle lens so it will be attaching to the front of a regular slr lens with the filter threads. It is the filter threads on the front of the main lens that I am worried about breaking, not to mention any other sort of damage with that much weight hanging off the front.
In other words, I put my tamron 28-200mm on the camera and screw this 1.5lb wide converter to the tamron lens. I'm worried about breaking the filter threads on the front of the tamron. Likewise if I were to use it with an old manual focus 50mm, that weight would be on the front when focusing.
The wide angle is this lens here
Century | .7X HD Wide Angle Converter for Canon XL | 0VS-07CV-XL2
It is a bayonet mount but I have a similar smaller lens and it was easy enough to convert to filter threads. I'll post some pics in a bit.