China vs USA Quality ZnSe Lens

[Dion]

I recently purchased some cheap "USA Quality" ZnSe lenses thinking I'd hit a bargain.

However, instead of a sharp focused beam like that of the "China Quality" it's just an unfocused mess that burns the workpiece to shreds.

The "USA Quality" lens is much lighter in colour and doesn't seem to have a sharp flat surface as the "China Quality" lens does.

It's almost like it has a slight concave surface where you'd expect the flat surface to be.

The convex surface doesn't seem to be any different between the two. It's the other (the surface aimed toward the workpiece) that isn't the same.

If you do a search on AliExpress for ZnSe lenses you'll see what I mean by USA and China quality.

Has anyone had the same or similar experience or have an explanation for this odd behaviour?

Thanks
Dion