[davidmanze]

I got marked down when doing physics at school as I thought about things in too much detail. I think I'm about to have one of those moments again!


I'd argue the focal length may be infinite for all practical uses, but it could be a bit less than that. If we assume the glass was perfectly parallel, it would still have mass. Mass means gravity, which would make the light converge at some point. However if we throw in dark energy that may not apply any more and things get way beyond my level!

 Hi,

    You shouldn't have got marked down!one should always ask questions and questions need details,I digress,I'm going to get out the bike this afternoon and check out this infinity theory:  I  may be sometime!