Oh, I now I understand... I thought that you mean the lens, now I realised that it's the hole itself you're speaking about... Sorry, my mistake...
Ok, so how to make the hole in cube... I've seen a topic about this a few days ago in General Anim8or Forum; it's a lot of work in Point Edit mode...
Anyway, boolean substraction is probably the easiest way (although it doesn't always work as you want...). My suggestion is to lathe an object (kind of cylinder) exactly in the shape of the hole and use this object for boolean substraction instead of cylinder; you can also use a cylinder with more longitudes (if you doubleclick a cylinder, you can edit number of longitudes/latitudes...)