I designed and built a Canon EF Mount for my Game Boy Camera. The GBC has a sensor size of about 3.6mmÂ² which seems equivalent to a 1/4″ sensor. This gives the GBC a crop factor of about 10.81. With my 70-200 f4 mounted on a 1.4x extender, this gives me a max equivalent focal distance of about 200×1.4×10.81=3,026.8mm.
I always wanted a Game Boy Camera when I was a kid. It still looks like magic to me today.