One reason why my 600mm f4 is gathering dust

Just brought the Panasonic 100-300mm out for a test run.  I felt that optically it's around 60 to 70% of the 600 f4 but at least I don't have to lug around 10lbs for the lens and an additional 5 lbs for the tripod and wimberly head.  IQ wise it's more than an acceptable trade off for the small size.  It's not the best for sure but for travel it's a welcome addition.