I've just bit the bullet and splashed out on a 500mm f4 Nikkor, problem is it won't fit in my existing lowepro backpack. Can anyone advise what's the smallest back pack this lens might fit in. I need to get it on a plane as cabin baggage, i'm flying with Thomson next month and there a pain when it comes to cabin baggage hence the bag needs to be fairly light as the lens takes up most of weight allowance! The plan is to waddle through check in with my Domke waistcoat bulging and then repack the backpack when past the Gestapo at check in. Any advice greatly received, thanks