Are you traveling to Japan on business or vacation? I asked because you will be carrying seven lenses. I am a photo enthusiast myself, have 35 mm film camera and done dark room work by myself. So I do not think anything unusual about carrying seven lenses on a trip.

If you are on a business and if you are a photographer, then I think there may be slightly bigger chance that at customs your items will be examined.

Regardless of the purpose of your trip, if you want to play it safe then bring receipts for camera equipment you will be carrying to Japan. Do you have receipts for insurance purpose? Receipts will prove that you have purchased items outside of Japan. Your stay at Japan is short, and taking all camera equipment with you when you leave Japan.

I say do not worry too much. 35 mm film camera I have did cost $2,000 - $3,000 total with lenses, flash, etc. I have carried those between the U.S. and Japan many times over past 20 or so years and never once I was asked to pay duty or show receipts. I have a dedicated silver stainless steel carry-on size suite case looking camera case, beside my carry-on bags to carry other personal items. May be once or twice I was asked what was in the stainless steel suite case, and opened to show the content. Never asked about the value and never asked about declaring at customs.

My feeling is if it is your personal items for personal use, then customs officers may not care. Movie and TV crews traveling for business to Japan will be carrying far more items with value far exceeding then that. I am not sure if those people were asked to pay duty every time they travel to Japan. My guess is they do not pay any duty.