Honestly, if you want peace of mind, just grab the Sony E 18-135mm f/3.5-5.6 OSS. I have used it for years and it is way sharper than the 55-210mm. The build is solid enough to survive a Japan trip without breaking the bank. The Tamron is fine, but sticking to native glass usually keeps focus issues away. You dont want gear failure when you are overseas, trust me.

Honestly, skip the Sony E 55-210mm f/4.5-6.3 OSS. It feels super cheap and the range is just okay for travel. If you want to go to Japan and not swap lenses constantly, you might want to consider the Tamron 18-200mm f/3.5-6.3 Di III VC. It covers way more ground.

• Tamron is much more versatile for street shots
• Sony one feels flimsy in the hand Be careful with the sharpness tho, both are budget zooms so dont expect prime lens quality. If you really care about sharpness, you might want to consider saving up for a Sony E 18-135mm f/3.5-5.6 OSS. It hits a sweet spot between size and image quality that the cheaper ones just cant touch. Dont stress too much, just bring extra batteries!

> You should look at the Sony E 18-135mm F3.5-5.6 OSS instead if you can find it used. Building on the earlier suggestion, the Sony E 18-135mm f/3.5-5.6 OSS really is the king of travel zooms for the A6400. It balances size and reach way better than the Tamron 18-200mm f/3.5-6.3 Di III VC, which is pretty chunky by comparison. I've used the Sony E 55-210mm f/4.5-6.3 OSS before and it's fine for bright days, but the contrast just isn't there. Actually, speaking of Japan, if you have any extra room in your bag, bring a decent pair of noise-canceling headphones for the flight. I picked up some Sony WH-1000XM5 recently and they honestly saved my life on a long haul last month. Being able to actually sleep on a plane is a game changer for travel. Anyway, but yeah, definitely stick with the 18-135mm if you can find a good deal.

To add to the point above: having used both, honestly, the Sony E 55-210mm F4.5-6.3 OSS is just too limiting for travel. I missed so many shots in Kyoto because I couldn't go wide enough. You should look at the Sony E 18-135mm F3.5-5.6 OSS instead if you can find it used. It hits that sweet spot for sharpness and size that the others kinda miss tbh.

Been thinking about your question for a few hours now and honestly, I am in the exact same boat. Planning a trip is already stressful enough without second guessing every piece of glass in your bag. I am still sitting here staring at my cart for my upcoming trip trying to decide if the weight saving is worth the potential sharpness trade-offs. Not sure if I want to commit to one lens or just suck it up and carry a couple of primes. It is a tough call and I am honestly just as lost as you are right now. I keep hearing mixed things about reliability when you are walking around for twelve hours a day. Whatever you end up choosing, just make sure you test it out on the streets before you board that flight. I have heard horror stories about gear acting up at the worst possible time so maybe just stick to what feels most solid in your hands.