ok so, to really understand if f/2.8 is worth it, you gotta look at how light transmission works when you zoom. With a variable aperture lens like the Sony E 18-135mm f/3.5-5.6 OSS, you lose about a stop and a half of light by the time you're at the long end. That basically forces ur ISO way up in low light, which can get pretty noisy on the a6400. I would suggest also looking at the Sigma 18-50mm f/2.8 DC DN Contemporary. It's super tiny—only 290g!—compared to the Tamron 17-70mm f/2.8 Di III-A VC RXD. If you dont need the extra reach or the Tamron's stabilization, the Sigma is actually a better travel pick imo. Just be careful tho, cuz the Sigma lacks built-in OSS. Itll be fine on ur a6700 with its IBIS, but might be a bit shaky on the a6400. Honestly, for the weight-to-performance ratio, that Sigma is hard to beat... gl!

Yo! Saw this earlier but just now responding... honestly I've been in your shoes and it's a tough call!! I once bought a huge, expensive lens for a trip and I literally regretted it by day two because it was soooo heavy and I was constantly worried about bumping it into things lol. For travel, I highkey think the Sony E 18-135mm f/3.5-5.6 OSS is the safe, practical choice for those bodies. It's such a fantastic value and way lighter for daily use! But if you're dead set on f/2.8, maybe look at the Sigma 18-50mm f/2.8 DC DN Contemporary for Sony E? It's AMAZINGLY small and way cheaper than the Tamron 17-70mm f/2.8 Di III-A VC RXD. Since your Sony a6700 has IBIS, you dont really need the lens stabilization as much, right? Basically, dont overspend on weight you'll end up leaving in the hotel room. Good luck!!

^ This. Also, I have been reading through everyone arguing about the 18-135 vs the Tamron, and honestly, both left me kinda bummed out after actually using them. I took that Tamron 17-70mm f/2.8 Di III-A VC RXD on a trip to Iceland last year and I actually hated how it handled on my a6700. It is just so front-heavy. Every time I looked at my photos, they were sharp sure, but my wrist was killing me by lunch. Then I tried the Sony E 16-55mm f/2.8 G and while the glass is incredible, the price tag and lack of OSS is just disappointing for most people. Basically, the thread is split between staying light with the Sony E 18-135mm f/3.5-5.6 OSS or going for the constant aperture. If you want my take, I actually ended up returning the big zooms and getting the Sigma 18-50mm f/2.8 DC DN Contemporary. It is tiny. Like, fits in a jacket pocket tiny. You lose the long end reach, but the portability actually makes you want to take the camera out. Quick tip: If you do go for a chunky lens, get a Peak Design Capture Clip to keep the weight on your backpack strap instead of your neck. TL;DR: The Tamron is a brick and the Sony 18-135 feels a bit mediocre in low light. The Sigma 18-50mm is the real winner for travel if you can sacrifice the zoom range.

Honestly, I once dragged a heavy full-frame kit through Tokyo and regretted every pound... basically, go with the Tamron 17-70mm f/2.8 Di III-A VC RXD. That f/2.8 constant aperture and built-in VC are 100% worth the 525g weight. The Sony E 18-135mm f/3.5-5.6 OSS is lighter, but it gets dark way too fast. Just be careful with the balance and make sure to check the size cuz it's chunky! gl

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