In my experience, the Sigma 18-50mm f/2.8 DC DN Contemporary for Sony E is ur best bet cuz that f/2.8 is SO clutch... basically its tiny too! gl

Stumbled upon this discussion and honestly, I have gotta chime in with a slightly different take. I spent about three years shooting street in Chicago with the a6400, and I've gone through just about every zoom lens in the E-mount lineup trying to find that perfect balance. Respectfully, I'd consider another option besides the ones mentioned. While the Sigma is tiny and the Sony 18-135 has the range, there is a massive factor your overlooking: the a6400 doesnt have IBIS (In-Body Image Stabilization). When I used the Sigma 18-50mm f/2.8 DC DN Contemporary for Sony E, I loved the size, but I lost so many shots to micro-jitter because the lens lacks stabilization too. It was seriously frustrating for those candid moments you mentioned. My go-to for the last few years has actually been the Tamron 17-70mm f/2.8 Di III-A VC RXD. Here is why it wins for street:

• It has VC (Vibration Compensation) which is a lifesaver on the a6400 body.
• You get that constant f/2.8 for low light and nice subject separation.
• The extra 20mm on the long end (70mm vs 50mm) makes a huge difference for candid portraits without being as bulky as the 18-135.
• It's sharp edge-to-edge, basically rivaling the much pricier Sony E 16-55mm f/2.8 G. It is definitely bigger than the Sigma, but its not 'heavy' per se. I mean, you can still carry it all day on a neck strap without your neck screaming at you lol. If youre looking for the best value and performance, especially without IBIS, the Tamron is the way to go. It just works better for those quick, handheld moments where you cant afford any blur. Good luck with the choice!!

👆 this

Just saw this thread and honestly you guys covered the big trade-offs well. Between the Sigma being tiny and the Sony having that crazy reach, it basically comes down to your shooting style. Arthur made a great point about the lack of stabilization on the a6400 too. One thing I really want to caution you about though is the weight balance and overall reliability for street work. Its easy to get sucked into looking at specs, but if you get a lens that is too heavy or front-heavy, the a6400 becomes super uncomfortable to hold for more than an hour. I learned that the hard way. Also, be careful with lenses that dont have some sort of weather sealing. If you are doing street photography, you are gonna get caught in the rain eventually, and having a lens that feels flimsy or lets dust in will just end up costing you more in the long run. Focus on something that feels solid in the hand. If it feels like cheap plastic, it probably wont survive a busy city environment for long.

Noted!

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Yep, this is the way