Unfortunately, I have had issues with the reliability of those cheaper third-party lenses during travel. The AF consistency is often not as good as expected when shooting candidly. Since you need something dependable for Tokyo, consider the Sigma 45mm f/2.8 DG DN Contemporary. The build quality is professional-grade and the autofocus tracking is much more stable than those other budget brands. Its a solid, reliable choice for under $400.

@Reply #1 - good point! That 50mm is a trap because people assume native is always faster, but that motor is ancient and clunky. Since you are heading to Tokyo, you really need to be careful with what you pack. Reliability is everything when you are halfway across the world and cant just swap gear if something fails. I would suggest looking at these specific options to stay under $400:

• Sigma 45mm f/2.8 DG DN Contemporary: This is my top pick for the A7C. The build is all metal and way more robust than the cheap plastic stuff. It is small, the AF is silent, and it fits the A7C aesthetic perfectly.
• Viltrox AF 35mm f/1.8 FE: If you need f1.8 for the bokeh, this is solid, but make sure to update the firmware immediately. I have seen some copies struggle with eye-tracking on newer Sony bodies until they get that patch.
• Sony FE 28mm f/2: A bit wider than you asked for, but it is a safe native choice for tracking reliability. Tbh, I would go with the Sigma. Just be aware f2.8 is a bit slower for night shots, so your ISO will jump. Whatever you buy, do not wait until the day before your flight. You need time to stress test the focus and check for decentered glass. Budget QC can be hit or miss... you dont want a lemon in Japan.

ngl switching to full frame is a trap for the wallet. I went through the same thing and unfortunately, the Sony FE 50mm f/1.8 was a massive disappointment for me. My trip to NYC was basically ruined by that lens because the AF motor was so slow and noisy it felt like using tech from 2010. Missed so many street shots because it just couldnt keep up with the A7C tracking. It was pretty frustrating. If you want something that wont ruin your Tokyo trip, here are two I actually kept:

• Samyang AF 35mm f/1.8 FE which is surprisingly fast and tiny.
• Viltrox AF 50mm f/1.8 FE for that classic focal length without the Sony motor lag. Honestly, dont touch the old Sony 50mm. Youre gonna regret it the second you try to snap a candid in Shinjuku. The Samyang is basically designed for the A7C and is way better for street stuff.

I totally feel your pain with the full frame transition... I made that same leap a year ago and my wallet is still recovering. When I took my A7C to Osaka last year, I was stressing about glass just like you are now. Ended up grabbing the Viltrox AF 35mm f/1.8 FE mostly because I couldnt justify the price of the Sony 35mm GM at the time. In my experience, Viltrox has really figured out the AF game lately. I was shooting quick street candids and it kept up with the A7C tracking surprisingly well. Its got a metal build that feels way more premium than the price tag, and that physical aperture ring is a lifesaver when you want to change settings on the fly without diving into menus. Itll be perfect for those neon nights in Shinjuku where you want that extra light. If you are worried about weight for those 20k-step days in Tokyo, definitely check out the Sigma 45mm f/2.8 DG DN Contemporary too. Its usually right around $350 or $400 and it is tiny. I have tried many lenses over the years, and while f2.8 sounds slow on paper, the rendering on that Sigma is just gorgeous... very classic look. Tbh, between those two, you really cant go wrong for street photography. The Viltrox is better if you really want that creamy background, but the Sigma makes the A7C feel like a pocket camera.

bump