Totally agree! The Sigma 28-70mm f/2.8 DG DN Contemporary is technically safer for low light than the Sony FE 20-70mm f/4 G. It’s lightweight, reliable, and honestly i'm very satisfied with the results! 👍

I was worried about fatigue, so I basically got the Sigma 28-70mm f/2.8 DG DN Contemporary for Sony E! It's fantastic. Lesson: dont risk injury, go light, right??

Sooo I went through this exact same headache last year. Honestly, I started with the Sony FE 20-70mm f/4 G because that 20mm wide end sounds amazing on paper. But unfortunately, it was kinda a letdown for me during actual use. I took it to a family wedding and some indoor spots, and man, that f/4 aperture was just not as good as expected in low light. I had to push my ISO way too high and the results felt a bit "meh" for the price I paid. It was super disappointing because the lens is so sharp, but the light gathering just felt weak for a do-it-all zoom.

I eventually swapped it for the Sigma 28-70mm f/2.8 DG DN Contemporary for Sony E and honestly, it felt like a massive weight off my shoulders (and my wallet). From a cost-conscious perspective, the Sigma is such a better value. It’s light enough that it doesnt feel awkward on the a7C II body, and that f/2.8 is literally a lifesaver for family shots where kids are moving around in dim rooms.

I also briefly tried the Tamron 28-75mm f/2.8 Di III VXD G2 for Sony E, which is a beast, but it felt a bit too front-heavy on the smaller body compared to the Sigma. If you really need that 20mm, the Sony G is cool, but for everyday travel, I found the f/2.8 trade-off way more useful than the extra width. Had issues with the f/4 just feeling too slow for the premium price... anyway, thats just my journey with it. gl with whatever you pick! 👍

Honestly I've spent wayyy too much time digging into the technical specs and market trends for these compact zooms lately. From a market research standpoint, it’s really interesting how brands are carving out different niches for the C-series bodies. I was in a similar spot and realized that the Sony FE 24-50mm f/2.8 G is basically the industry’s response to this exact dilemma—it’s super light and compact but keeps that f/2.8 speed that everyone misses on the 20-70mm. I also did some deep dives into the Tamron 28-75mm f/2.8 Di III VXD G2 and the autofocus is techincally a step up for tracking fast-moving subjects compared to some older designs. Quick tip: check the lens motor specs—VXD or XD linear motors are a must for the a7 IV's AF system to realy shine. If you can sacrifice a bit of reach for the weight savings, that 24-50mm is a total sleeper hit for travel and family stuff without the f/4 low-light penalty.

Honestly, if you are bouncing between the a7 IV and that compact a7C II, you should really take a look at the Tamron 20-40mm f/2.8 Di III VXD. It is kind of a sleeper hit for this exact dilemma. You mentioned liking the 20mm width of the Sony f/4 but wanting the f/2.8 speed for low light and family stuff... this lens basically gives you both. Most people get stuck thinking they need to reach 70mm, but for a daily carry, having that 20mm ultra-wide end is a total game changer for indoor shots or travel architecture. Since it stays at f/2.8, you dont have to crank your ISO as high as you would with the Sony FE 20-70mm f/4 G. Weight-wise, it is only about 365g, so it wont feel front-heavy on the smaller a7C II body at all. Tamron has really nailed the balance between size and sharpness lately. If you find yourself needing more reach, you can always use the APS-C crop mode on your a7 IV to get a bit closer, but for a walk-around lens that handles low light and tight spaces, this is the one i would grab.

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