Honestly, i've seen so many people rush into buying an 85mm and then they're just disappointed because they cant even use it in a normal sized living room. Its a great focal length for pro headshots but for a squirmy baby? Youre gonna want some room to breathe. Unfortunately, i had some real issues with the Viltrox AF 85mm f/1.8 II FE where it just wouldnt lock focus on eyes fast enough... really not as good as i expected for the price. If youre stuck inside, the 85mm is basically a telescope. Youll be backing up into the furniture constantly. Id strongly suggest looking at the Sony FE 50mm f/1.8 instead. Its the safer bet for a parent. I tried some of those super cheap alternatives like the Samyang AF 45mm f/1.8 FE but the build quality was a pretty big let down, felt way too plasticky and fragile. I worry about gear longevity when there are kids around, yknow? The 50mm is way more versatile for those cute full-body shots and you wont feel cramped. Just be aware the autofocus on the cheaper Sony 50 can be a bit noisy, which is annoying, but it's reliable enough for your budget. TL;DR: Stick with the Sony FE 50mm f/1.8. The 85mm is usually way too tight for indoor baby photos and you dont want gear thats gonna fail you when she starts crawling.

Honestly, 50mm is the sweet spot for babies. You dont want to be halfway across the house just to get a shot, and 85mm just feels way too cramped for crawling kids in my experience. I spent years testing primes, and for under 400 bucks, you really cant beat the value of the Sony FE 50mm f/1.8. It is compact, lightweight, and super sharp for the price. If you want something a bit smoother with better build quality, look for a used Sigma 56mm f/1.4 DC DN Contemporary. It is arguably the sharpest lens I have ever used on an APS-C body. Just remember that primes force you to move your feet instead of relying on a zoom, which actually makes you a better photographer long term anyway. Grab the 50mm and dont look back.

Subbing for updates

This thread is gold. Bookmarking for future reference 🔖

Building on the earlier suggestion, I think sticking to 50mm is the right move for your budget and the environment you described. Tracking a baby is already chaotic, so fighting with field of view in a tight room makes it harder. Here is my take on the options mentioned:

• Sony FE 50mm f/1.8: It is the ultimate budget winner. Definitely noisy and the AF can be a bit sluggish, but for stationary or slow-moving shots, it gets the job done and stays well under your 400 dollar cap.
• Viltrox AF 85mm f/1.8 II FE: Really sharp, but as others noted, the length is just awkward when you have limited indoor space. I have been satisfied with the 50mm on my crop sensor body for years. It works well and gives you that nice blurred background without needing to back into a wall. Honestly, save your money for extra batteries or a decent memory card since you will be taking thousands of pictures. You wont regret keeping it simple starting out.

To add to the point above about working space, I completely agree that 50mm makes the most sense indoors, but you do have a couple of solid alternatives within that $400 budget depending on your exact sensor size. After shooting with the Sony FE 50mm f/1.8 for over two years, I can confirm its sharpness is fantastic for the price, though the autofocus motor is definitely noisy and hunts in low light. If you are shooting on a crop sensor body instead of full-frame, you might want to look into the Sigma 30mm f/1.4 DC DN Contemporary as well. It gives you roughly a 45mm equivalent field of view, making indoor baby photography much easier while offering a slightly brighter aperture and much quieter stepping motor for focusing. Sticking with the 50mm focal length is definitely the right move for home environments, just keep your expectations realistic regarding autofocus speed on the cheapest first-party options.

Saw this earlier but just now responding. Before picking a lens, what camera body are you actually using? Whether you have a full frame or a crop sensor totally changes how those focal lengths work indoors. An 85mm is often way too tight if you dont have a massive living room. How much space are we talking about?