Honestly, been thinking about this and from a reliability perspective you really need to be careful with the Sigma 56mm mentioned above because that is technically a DC DN lens meant for crop sensors... so if you use it on a full frame body youre basically losing half your resolution and that seems like a pretty big technical drawback for a pro setup. Tbh I would go with the Sony FE 85mm f1.8 because it has much better weather sealing and a faster linear motor compared to the Sony FE 50mm f1.8 which feels a bit flimsy and the autofocus can be kind of noisy and hunt in low light which isnt great for reliability during a shoot. If you really want a third party value king that actually covers the full frame sensor you should look at the Viltrox AF 85mm f1.8 II FE because it is pretty well built and they keep releasing firmware updates to fix bugs. I am not totally sure about the exact MTF charts but they look decent enough for the price... check out these resources for the hard data:

• OpticalLimits for technical lens benchmarks
• Dustin Abbott for real world autofocus reliability tests
• SonyAlphaBlog for compatibility charts and sharpest aperture data Basically just make sure you dont accidentally buy an APS-C lens for your full frame camera because that happens way more often than you would think and it really compromises your gear!

Noted!

> is the 50mm a more versatile and affordable starting point? Do third-party lenses offer a compelling compromise between price and performance? Honestly, I have been digging into the spec sheets and market price history for a while now because I am also trying to pick my first real portrait setup. Before giving a final answer, I was wondering what kind of space you usually work in? If you are in a small home studio or indoors, that 85mm might actually be too tight for you, which makes the 50mm better by default maybe? From a market research perspective, if you want full frame glass on a budget, you should definately look past the Sigma DC DN series since those are for crop sensors like others mentioned. There are some realy interesting third party options that are built specifically for full frame and might offer more bang for your buck:

• Samyang AF 75mm f/1.8 FE is incredibly light and usually costs less than the Sony 85mm while giving a very similar compressed look.
• Viltrox AF 85mm f/1.8 II FE is built like a tank and the autofocus is actualy quite snappy for the price compared to the cheaper Sony 50mm.
• Samyang AF 45mm f/1.8 FE is a bit wider than a standard 50mm but the technical reviews say it is much sharper than the budget Sony 50mm f1.8. The Sony 50mm f1.8 is basically the cheapest way to get started, but the internal motor tech is kind of old and noisy. If you can stretch the budget just a tiny bit, those third party full frame primes seem to offer much better value per dollar. Not 100% sure yet but that seems to be what the data suggests!

For budget-conscious portrait photographers, the Sony 50mm f/1.8 offers versatility and affordability, making it an excellent starting point. However, the Sigma 56mm f/1.4 DC DN Contemporary provides superior sharpness and a faster aperture, delivering exceptional value for its price. While the Sony 85mm f/1.8 is a classic choice for portraits, it is more expensive and less versatile than the 50mm. Therefore, the Sigma 56mm f/1.4 stands out as a compelling compromise between price and performance.

Late to the party but totally agree with user_ba82b15d about the space issue... it is a dealbreaker if you are shooting in a small apartment. If you want the absolute best bang for your buck outside of the main Sony line, you gotta look at brands like Samyang and Viltrox. I have been using the Samyang AF 75mm f/1.8 FE for a while and it is honestly such a sleeper hit. It is much lighter and cheaper than the Sony 85mm but gives you that beautiful compression. The 75mm focal length is a nice middle ground too if you find 85mm a bit too tight. Another one to check is the Viltrox 85mm f/1.8 II AF Sony E. Its built like a tank compared to the Sony 50mm and the autofocus is surprisingly snappy on modern E-mount bodies. If you are on a tight budget, these third party options usually give you like 90 percent of the performance for half the cost, which is a win in my book.

FE 85mm f/1.8.