Get the Nikon AF-S NIKKOR 85mm f/1.8G right now! Seriously, it is an absolute steal for the price and performs like a dream on the D850. I used one for years doing corporate headshots and the sharpness is just unreal. You can easily find one brand new for under $500, or grab a used one for around $300 and save some cash. The Sigma Art is fantastic too, but the Sigma 85mm f/1.4 DG HSM Art is way too heavy and will stretch your budget past $500 even used. The Nikon 85mm is super light, autofocus is snappy, and the bokeh is gorgeous. Go grab the Nikon, you wont regret it!

I transitioned from a DX body to the D850 a few years back for my portrait work. That 45MP sensor is a beast, but in my experience, it ruthlessly reveals any camera shake or minor lens flaws. I learned the hard way during my first corporate gig that high megapixels demand stabilization or much faster shutter speeds. Here are my main tips based on what worked for me:

• Prioritize optical stabilization. Handheld headshots on a D850 can get blurry fast if you drop below 1/160s without it.
• Check out macro lenses. They are often sharper than standard portrait primes and have virtually zero distortion. Instead of the usual suspects, I ended up using the Tamron SP 85mm f/1.8 Di VC USD. The VC stabilization is a lifesaver on the D850 sensor. Another killer option is the Nikon AF-S NIKKOR 105mm f/2.8G IF-ED VR Micro. The compression at 105mm is incredibly flattering for tight headshots, and it is insanely sharp. You can easily find both used under your $500 limit. Hit me up if you want to see some raw sample shots from either of these on the D850, I can send over some links!

Late to the party, but you might want to look at a used Tamron SP 85mm f/1.8 Di VC USD. With the D850, camera shake is a real issue and the built-in vibration compensation is a lifesaver. Just make sure to:

• Test the autofocus alignment right away.
• Buy from a site with a solid return window. Let me know if you need help finding a good place to buy one safely!