Congrats on the new camera! Honestly, for the price, you really cant beat the Sigma 105mm f/2.8 DG DN Macro Art. I went through this same dilemma and the Sigma just feels sharper when you're pixel peeping those 61MP files. The Sony FE 90mm f/2.8 Macro G OSS is great too, but its an older design and usually costs a few hundred bucks more. As for the focus stacking on the a7R V, the Sigma handles it just fine. I was worried it might be glitchy since its not native glass, but its been seamless for me. If you're looking for a budget alternative and dont mind manual focus, the Laowa 100mm f/2.8 2X Ultra Macro APO is also super sharp, but the Sigma is the better all-rounder for bugs and stuff where you need that AF.

I saw this thread and wanted to share my experience since I was in your shoes a few months back. I was honestly so nervous about spending even more money after dropping a fortune on the a7R V body. I really wanted to play it safe with the internal focus stacking feature because I heard third-party lenses can sometimes be finicky with firmware updates and I didnt want to risk any glitches with such an expensive camera. I ended up going with the Sony FE 50mm f/2.8 Macro mostly because it was budget-friendly and felt like a reliable, native starting point. My logic was that if I am gonna learn macro on a 61MP sensor, I should start with something manageable. One thing I learned pretty quickly is that 61MP is super unforgiving with camera shake. Because the 50mm is so much lighter than those big 100mm options, I felt way more stable shooting handheld while chasing bees around the garden. Practicality-wise, saving money on the lens meant I could actually afford a decent lighting setup like the Godox V860III-S TTL Flash and a good diffuser. Honestly, lighting is basically everything for macro work, especially when you are trying to keep your ISO low to preserve all that detail from the sensor. It might not be the most flashy choice, but it definitely helped me get my feet wet without the stress of a massive investment. Just keep in mind that with 50mm you have to get pretty close to your subjects, so maybe practice on slow-moving bugs first!

Gotta weigh in here because I love this setup! If you are focusing on reliability for that internal stacking on the R V, native glass is 100% the way to go. I have had zero glitches with Sony lenses whereas some of my buddies with third party stuff occasionally see weird focus skips during a burst.

• Sony FE 90mm f/2.8 Macro G OSS
• This thing is a total beast. It is super consistent and the focus clutch is amazing for switching back and forth when you are hunting bugs. Plus, the OSS plays nice with the camera's IBIS.
• Sony FE 50mm f/2.8 Macro
• It is way more budget friendly and super light. AF isnt the fastest ever, but it is very precise for stacking and great if you dont want to lug around a massive lens all day. I actually ended up missing my sisters birthday dinner last month because I found this insane iridescent beetle in the garden and spent two hours trying to get the perfect stack. My phone was blowing up in my pocket but I was just way too deep in the macro world... honestly I think she is still a little mad at me lol. But yeah, sticking to native glass is definitely the safest bet for that high-res sensor.

Honestly, if you want that internal focus stacking to work perfectly every single time, Id lean toward native Sony glass. A lot of people overlook the Sony FE 70-200mm f/4 Macro G OSS II for this kind of work, but it is actually incredible on the a7R V. It is super sharp and the AF motors are basically built for that high-speed stacking. You get 0.5x magnification natively, and if you add a teleconverter later, you can get 1:1. It handles the 61MP sensor way better than you might expect for a zoom. Another option if you are on a bit of a budget but still want that high-res detail is the Sony FE 50mm f/2.8 Macro. It is tiny and relatively cheap, but the glass is high quality. Just be careful with insects because the working distance is pretty tight. Tbh, for bugs, the extra reach on the 70-200 is a lifesaver even if it costs more.

Yo, been thinking about this and since everyone is talking about the usual suspects, you might wanna look at the Tamron 90mm f/2.8 Di III MACRO VXD. It is a much newer design than the Sony 90mm and handles that 61MP sensor like a champ. Plus it is way lighter than the Sigma 105mm, which is a lifesaver when you are stalking insects for hours. Tamrons VXD motors are legit for focus stacking... super quiet and fast. If you want to save some cash, the Sigma 70mm f/2.8 DG Macro Art is ridiculously sharp for the price. Like, scary sharp on the R V. Only catch is it has an extending barrel and the AF is a bit slower, which might make the internal stacking take a few seconds longer tho. Check out the reviews over at Phillip Reeve or Dustin Abbott for some real-world samples on high-res bodies. Really helped me decide when I was looking at macro glass... both these options are solid alternatives if you dont want to pay the Sony tax.