Unfortunately, the native selection is still pretty bleak. If the Sport is too heavy, check out the Sigma 100-400mm f/5-6.3 DG DN OS Contemporary. It is way lighter for hiking and costs around 900 bucks. I had issues with AF speed, and it is not as good as expected in low light. Grab the Sigma TC-1411 1.4x Teleconverter too, otherwise 400mm is way too short for bears.

Ugh, I feel your pain so much. Honestly, the lack of native fast telephotos in the L-mount catalog has been driving me absolutely crazy for years. It is incredibly frustrating to have a body as good as the S5II but feel so limited when you want to shoot wildlife. I have vented about this exact issue to anyone who will listen. In my experience, if you want reliability without breaking your back or the bank before your Yellowstone trip, you should adapt Canon EF glass. I run the Sigma MC-21 Mount Converter EF-L with a used Canon EF 100-400mm f/4.5-5.6L IS II USM. You can grab the lens used for about 1400 bucks and the adapter is cheap. The autofocus is actually really snappy on the S5II with the phase detect, and it is much lighter than the Sigma Sport. Saved my back on long hikes, and the keeper rate is solid. Let me know if you want to know more about how that combo handles.

Man I wish I found this thread sooner. Would have saved me so much hassle.

I would suggest you be extremely careful with your selection given the specific AF requirements of the S5II. Honestly, you should just check out some of the detailed comparison spreadsheets on Reddit or search for L-mount telephoto shootout on YouTube. I saw a really thorough video about two weeks ago that compared every long zoom available for the mount, and it is probably the most reliable way to see the actual AF hunting behavior in real time. It is much safer to spend time researching those technical tests yourself than to risk a focus failure in Yellowstone. Just look for the top result under L-mount wildlife guide and you will find everything you need. Make sure to pay attention to the firmware versions they are testing, as that makes a huge difference for native vs third party glass.

This exact same issue has been on my mind for about six months now and it is honestly exhausting. As an experienced shooter, I still cannot find a lens that balances performance with portability for this mount.

• I would suggest being very careful about the weight of these long zooms because I have found they are just too heavy for long hikes and my back just wont take it anymore.
• You might want to consider that the autofocus hunting is a widespread issue; I am seeing it on all my non-native glass too.
• Make sure to be wary of the pricing because I havent found anything that feels like a good value lately. It would be nice to have an answer for you but I am stuck in the same position... I am worried there is no good solution right now tho.

Saw this earlier but just getting to it now. Unfortunately, the L-mount telephoto situation is pretty frustrating. If the Sport was too heavy, you definitely wont like the Sigma 60-600mm f/4.5-6.3 DG DN OS Sports because it is basically a heavy brick. I had issues with AF hunting on Sigma glass too, even with the phase detect on the S5II. It is just not as snappy as native glass. You should look at the Panasonic Lumix S 100-400mm f/4.0-6.3 OIS. Since it is a native lens, communication with the body is more reliable, and it weighs way less for hiking. If you need more reach, pair it with the Panasonic DMW-STC14 1.4x Teleconverter. Check the L-Mount Alliance compatibility charts on their site to see specific body AF benchmarks. It is not as good as expected for birds yet, but that 100-400 is the most professional middle ground for your trip.