Unfortunately, youre gonna find that 800 bucks is a really tough spot for brand new wildlife gear. I have had issues with the price hikes lately and its honestly super frustrating for people just starting out. For what you want to do, the Tamron 150-500mm f/5-6.7 Di III VC VXD Fuji X Mount is really the only choice in their lineup that makes sense. That 17-70mm you mentioned is way too short... its more for like, family photos or vacation shots. For birds and deer, you absolutely need that 500mm reach. I have used it on my own Fuji and while the weight is a bit much at first, the image quality is solid. You might have to hunt for a used copy to stay under your budget tho. Dont feel bad about being confused, we all started there. Just dont waste money on the 17-70 for Yellowstone, you will just end up disappointed. Holler if you need help checking if a used listing is legit or anything.

> I have about 800 bucks saved up and I dont want to buy the wrong thing The 17-70 is for close stuff, you need the big numbers for wildlife. I looked at the MTF charts and thought the Tamron 70-300mm F/4.5-6.3 Di III RXD would be better, but I had issues with chromatic aberration on a trip to the coast. Unfortunately, under 800 bucks, you are stuck with compromises. It isnt as sharp as I expected, but it works for deer.