I went through this exact same dilemma when I got my R5 and honestly, the options are kind of frustrating. Picking up the Canon RF 85mm f/1.2L USM seemed like the right move, but unfortunately, it’s a total brick. Carrying that thing for a full session is exhausting, and the autofocus speed was honestly a bit of a letdown compared to the newer nano USM stuff. Its not as quick as youd expect for three grand tho. As for the Canon RF 135mm f/1.8L IS USM, I had issues using it for anything other than outdoor wide-open spaces. If your cousins session has any indoor components, youre gonna be backed into a corner constantly. The compression is nice, but its just not as good as expected for general use because its so restrictive... I found myself swapping it out way too often because the focal length is just too long for a single-lens setup. If youve got $2500, youre basically forced into the 85mm f1.2 for the versatility, even if it feels like a compromise on weight. Its the better choice for your situation, but just be ready for the bulk. The cheaper Canon RF 85mm f/2 Macro IS STM is definitely not the answer either; the motor is noisy and slow, which is pretty disappointing for modern mirrorless glass. Stick with the f1.2, but yeah, its not the perfect experience everyone says it is... dont expect it to be a magic bullet.

Building on the earlier suggestion, I’ve spent years chasing that perfect bokeh and I gotta tell ya... weight is a huge factor once you’re two hours into a session. > I worry itll be too long for the indoor shots I have planned You’re totally right to worry about that. My experience shooting an engagement party in a small bistro with a 135mm was a nightmare because I spent the whole night literally backed into corners just to frame a waist-up shot. If your indoor space is tight, the Canon RF 135mm f1.8L IS USM is gonna feel like a telescope. That thing is a technical masterpiece tho, especially with its 5.5 stops of internal stabilization. But the Canon RF 85mm f1.2L USM is the lens that actually makes people gasp when they see the files. Over the years I’ve noticed it has this specific micro-contrast that the 135mm doesnt quite replicate. For anyone on the fence about the cost, definitely check out the comparison tool on DPReview or look at the detailed technical breakdowns on the Digital Picture website. Pro tip: rent both for a weekend before you drop $2500. Renting is worth the small fee to see which one makes your R5 feel more balanced. If you really wanna save cash without losing too much quality, the Canon RF 85mm f2 Macro IS STM is a solid lightweight backup, tho it wont give you that f1.2 magic.

Regarding #1's point on weight, I agree. It's huge. I'm satisfied with the Canon RF 85mm f1.2L USM, but the Canon RF 135mm f1.8L IS USM is technically better for:

• Faster AF
• Better stability

Honestly, if you are doing an indoor engagement shoot, stay away from the 135mm. I have tried many lenses over the years, and the 135mm is just too tight for anything besides big halls or outdoor portraits. You are gonna be struggling to get half-body shots unless you are standing in another zip code. Since you want a single-lens setup, check out the Canon RF 85mm f2 Macro IS STM. It is tiny compared to the f1.2 monster, super sharp, and the focus is snappy. With the money you save, you could grab a Canon RF 35mm f1.8 Macro IS STM too. Having a wider lens for those cramped indoor moments is a lifesaver. You will thank me when your back doesn't hurt and you actually have room to compose your shots.