if you compare "wide opten" f/1.2 vs. f/1.8. IMO that wouldn't be fair
It’s as far as both lenses can go, I think it’s fair in the sense that none of them is having the advantage of being stopped down.
When I look at
TDP, my opinion is that at f/1.8 for both they are equal in the center (+some purple fringing), RF 45 much better in the midframe
I understand, but you’re probably not purchasing the 1.2 to shoot at 1.8, you’re buying the faster lens because you want a wider aperture

The 45, in my experience, always has better contrast, while the 50 has hazy corners in its widest apertures — my 50 is still a little hazy in the corners at 2.8, it’s only at f/4 that it becomes good.
On the other hand, the 45 can make some surfaces completely pink — that seems to mostly disappear in jpegs with DLO, but it’s visible in RAW files.
the 45 is WAY better up to f5.6 where the 50 catches up
I wanted to try the lens for my use case scenario, that’s why I decided to put it in my main camera instead of a R5 II, that I also had available. If I owned this lens, I wouldn’t stop it down beyond f/2 to f/2.8, perhaps f/4, since I have a higher grade zoom that features the same apertures. For that reason, I’m not interested in knowing how it performs, for instance, at f/5.6 or f/8.
They should cost same money
The 45 has a much wider aperture, is a wider angle lens, has a better motor (a newer version of gear type STM, that is smoother), and the build quality is similar to that of the 35mm f/1.8 (with poor-man’s internal focusing, which is nicer). Despite being softer, the 45 is a higher grade product from its roots. The 45 is similar to grabbing the 35 1.8 and sacrificing its IS and macro abilities, solely to have f/1.2, which is an extremely wide aperture and, as such, it’s a
very expensive attribute.
Probably the 45 does look much better on my R6 then the 33/45mpx sensors
It’s still not great at 20MP, honestly. It’s perfectly enough to produce good images viewed at “normal viewing sizes”, which is what most users do, specially with social media, and even in fullscreen on my 27” monitor (which I did) but, if you zoom in to 100%, you’ll see its weaknesses; if you don’t, you’ll probably be fine.
it's better then the 50 STM if you don't look in the corners, but not 2 to 3 times better as the price would suggest
At RRP, the 45 costs about twice the price of the 50 (249€ vs 539€ here, 10€ less than the 35), and allows us to drop ISO one entire f-stop.
Guys, do not underestimate how much more expensive having f/1.2 usually is. For many focal lengths, there’s a premium of 50 to 100%
over the price of a f/1.4 lens, not a f/1.8. This lens is not great, but it’s dirt cheap for what it is.
I’m inclined to purchase it next year, when the prices drop. It’s compact and extremely light, I could easily carry this in my shoulder bag, with the other lenses and both cameras.