Prime Canon RF 16mm F2.8 STM

Small, light & cheap, with surprisingly good image quality, the RF 16 f2.8 is an ideal lens for someone starting out with wide-angle.
The small size is off-set by needing heavy corrections in the corners, but the resulting image quality is still very good for a lens of this type & price.
Its size means its a lens that you can throw in your bag or jacket pocket and bring anywhere.
For the casual shooter who doesn't do a lot of wide angle, but wants the abilty to when needed, this is a very good option.
If ultimate image quality is your objective, then there are better option, albeit, much larger, heavier & more expensive.

I just took delivery of this terrific lense. I bought to try Astro, but found it great for landscape as well. I’m still struggling a little with focus in Astro, but the auto functions during daylight are perfect and accurate. I like the focus ring in manual, it’s smooth and accurate when in manual.
I’m not versed enough to say how well it works out on the periphery, but I’m satisfied with the images when shooting astro with most of the light centered in the image where my subject resides.

Just taken delivery of this, so just a first-impressions review at this stage.
This lens is almost identical in size to the RF 50mm f1.8 making it the joint-smallest Canon RF lens to date. For me, the whole point of mirrorless is to make it possible to create a smaller and lighter system than DSLRs with their big fat mirror-boxes. This lens epitomises that goal, and like the 50mm has quick and silent AF. I suspect it's also wider than 16mm as that appears to be the focal length after lens-corrections are applied. This is done in-camera for jpegs, so they have very low visible distortion. Raw shots however show significant pin-cushion and corner fall-off, and these need correcting if you're planning to use the lens for architecture, or anything with straight lines across the frame. However, without these corrections you also get a wider field of view than 16mm, and it's this extra subject-area that the cameras uses to allow for in-camera corrections. I've heard Canon also does this with the 24-240 which is I lens I've yet to try. So you have the choice of either a 16mm lens with very little distortion, or a wider lens (14 or 15mm probably, although not yet tested this) with significant pin-cushioning that you either live with or correct yourself.
At the asking price, this feels like a no-brainer.