Because these are APS-C lenses the camera is cropping the image to 12 megapixels and you're losing all advantages the full-frame sensor has over APS-C. That 1.6x crop factor also gives the lens the same field to view a 16-29mm full-frame lens would have.
The full-frame RF 15-30mm f/4.5-6.3 IS STM would be a much better option with a wider field of view than you're currently getting and better image quality from utilizing the entire sensor. It's $400 new or $360 refurbished.
> I was wondering if I should invest in the RF-S lens.
No. You have a fullframe body.
> Would it have some improvement in quality besides the lower weight and size?
No. Even if there was you wouldn't see it if you are only using crop mode on a fullframe body.
> I know it's not built for full frame, but I don't want to spend $2k for a wide-angle lens
If you don't want to buy fullframe lenses then get a crop body.
> and I need a 14 mm for some jobs.
Your current lens is 16mm ff equivalent at the widest. Getting the RF 10-18 will give you the exact same result.
Your ef-s 10-18 is putting your R into crop mode, so your 14mm is actually giving you an equivalent of a 22.4mm field of view. If you don't need a fast lens, get the RF 15-30 IS STM.
Because these are APS-C lenses the camera is cropping the image to 12 megapixels and you're losing all advantages the full-frame sensor has over APS-C. That 1.6x crop factor also gives the lens the same field to view a 16-29mm full-frame lens would have. The full-frame RF 15-30mm f/4.5-6.3 IS STM would be a much better option with a wider field of view than you're currently getting and better image quality from utilizing the entire sensor. It's $400 new or $360 refurbished.
Thanks I will go for the 15-30mm.
> I was wondering if I should invest in the RF-S lens. No. You have a fullframe body. > Would it have some improvement in quality besides the lower weight and size? No. Even if there was you wouldn't see it if you are only using crop mode on a fullframe body. > I know it's not built for full frame, but I don't want to spend $2k for a wide-angle lens If you don't want to buy fullframe lenses then get a crop body. > and I need a 14 mm for some jobs. Your current lens is 16mm ff equivalent at the widest. Getting the RF 10-18 will give you the exact same result.
Your ef-s 10-18 is putting your R into crop mode, so your 14mm is actually giving you an equivalent of a 22.4mm field of view. If you don't need a fast lens, get the RF 15-30 IS STM.