Bryan at The-Digital-Picture has completed his full review of the Canon RF 14-35mm f/4L IS USM which was announced this past June and will begin shipping in limited quantities this month.
The first question on my comparison list was: How does the Canon RF 14-35mm F4 L IS USM Lens compare to the RF 15-35mm F2.8 L IS USM Lens?
… In the image quality comparison equalized at f/4, the two lenses are similar overall, with each having some advantages at specific focal lengths. The f/4 lens has dramatically stronger geometric distortion and has stronger lateral CA. The f/2.8 has stronger peripheral shading in most equalized comparisons.
… As I said at the beginning of the review, the RF 14-35's image quality is excellent (I'll get over the strong barrel distortion aspect), the Nano USM AF system is silent, high-speed, and accurate, and the L-series build quality promises to hold up to the rigors of constant use. Those features, along with the versatility that this lens provides, make the Canon RF 14-35mm F4 L IS USM Lens a great ultra-wide-angle zoom lens choice. Read the full Review