Bokeh underwater isn't really a thing (unless for macro with coloured backgrounds and strobes) so low light is the only benefit I can see of f1.4.This could be the missing lens in the Canon setup for underwater photography. I'm very interested in knowing what the minimum focus distance is.
Good ISO performance and denoise algorithms have basically nullified those constraints.
Are you thinking of using it for wide-angle macro eg laowa probes? Maybe the EF8-15/4 would be a current/cheaper option.
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