Olympus 25mm f/1.8

Does anyone use this lens for underwater photography? I don’t see much about it. I know there is a 30mm Macro but they seem to serve different purposes. 

I don’t see a use case for that lens underwater.  It’s not wide enough for reef shots, and not very useful for close up shots, and the wide aperture is generally not desirable unless shooting ambient light at shallow depths, but perhaps it’s OK for fish portraits, if anyone makes a port for it.  

For macro (extreme close up) the choices for m4/3 are 30, 45, 60, and 90 mm.  They differ in working distance and magnification.  I really like the 60mm lens.  

I actually have this lens and use it underwater but in hindsight it wasn't worth it. It is a good lens and for my fish portrait work it is good for mid-sized fish (angelfish, butterflyfish etc). However, the 12-50mm kit lens is just so much more versatile that the 25mm gets used very little. The original idea was to shoot it nearly wide open when there is very little ambient light, e.g. dusk, dawn or night, in hopes a video light would be adequate for both video and stills shooting. But I never go around doing that.

One good thing is that that all 3 my lenses; 60mm macro, 12-50mm kit zoom, and 25mm F1.8 fit in the same port for the 60mm macro lens. The 12-50mm zoom vignettes below 14mm but I don't need WA for my fish portraits. On my last trip I needed to document habitats for which I did need WA, even much wider than 12mm. I didn't like the idea of buying a dome port and ended up getting a AOI UWL-09F wide angle wet lens which worked much better than I anticipated.