has this already been tried @sam?
sketchy?

this is a 3 stop ND gel from a rosco cinegel sample pack, they used to give these out for free.

i cut a circle and put it against the rear filter of the nikon 16mm. the canon 15mm has a square slot for gels, no UV glass filter, seems less sketch.

idk if i could see myself trying to handle a little plastic gel with dirty greasy fingers out in the streets, but maybe…
maybe if i wasn’t also handling a hass w/ fish at the same time.

i guess another factor would be whether f2.8 is too soft for the 16mm fish, maybe 1 or 2 stop ND would be better.

thoughts?

Yeah I already did this a few years back… I actually had a spare rear filter so changing in the streets wasn’t too much hassle. I ended up using it once or twice but in the end I just retired it, I’m not too fussed about shallow DOF on fish (I don’t really like using the 16 wider than f/5.6), and if you’re shooting in bright sun with flash (the only time you’d ever be beyond f/11), diffraction is the least of your worries.