I agree neutral density filter would be the way to go.(posted 8192 days ago)If you want something slower, I might suggest APX100 or other grainy films processed in metol-ammonia developer. You could experiment with D-76 1+3 with additional ammonia solution from hardware stores. Why ammonia tends to enlarge grain? I don't know. (if you do the same thing with borax, you'll get a nice medium fine grain developer suitable for TMX)