I used a 15mm f2.8 for years, but the magnification is too high
for most work, and the field area is too small - I then went to the
cheap 10X biology magnifier (triplet, I think...), and lately to
an old Bausch and Lomb VERY sharp 6X(?) which has a wide field
and enough sharpness to make up for the lower magnification. I
use the lens cell without the "chimney" that came with it.