Bryan Carnathan over at the-digital-picture.com just wrote a pretty decent 10-stop ND technical shootout-style review with the B+W ND vs. Heliopan ND vs. Hoya ProND vs. Tiffen ND vs. Singh-Ray Mor-Slo vs. Breakthrough Photography X3 ND.
http://www.the-digital-picture.com/Reviews/10-Stop-Neutral-Density-Filter.aspx
If you're concerned with critical sharpness and color neutrality definitely check it out.
Graham
ps - I'm with Breakthrough
http://www.the-digital-picture.com/Reviews/10-Stop-Neutral-Density-Filter.aspx
If you're concerned with critical sharpness and color neutrality definitely check it out.
Graham
ps - I'm with Breakthrough