E Liang,
reasonable alternative to gray filter would be rotating disk with shaped outcut
. Disk should be positioned between lamp and photoresist.
Regards,
Alex Pozdin,
Director of Engineering
5 Danuser Dr.
Hermann, MO 65041 USA
ph. 573-486-5500
e-mail: apozdin@laserusa.com
fax 573-486-5540