Dear Dr.Vik, Dr.Mathioudakis, > When we align/focus the instrument in the lab, we do it using the SDSS u', > g' and r' filters which you made for us. If we then want to use a > different filter, it must have the same optical thickness as the filter it > is to replace in ULTRACAM. Hence, the new narrow-band 350nm filter that > you are making for Mihalis must have the same optical thickness as the u' > filter that you made for us. We did the final check about each mechanical thickness in consideration of the comment by Dr.Vik. The recipe of new filter is, BP*Fused Silica(1.25mm) + U-340(2.50mm) + (LWP)*Fused Silica(1.25mm)*SWP Thanks, Toshihiko