My ND3 has gone! Today I found out the reason that why there are unknown marks on my Herschel Wedge images since last solar observation in 25/5/2010. The marks on the image would not rotate with the camera. And I found there was no dust on the CCD, the filters and the Herschel Wedge. There were no visible damages in any optical parts. However, the problem was more pronounce in high magnification. Today I detach the ND3 and inspected it under the sun. Gosh! There were cracks on the ND3. I remembered that last time I reversed the order of assembling the Herschel Wedge. The ordering was:
Objective side, ND3, Herschel Wedge, Polarizer or Green continuum, Eyepiece side (WONG!!!)
This ordering terms out to be wrong. My ND3 cannot stand for the heat energy and micro cracks formed! I need to buy a new one now! Dear Herschel Wedge users, don’t repeat my silly fault. The correct ordering should be:
Objective side, Herschel Wedge, ND3, Polarizer or Green continuum, Eyepiece side (RIGHT!!!)
Cracks under strong light
No visible damage under normal light
Unknown marks on the image
Cracks under strong light 
No visible damage under normal light
Unknown marks on the image
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