[onon359]

上下or左右高反差場合?
咁落左漸變減光鏡後測光,定先測光,才落漸變減光鏡?

[lokism3]

The filter is designed for panorama cameras (e.g. 617, 612 formats), because of the vignetting characteristic. You will find that the filter is grey dyed at the center and clear at the peripheral; the grey coloured area is equal to the effect of a ND filter, and normally -2EV. The photographer should meter as normal after putting on the filter, or do adjustment according to the stated ND value with a handheld light meter.

It seems that it is no use on the 135 format (conventional) DSLR, but if you want some special effect to show. The photo would look like either dark (under exposure) at center, or bright (over exposure) at peripheral.