Using 2 ND filters stacked gave red colour

[hil26]

to the dead straw coloured grass.

To slow down the shutter speed I decided to stack to ND filters (Cokin ND8 and ND4 in the holder). Didn't get the result I was after (different story) but wondered why the red tone to the grass.


larger image

Any advise greatly appreciated

Dave

[ermintrude]

I've had this before using ND???1000 (not sure it was 1000, but something like that...) in that case I was told it was because with such a long exposure some ends of the spectrum are more able to enter through the filter than others (ie the red).

eg: