The 81 series of filters control the bluish colouration that affects daylight film they can also remove excessive blue from the effects of electronic flash good for general scenics when the photographer wishes to remove the bluish cast from open shade or just add warmth to the photograph with an 81ef having the greatest effectthis filter combines the extreme warming capabilities of an 81ef with a neutral density 9 three stops filter the 81ef decreases colour temperature from 3850 3200