Filter factor

From Wikipedia, the free encyclopedia

In photography, filter factor refers to the multiplicative amount of light a filter blocks.

1 Converting between filter factors and stops
2 Filter factors for common filters
3 References
4 See also

[edit] Converting between filter factors and stops

The table below illustrates the relationship between filter factor, the amount of light that is allowed through the filter, and the number of stops this corresponds to.

Filter factor	Proportion of light transmitted	Number of stops
1	95-100%	0
1.3	75% (3/4)	1/3
1.4	70%	1/2
1.5	67% (2/3)	2/3
2	50% (1/2)	1
2.5	40% (2/5)	1 1/3
3	33% (1/3)	1 2/3
4	25% (1/4)	2
8	12.5% (1/8)	3

[edit] Filter factors for common filters

The table below gives approximate filter factors for a variety of common photographic filters.

Filter purpose	Wratten number	Other designation	Filter factor
Ultraviolet		UV(0)	1
Skylight	1A or 1B	KR1.5	1
Contrast filters
Yellow	8	K2	2
Yellow-green	11	X0	4
Orange	21	G	3
Red	25	25A	8
Green	58	X1	6
Colour conversion (blue)
3200 K to 5500 K	80A	KB15	4
3400 K to 5500 K	80B	KB12	3
3800 K to 5500 K	80C	KB6	2
Warming filters
3400 K to 3200 K	81A		1.4
3500 K to 3200 K	81B		1.4
3600 K to 3200 K	81C	KR3	1.4
3700 K to 3200 K	81D		1.5
3850 K to 3200 K	81EF	KR6	1.5
Cooling filters
3000 K to 3200 K	82A	KB1.5	1.3
2900 K to 3200 K	82B		1.5
2800 K to 3200 K	82C	KB3	1.5
Colour conversion (orange)
5500 K to 3400 K	85 / 85A	KR12	1.5
5500 K to 3200 K	85B	KR15	1.5
5500 K to 3800 K	85C		1.3
Neutral density
0.3	96	NDx2	2
0.6	96	NDx4	4
0.9	96	NDx8	8
Polarizers
Linear polariser		PL or LP	3 to 4
Circular polariser		PL-Cir or CP	3 to 4