Filter factor

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

Contents

[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 the filter factors for a variety of common photographic filters.

Filter purpose Wratten number Cokin number Other designation Filter factor
Ultraviolet UV(0) 1
Skylight 1A or 1B 1
Warming filters
81A 026 1.4
81B 027 1.4
81C 027 1.5
Cooling filters
82A 023 1.3
82B 024 1.4
82C 025 1.5
Colour conversion (blue)
80A 020 2.4
80B 021 2
80C 022 1.9
Colour conversion (orange)
85 / 85A 029 2
85B 030 2.1
85C 031 1.8
Neutral density
(96) 152 NDx2 2
(96) 153 NDx4 4
(96) 154 NDx8 8
Polarisers
Linear polariser 160 PL or LP 3 to 4
Circular polariser 164 PL-Cir or CP 3 to 4
Contrast filters
Yellow #8 001 K2 2
Orange #21 002 G 2.5
Red #25 003 25A 8
Yellow-green 006 X0 1.5
Green 004 X1 4

[edit] References

  • Hoya Corporation, Filters for imaging
  • Cokin S.A., Cokin Creative Filter System


[edit] See also