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