Filter factor
Encyclopedia
In photography
, filter factor refers to the multiplicative amount of light a filter blocks.
this corresponds to.
Filter factor = 2X
where the exponent "X" is the number of f-stop increases required.
An example: A deep red filter with a filter factor of 8
8 = 23
The normal exposure will be increased by three stops with this filter. As a consequence of this relationship, filter factors should be multiplied together when such filters are stacked, as opposed to stop adjustments, which should be added together.
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, filter factor refers to the multiplicative amount of light a filter blocks.
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 stopsF-number
In optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...
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 |
| 16 | 6.25% (1/16) | 4 |
Calculating exposure increase
The number of f-stops required to correct the exposure with a given filter may also be calculated using the formula:Filter factor = 2X
where the exponent "X" is the number of f-stop increases required.
An example: A deep red filter with a filter factor of 8
8 = 23
The normal exposure will be increased by three stops with this filter. As a consequence of this relationship, filter factors should be multiplied together when such filters are stacked, as opposed to stop adjustments, which should be added together.
Filter factors for common filters
The table below gives approximate filter factors for a variety of common photographic filters.| Filter purpose | Wratten number Wratten number Wratten numbers are a labeling system for optical filters, usually for photographic use comprising a number sometimes followed by a letter. The number denotes the color of the filter, but is arbitrary and does not encode any information ; letters increase with increasing strength.They are named for... | Other designation | Filter factor |
|---|---|---|---|
| Ultraviolet UV filter UV filters are individual compounds or mixtures to prevent ultraviolet light from getting through. UV filters are used in sunscreens to protect skin or in photography to reduce the level of ultraviolet light that strikes the recording medium.... |
UV(0) | 1 | |
| Skylight | 1A or 1B | KR1.5 | 1 |
| Contrast filters | |||
| Yellow | 8 | Y, K2, Y48, 022 | 2 |
| Yellow-green | 11 | X0 http://www.hoyafilter.com/products/hoya/cf-09.html | 4 |
| Orange | 21 | G | 3 |
| Light Red | 25 | 25A, 090 | 5 |
| Red | 29 | 091 | 8 |
| Green | 58 | X1 http://www.hoyafilter.com/products/hoya/cf-09.html | 6 |
| Infra-Red | 89B | R72 | 16 |
| 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 | A2 | 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 | B2, 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 | 1.6 |
| 5500 K to 3200 K | 85B | KR15 | 1.6 |
| 5500 K to 3800 K | 85C | 1.3 | |
| Neutral density Neutral density filter In photography and optics, a neutral density filter or ND filter can be a colorless or grey filter. An ideal neutral density filter reduces and/or modifies intensity of all wavelengths or colors of light equally, giving no changes in hue of color rendition.The purpose of standard photographic... |
|||
| 0.3 | 96 | NDx2 | 2 |
| 0.6 | 96 | NDx4 | 4 |
| 0.9 | 96 | NDx8 | 8 |
| Polarizer Polarizer A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined polarization. The common types of polarizers are linear polarizers and circular... s |
|||
| Linear polarizer | PL or LP | 3 to 4 | |
| Circular polarizer | PL-Cir, C-PL, CP | 3 to 4 | |
See also
- Filter (photography)
- Filter (optics)Filter (optics)Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....
- Wratten numberWratten numberWratten numbers are a labeling system for optical filters, usually for photographic use comprising a number sometimes followed by a letter. The number denotes the color of the filter, but is arbitrary and does not encode any information ; letters increase with increasing strength.They are named for...
- Exposure (photography)Exposure (photography)In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
- F-numberF-numberIn optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...