Filters can be either circular in a threaded mount to fit on the lens or be square and fit a "matte box" attachment.

Matte box/filters, square or oblong in the case of graduated filters:
come in various filter/matte sizes. The filter holder should be capable of rotating for mounting of dutch grads and polars)

Square filters:

6" Wratten (150mm x 150mm) (typical application Proffessional 35mm movie zoom lenses) see note 1

170mm x 130mm, Cokin X-PRO series Filters

4" Wratten (100mm x 100mm) (typical application Proffessional standard 35mm/S16 movie lenses, Cokin Z-pro series) see note 1

3 1/4" 84mm x 84mm eg Cokin/Tiffen P Series ("Proffessional"), Cromatek Matte Box or ProShade (typical application standard 35mm stills /digital movie lenses).

3" Wratten (75mm x 75mm) (typical application standard 16 movie and video lenses, largely superceeded by 84mm systems) also 76mm x 76mm, Hoyarex Filter System (stills filter system, using adapters to attach via the lens thread, similar to Cokin).

67mm x 67mm, Cokin A series ("amateur", though this is simply a size issue.... the upper limit of "A" series is recomended 62mm diameter lens thread (actually up to 82mm). Some circular 70mm filters eg Cokin Polars (actually a notched round filter, non threaded) fit this system.

2" (50mm x 50mm) somewhat rarer, usually behind or mid lens systems.

(note 1)
4" and 6" systems usualy require the matte box to be mounted on support bars attached to the camera or bridge plate.
Proffessional standards are (Arriflex) 15mm bars ("lightweight" centred 75mm apart, "Standard" centred 100mm apart) or 19mm bars.
The support bars" systems tend to be camera model specific, because of varying lens positions.
Adaptors to line up the lens for different cameras are called balancing plates.
eg there is a balacing plate for the XL1 to use an Arri 15mm bars, matte box and follow focus.

Cromatek Adaptor rings enable either the Matte Box or ProShade to be fitted to almost any lens. typically £12 (eg spaphoto.co.uk 2005)

Circular filters:
138mm (typical application Proffessional 35mm movie/HD zoom lenses) see note 1

Stepping Rings
Circular threaded ring that screws into front of lens to enable a smaller or larger threaded filter to fit.
Some Hasselblad lenses use a bayonet fitting for lens attachments.
Hasselblad Bayonet Fitting Stepping Rings, typically £12 (Kood, 2005)
Step Ring Hass (old-style Hasselblad bayonet fit) B50-52/55/58/67mm
Step Ring Hass (current type Hasselblad bayonet) B60-62/67mm
Step Ring Hass B70-77mm

 Lens Filters:

85s: W in front of 85 etc just indicates the name, Wratten, the original manufacturer. W85 is the same as W85A. Although often different manufacturers products will vary, even down to early glass filters having a green tinge.
The difference between an 85 and a 85B is about 1/8 CTB (see Colour temperature tables ) or a 81A.

Fluorescent light filters, remember, effects vary with different fluorescents:

Canon Filters Data Sheet (1980), Color Conversion Filters:
Skylight(Amber) 1.0x for Daylight Film-fair weather use
CCA4 (Amber) 1.5x for Daylight Film-cloudy conditions
CCA8 (Amber) 2.0x for Tungsten Film-morning or evening light
CCA12 (Amber) 2.0x for Tungsten Film-sunlight to obtain normal color tones
CCB4 (Blue) 1.5x for Daylight Film-morning or evening light to eleminate reddish tinge
CCB8 (Blue) 2.0x for Daylight Film-night or indoors using clear flashbulbs
CCB12 (Blue) 3.0x for Daylght Film-artifical light to obtain normal color tones

 

B & W filters and effects:

Neutral density filters, ND

ND
(Neutral Density) filters reduce the amount of light reaching the film. Useful in achiving a small depth of field in well lit conditions. They can be in front or behind the lens (the latter is often the case with video cameras or very wide lenses, where dust or marks on the filter would show up).

There are 2 notations (at least) for describing the light-stopping ability of ND filters
Hoya use ND2 (1 stop) ND4 (2 stop) and ND8 (3 stop)
Others use 0.3,0.6,0.9 and 1.2 for 1,2,3,4 stops (usually marked 3ND, 6ND, 9ND, 12ND etc)

Graduated NDs have an extra designation, hard or soft, refering to the edge of the transition to ND filter. some non movie makes are more vague, eg Cromatek Graduated Neutral Density Ref: NDGRAD is a 6ND soft.

Hint: you can use NDs on light meters too, to alter ranges or centre the needle

Imaging filters:

Diffusers, have a non-flat surface which refracts light randomly through the filter, softening and reducing image contrast.
Stars, have a grid of parallel scratches or lines which defract (bend) the light that passes between the lines, causing points of light to star as in so many old pop shows.
Nets, black nets are similar to star gratings, they hold back highlights and star point sources . They can also appear to polarise light. In addition white nets desaturate and coloureds colour shift.
Vari-burst, is a star filter verging on diffraction grating, splitting white highlights to a rainbow coloured star.
Fogs, cause highlights or the dominant colours to spread into the shadows. Heavy fogs veil the image. The effect is enhanced if the image is high contrast or has bright highlights.
Low contrast filters, use fine dust like dots to absorb light from the image. Highlights are affected more than shadows hence reducing contrast while focus is relatively unaffected.
Graduated filters are 1/2 or 1/3 coloured or neutral density fading to clear. Typically used to colour/darken skies without affecting foreground.
Polarisers, can block reflections from water or glass surfaces etc (or any polarised light source). A 'picture improver'.
There are two types of polarizing filter. Standard linear polarizers work only with older manual-focus cameras.
Newer circular polarizers have an additional thin sheet of material - quarter-wave - which lets the filter work properly with autofocus and newer auto-exposure cameras (These use the polarising effect from internal mirrors in order to work and so need unpolarised light to enter the lens).
Some people don’t like circular polarizers, as the visual effect is subtly different from linear polarizers. But if you have a newer SLR or AF video camera, you don’t have much choice.

 

references:
www.koodinternational.com/pages/filters.html
www.formatt.co.uk
http://www.tiffen.com
www.cokin.co.uk

Colour temperature tables:

Source (assume -10° K for each 1 volt drop in supply)	Kelvin	Mireds (1/Kelvin)
Domestic Tungsten	2900	345
Photographic incandescent or Halogen Tungsten	3200	312
Photoflood or 3200° source + 1/8 CTB	3400	294
3200° source + ¼ CTB	3600	278
3200° source + ½ CTB	4100	245
3200° source + full CTB	5550	182
Dawn or Dusk	2000	500
Sunrise + 1 hour	3500	285
Early morning and late afternoon	4500	230
UK Summer (!)	5500	180
Blue/white sky	6500	155
Light shade (summer) / overcast	7000	140
Typical shade (summer)	8000	125
Hazy sunlight	9000	110
Summer sky	30,000 +	33 -

 

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