"A Few Things That You Should Know"
1. Filters are made from three types of material: optical-quality glass, gelatin film (gels), and rigid plastic resin.
2. Available glass filters: gel filters laminated between glass, solid glass dyed in the mass filters, and Tiffen laminated filters in which two pieces of optical glass are laminated together and the filter's color is an integral part of the bonding material.
3. Types of filters: direct screw in, series size (mounted filter in an unthreaded filter ring - filter is sandwiched between a filter adapter ring that screws into a lens and a retaining ring), drop in filters that are held in place via a filter holder.
4. White light is a combination of all the colors of the spectrum.
5. A filter transmits light of its own and similar colors. Depending on the filter's density, it blocks some or most of the other colors.
6. Objects that reflect all combined colors appear white.
7. If an object reflects only some colors, that object appears colored.
8. If an object reflects none of the colors, the object appears black.
9. Primary colors = red, blue, green (also known as additive colors)
10. Secondary colors = yellow (red & green), cyan (green & blue), and magenta (red & blue) (also known as subtractive colors)
11. A filter lightens its own color in black & white photography and darkens its opposite.
12. A spectral curve graphs the percentage of light transmission of a filter.
13. The filter factor indicates the required exposure increase required as a result of light being absorbed by the filter.
14. The filter factor depends on the light source and film type in addition to the absorption of the filter.
15. Average sunlight is rated at 5,500-Kelvin temperature.
16. Household tungsten lighting is rated at 2,700 - 3,200 Kelvin.
17. Color conversion - (80 & 85) and light balancing filters (81 & 82) change the Kelvin temperature of the light reaching the film. (raise or lower the temperature)