how to correct Halogen light?greenspun.com : LUSENET : Large format photography : One Thread
hi, does anyone know how to correct Halogen light to 4500-5500K? any experience? and what filter to use? thanks
-- Jeff Liao (email@example.com), March 21, 2001
depending on whether you are dimming the light or what light modifier you are using, Halogens at full voltage are very reliably about 3200K. Do you want to filter the camera or the light to a 5500K balance? For a conversion filter on the camera an 80A converts 3200K light to 5500K, an 80B converts 3200K to 5300K, an 80C converts 3200K light to 4900K, and an 80D converts from 3200K to 4500K.
To filter a light source, use Rosco, Lee or Gamcolor 1/8th, 1/4, 1/2 or full CTB gels.
-- Ellis Vener (firstname.lastname@example.org), March 21, 2001.
This is a job for Mireds.
Mired is an abbreviation for 'micro reciprocal degrees': An artificial concept to turn non-linear colour temperature, measured in degrees Kelvin, into a (nearly) linear number.
The mired equivalent of a colour temperature is found by dividing it into 1 million. For example; daylight, with a colour temperature of 5500 K, has a mired value of (1000000/5500) = 181.8, call it 182.
You'll have to find out the colour temperature of your halogen lamps for sure, but my guess is 3400 K. This is a mired value of (1000000/3400) 294.
The beauty of mired values is that they can be added or subtracted, unlike colour temperatures. So, you need a correction of 182 (daylight mired value) minus 294 (3400K mired value) = -112. This is the mired shift of the commonly available 80B blue filter.
If you find that you need a mired shift that doesn't correspond to a readily available filter, then a specialist filter supplier, such as Lee Filters, will be able to supply mired shift filters for almost any lighting and film-type combination.
-- Pete Andrews (email@example.com), March 22, 2001.
There's a useful description here, in the "Take the lights temperature..." article.
At the end of the piece is a chart that I find very useful.
-- Struan Gray (firstname.lastname@example.org), March 22, 2001.
heliopan supplies their warming and cooling filters in decamired values and the filters are additive to make additional strengths.
No need for speciality filters. Schott glass, thin brass rims, fully coated, SH-PMC coating also available.
-- Bob Salomon (email@example.com), March 22, 2001.