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85B vs. 85


Nick Norton

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1 000 000 :3400K = 294.1176 mired

1 000 000 :3200K = 312.5 mired

 

312.5 mired - 294.1176 = 18.3824 mired color temperature difference.

 

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1 000 000 : 5600K = 178.571429 mired

1 000 000 : 4800K = 208.3333 mired

 

208.3333 mired - 178.571429 mired = 29.761871 mired (color temp difference between general direct sunlight and idealized daylight ct balance)

 

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312.5 mired - 178.571429 = 133.928571 mired (color temperature difference between 3200K daylight balance and 5600K daylight balance)

 

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1 000 000 : 5400K = 185.185185 mired

 

185.185185 mired - 178.571429 mired (5600K)= 6.61376 mired

 

As you can see, a 200K difference is smaller and much less noticeable when compared between higher color temperatures.

thus the Mired degree is preferred in color temperature comparisons because then you can see how much actual visible difference there is in color temperature ( 18.3824 versus 6.61376 mired )

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as others mentioned it is also possible to shoot 500T tungsten balanced film in daylight without the 85 or 85B filter, rating it at about 320 ISO (thus exposing the red layer normally and overexposing the blue layer by about 2/3 of a stop) and then bringing the blue channel down in telecine about 2/3 of a stop. depending on the film there may be some blue contamination in the greens which can't be fully corrected afterwards and of course you have 2/3 stops of less headroom in the blue.

 

One thing to take into account is that if you shoot this way and UNDEREXPOSE the image you can't fully correct the shadows because there is no details left anymore in the reds. otherwise it is generally not big of a deal to correct it afterwards as long as you expose it correctly in the first place (expose it like you had the cc filter in place even if it isn't )

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it is also possible to shoot 500T tungsten balanced film in daylight without the 85 or 85B filter, rating it at about 320 ISO

If you shoot without the 85, you should use the stock at it's intended ISO. If you don't use the 85, you are already over-exposing the blue layer, so rating the stock at 320 ISO will increase that overexposure to 1+ 1/3 stop. That's enough for significant detail to be lost.

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