3 lens configuration confusion

[Billy F]

Greetings all,

I’m confused about the exposure setting relationship between the 3 lenses in conjunction with ASA /FC required in this scenario (Light Loss and depth of field aside).

My 3 lens (One stop down from wide open) and the foot candles required for 160 ASA (TRI X) as per Kodak’s specs are as follows:

CLOSE F4 125 F C
MEDIUM F2 32 F C
WIDE F2.8 64 FC

If the brightest part of my frame is 125 FC (As per meter reading) and I need close, wide and medium shots, do I set each of my three lenses to F4?

Or do I leave my lenses as C F4 - M F2 - W F2.8 and decrease/alter/shade the light source for my wide and medium shots OR filter my wide and medium lenses?

I hope someone can see the path of misdirection I went down in (mis)understanding the 3 lens exposure configuration and can straighten me out.

Thank You

[gianni1]

I never used foot candles, I think they were promoted by lighting companies and used by some in the film/photo industry. Sounds like a mathematical formula used by marketing executives to confuse and impress early consumers to purchasing product, like the terms "Multimedia PC", or "mega pixel".... FC has basis in physics and the fount of knowledge wikipedia, has a chart / look up table that says hypothetically:

F-STOP FOOT-CANDLES

2, 100
2.8, 200
4, 400
5.6, 800
8, 1600
11,3200
16,6400

To me that means, and I guess, you can ignore foot candles and use the f stop number instead???? Unless you have a light meter that measures in foot candles.

Gianni 8)

[Billy F]

Gianni,

Thanks for the response.

I don’t know who cooked up FC, or why, but as far as a means to express units of light goes, I guess it fit the bill, and yes, my Sekonic reads in it.

[gianni1]

Dug out my Sekonic Studio D, which has EV as a value from the exposure result, but no FC

That wiki page mentioned above, show Foot Candels is one of the measures of illuminance, others are the lux and EV (exposure value)

1 foot-candle = about 10.764 lux;
EV 0 roughly equals to 0.23 foot candle or 2.5 lux.

Makes some sense to me now. My confusion must have been because FC's not metric (which is a French).

Gianni 8)

[StoneBuilder]

Although this is pedantry worthy of Private Eye magazine (and off topic perhaps) an englishman named John Wilkins (qv http://en.wikipedia.org/wiki/John_Wilkins ) has an excellent claim to be the person who first devised the metric system. It's dreadful when someone else gets the due credit!

[Billy F]

No one here knows a Bolex well enough to explain it's 3 lens use?