Discussion in 'Exposure Discussion' started by Sapphirephoenix2, Sep 14, 2011.

1. ### Sapphirephoenix2Member

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Dec 3, 2008
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Busan, Kr
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Hello, I am an experienced night photographer. With some issues.
I am doing a lot of things and trying to get some results that aren't happening right now.
I am shooting 4x5 film night landscapes and using flashlights, specifically a ledlenser light to paint my scene. I have not been able to produce an image with light painting right now. Any suggestions? or How to determine the duration of flashlight use when shooting for over 10 minute exposures?

-Dan
p.s. as you can see im not as experienced in light painting

2. ### Ian CMember

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If you use a light meter at the subject you can measure approximately how long the light needs to illuminate an area to give it normal exposure. That will at least give you a rough idea of how much light to use to record on film. Then you can experiment with film and evaluate the results to get an idea of how to proceed.

To get a reading on the meter you’ll need to measure the light fairly close to the source at a measured distance, say 1 meter from the light, and determine a basic exposure that will record on film.

Then for a light-to-subject distance D, the illumination difference (uncorrected for reciprocity) at the subject in f-stops based on a known 1-meter intensity is

Δf = 2*ln(D)/ln(2)

For example, at D = 2 meters,

Δf = 2*ln(2)/ln(2) = 2 stops less than the 1-meter intensity

At D = 5 meters,

Δf = 2*ln(5)/ln(2) = 4.6 stops less than the 1-meter intensity

Now you can determine the approximate light intensity at the subject.

Compensating for the considerable reciprocity loss can only be determined by experimentation. If you state your film and developer combination, possibly others who’ve done this with the same film and developer combination might offer advice with respect to the reciprocity compensation.

Other folks have had useful results painting with light using a hand-held sensor-auto flash like a Vivitar 283 using the “test” button to fire it. The photocell on the front of the flash (used within its range) stops the exposure when it receives the correct amount of light reflected from the subject. In this case no metering or calculation is needed.

Last edited by a moderator: Sep 14, 2011
3. ### Allen FridayMember

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I'm confused by your question. Are you making a 10 minute exposure which creates an image without light painting, and during that time you are using light painting to lighten objects that do not receive other light. Or, is the 10 minute figure arbitrary and all the light comes from light painting--if you don't light paint, the image basically comes out black?