BetterPhoto Q&A
Category: New Answers

Using a flash in sunlight

Just to clarify -

1. First scenario, is subject and background is in bright sunlight, shot around noon. Wanted slight fill flash for shadows, or perhaps I do not need a flash. Shot Tri-X 400. Couldn't fudge the F-Stop of shutter in order to get distance and sinc at 250. Metered using matrix for distance, using F100, SB-28, using fill flash. Photos came out underexposed, although color film came out fine, also at 400 Portra ND.)

Questions:

A. Should I even be using a flash?
B. If so, should I use flash compensation, or opening up one F stop on the lens?
C. Should I use a neutral density filter?
D. Should I use slower film?

I do not want the photos to appear as though a flash was even used, want a natural look, with light in the distance.

2. Scene 2: Morning light, subject was in open shade, distance was sunny.
Shot using central metering, metered with a grey card, and rated 400 film to 250.

A. Didn't use a flash, but background was blown out, subjects a bit underexposed. Should I have used a flash?

B. Flash compensation or opening up one F stop on the lens?

C. Slower film?

D. Neutral density filter?

Never used a netural density filter before, and not too much experience with the flash.

Hope this clarified my situations.

Thank you in advance,

Linda

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October 24, 2007

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November 16, 2007

When taking pictures of people we are reproducing a three dimensional object in a two dimensional media. Pictures of people are best if the lighting conveys an illusion of depth. We do this by skillful shadow placement (modeling). Additionally, people look best if the main light appears to come from above (midday sun). If our lighting is devoid of shadows it yields a flat uninteresting image. If we light using heavy shadow, the image will be too contrasy. We soften shadows cast by the main light source using a fill light. Since we always fill from the cameras prospective an on-the-camera flash is a suitable fill because of it’s location.

We need a way to adjust the fill intensity. If the fill light arrives at the subject plane too bright, it becomes the main and generally its placement is too low thus the lighting becomes substandard. If equal to the main, the result will be a lighting ratio that is technically known as 2:1 (considered flat). If the fill is one f/stop subordinate to the main the lighting ratio will be 3:1 (considered best for portraiture). If the fill is two stops subordinate to the main the lighting ratio will be 5:1 (considered contrastry). If the fill is three stops subordinate to the main the lighting ratio is 9:1 (very contrastry judged theatrical). Note: In a sunlit vista the sun is the main light source.

First you need to know the guide number of your flash unit. Guide numbers are published in the flash manual. Otherwise, setup a indoor test. Subject placed 10 feet from camera. Shoot a series at every f/stop. Have subject hold placard signifying f/stop used. Examine series, identify best exposure. Multiply f/stop used by 10. This is your unit’s guide number.

In a sunlight situation arrange subject and use your regular light meter (not flash meter) to set aperture and shutter speed. Use a shutter speed known to synchronize with the flash. Multiple f/number specified by 10. This value is camera to subject distance in feet that will cause flash illumination to arrive at the subject at an intensity exactly equal to the sunlight. Camera placed at this distance yields a 2:1 lighting ratio. For 3:1 ratio multiply distance in feet by 1.4. Retreat to this distance. Flash arrived one f/stop subordinate thus establishing a 3:1 ratio. Multiply again by 1.4 and backup to this distance, ratio is 5:1. Multiply by 14. again, backing to this distance yields a 9:1 ratio.

Too complicated? Nobody said it’s easy anyway, by now you know I only dispense technical gobbledygook of no particular value.

Alan Marcus
ammarcus@eathlink.net

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November 16, 2007

Thank goodness I sometimes review what I write. I made a serious mistake above. I thought about taking poison but since I have been wrong about 100,000 times or so, I decided to just print a correction, this time.

Multiple f/number specified by 10.

Should read:
Divide flash unit’s guide number by the f/number.

After all I am only human!
However I still dispense technical gobbledygook.

Alan Marcus

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November 16, 2007

OK Linda, I disagree with Haidar's response for a number of reasons. First measure your ambient light at whateer ISO you want to work at and get a reading locked in to the camera. Then, take a series of exposures two or three, bracketing the flash to go off at 1/2 stop increments LESS than your ambient light reading.

So, if you measured the ambient light to be at f 16., blast one at f 11.4 (1/2 stop under) Another at say f 11.0 and then a third at f8.5. The two stops that were suggested may not be sufficient to illuminate the eye sockets of your subjects and may look so natural as to be un-apparent. Outdoor flash needs a bit of punch but not so much as to overpower the daylight.

Experiment with it and dial it in based on your particular flash unit. Play around with the numbers Alan suggested and see which ones give you the most pleasing results. BTW, you're going to notice a big difference between bright sunlight, say out on a beach and more diffuse sunlight, say a bright overcast day.

My rule of thumb is to use 1/2 to 3/4 of an f-stop under ambient light, no matter what ISO I'm working at.
Take it ummmmmmmmmmmm light ;>)
Mark

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November 16, 2007

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November 18, 2007