Flash Photography

by Paul Blixt
Rev. 9/221/01
A. The nice thing about strobe lighting is:
...You have an extremely brilliant light which permits the use of small apertures resulting in more depth of field.
...Very short light duration which prevents camera and subject movement.
...The color spectrum nearly balances daylight.
B. Accurate exposure is important. Make the following test if you are not sure of your personal guide number:
... Position your flash on camera 10 feet from a subject in an environment typical of your photos.
... Make sure of the speed of the film in your camera.
... Check your camera manual to determine the fastest shutter speed recommended to obtain a full frame exposure.
... Shoot 5 exposures, starting at f 22 to and including f 5.6
... After processing the film select the best exposure. This f stop times 10 feet produces your guide number.
...To take pictures, divide your guide number by the distance to your subject to obtain the correct exposure. (i.e. #110 divided by 5 feet = f.22
...To compute a new guide number for a slower or faster film:
........ASA 100 to 50 = 110 times .7 = 80 ,
........ASA 110 = 200 = 110 times 1.4 = 160
........ASA 100 to 400 = 110 times 2 = 220
C. Be sure you have a full charge in rechargeable batteries or fresh alkaline batteries in your flash unit.
...Wait for the ready light on flash. Not waiting could re-result in underexposed films.
D. Reform you capacitors if you haven't used the flash for several weeks.
...Turn on flash and wait for the "ready" light.
...Wait an additional 15 to 20 seconds -- then fire the flash, using the "open flash" button or shutter release. (no film in camera preferred. )
...Repeat these steps 4 or 5 times to be sure of full flash exposures when you start shooting pictures.
E. Consider the room or area you are shooting in.
...Close your lens down one stop when shooting baby in bath tub. Open you lens one or more stops if the room is large and has a high ceiling, dark rug and furniture.
F. Bounce flash produces a beautiful soft lighting.
...Be sure to observe the color of the wall or ceiling you are using as a reflector.
...The 45 or 60 degree angle on my Vivitar 285 produces a nice catch-light in the eyes.
...Using the 75 or 90 degree angle directs the light almost directly over your subject's head which will probably cause the eyes to be in the shadow of the head.
...To compute exposure manually, measure or estimate the distance from flash to reflecting surface, plus the additional distance to the subject. Divide your guide number by this distance and open your lens one stop.
...Another method in an average size room is to determine the flash to subject distance. Then open your lens two stops.
Automatic Flash:
...Your flash may have two or four automatic exposure controls.
...This exposure is controlled by a thyristor circuit.
.......a. Purple color = 2 to 11 feet.
.......b. Blue color = 2 to 15 feet.
.......c. Red color = 5 to 30 feet
.......d. Yellow color = 6 to 60 feet.
...Changing to a faster or slower film speed will not change these distances -- only the aperture.
...Shooting at a distance less than these numbers requires less light and the thyristor circuit will cut off the light, saving some electricity for the next picture.
...Test the exposure using the sufficient light indicator (if available).
H. Automatic exposure with bounce flash:
...Set your flash on a color setting. Using open flash button, watch for a flash of light through the green button.
...If green light fails to light, move closer to subject or try another color setting. Your unit may not have the same color settings as mine.
I. Multiple flash:
...Using two strobes of equal power, place the main light in a front 45 degree position 8 feet from the subject.
...Placing the fill light (on camera) 8 feet from the subject produces a 2:1 lighting ratio.
...Moving the camera light back to 11 feet produces a 3:1 ratio.
...Moving the camera light back to 16 feet produces a 5:1 light ratio
...Note how f stop distances can control light ratios. Each distance is increased approximately 50% or 1 stop worth of distance to change the ratio.
J. Synchro-sun or flash fill:
...The aperture controls the flash exposure--your shutter speed controls the daylight exposure.
...Remember you can use slower shutter speeds for more sun-light exposure if blur is acceptable.
...Do not use faster shutter speeds than your manual recommends for flash. If you do only a part of the film will be exposed.
K. Artistic Creativity
...Your artistic creativity will determine if you use front 45 degree, side, or back lighting from the sun.
...The flash exposure can be controlled by either the aperture, flash distance or power ratio, if available on your flash.
...If the sunlight exposure (for example) is 1/125 at f11 and your guide number is 110, the flash at ten feet will produce a 2:1 ratio.
........a. This could result in slight over-exposure due to the overlapping exposures on the sunny side. Try closing lens one stop.
........b. Moving flash back 50% father to 15 feet will produce a ratio of 3:1
........c. Moving your flash back another 50% or 21 feet produces a 5:1 ratio.
........d. To shoot closer than 10 feet, you can close your lens down 1 stop (f 16 ) at 1/60 and shoot from 7 feet for a 2:1 ratio.
........e. If you want to shoot flowers at 5 feet, change the exposure to f 22 at 1/30 at 1/30 second.
........f. Some of us have flash units where the light output has a power ratio:
............1/125.....F11.....Full..........10 feet.
............1/125.....F11.....1/2..............7 feet
............1/125.....F11.....1/4..............5 feet
............1/125.....F11.....1/16........ 1/2 feet
........g. We can also control shooting distance by changing shutter speed, aperture and flash ratio.
...............................................2:1...............3:1.............5:1 ,
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...1/125.........F11................10 feet...........7 feet.........5 feet
...1/60...........F11..................7 feet...........5 feet...3 1/2 feet
...1/30...........F11..................5 feet.....3 1/2 feet...2 1/2 feet
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