pre-flash
Many digicams employ a slightly different system for TTL exposure. First they fire a pre-flash, which is measured, and they calculate exposure based on that. This happens so quickly that the eye notices only one flash.
PPI ...
Pre-Flash - Some digicams use a low-power flash before the main flash to set the exposure and white balance. This does not allow the use of a normal photo slave strobe as it will be triggered by the pre-flash.
Pre-Flash. Some digicams use a low power flash before the main flash to automatically set the exposure and white balance.
Programmed AE. The camera chooses the best shutter speed and aperture automatically.
Monitor Pre-flash(es)
When performing Automatic Balanced Fill-Flash with TTL Multi Sensor, the Speedlight fires a series of scarcely visible pre-flashes to enable the camera's computer to pre-analyze the scene.
Pre-flash triggers my studio strobes!
TechTock reader Anthony Dayton asked us for tips on overcoming the problem of his DSLR's built-in flash's evaluative pre-flash for triggering studio strobes while staying wireless. We've got some quic Read more ...
pre-flash std. maxtrix metering taken PRIOR of the actual exposure
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TTL flash metering
DURING
exposure ...
Pre-flash TTL metering (flash fires twice)
External flash
Yes, Sony synch terminal and "dummy hot-shoe" (no connectors) ...
It can be prevented by adjusting the camera angle, being sure the subject does not look straight at the flash, or with a redeye-reducing pre-flash.
In this mode the flash tube emits a pre-flash and the camera's evaluative metering system is used to determine flash exposure.
The first one is a pre-flash, half a second before the real one. The point of the pre-flash is to trigger the pupils to shrink, reducing the chance for red-eye. Unfortunately, it doesn't eliminate red-eye, it just tries to lessen it.
The solution is to turn off the camera’s red-eye reduction and hence eliminate the pre-flash. Some of the better digital point-and-shoots have a special slave mode and both of the models I use feature this.
This works with a pre-flash prior to the flash used for exposure and does reduce the red-eye effect often seen when photographing people indoors. Flash off, or flash defeat turns the flash off even if the light is low.
3D Multi-Sensor Balanced Fill-flash An automatic, balanced fill-flash system in which the flash fires a series of pre-flashes just before the first shutter curtain moves.
The most common method in use at the moment is the 'pre-flash', which is usually a series of flashes fired quickly just before the shot to try to close the pupils of your subject(s) and thereby lessen the problem.
Alcohol dilates pupils so even the pre-flash flash won't help - your subject may simply be too sozzled to allow you to get a shot without red-eye. Don't fear, even this scenario is fixable by simply 'burning' the red eye in Photoshop.
Happy flashing! ...
Red eye reduction fires a pre-flash to prevent large red eye pupils appearing. 'Off' turns an automatic flash off so that the camera can be used with a long shutter speed for night photography.
Some digital cameras need special slave strobes because they fire a pre-flash before the actual flash for the picture. This pre-flash fools the slave strobe causing it to fire before the picture is taken. (See Flash Sync) ...
A method of reducing or eliminating red-eye from flash photographs by using a short burst of light, or pre-flash, to momentarily ‘stop-down’ the pupils of the subject’s eyes prior to the actual flash exposure.
When using two flashes make certain the triggering flash is not making pre-flashes. To avoid them, simply tilt or rotate its head a little. When "straight forward" is used here with two flashes, it should be understood as "almost straight forward".
There is a delay between the pre-flash which reduces red-eye and the actual exposure. As a result often you miss the shot, especially when photographing children. If you turn this feature off you can fix red-eye on the computer later.
Feature found in most cameras which reduces red-eye by firing a series of weak pre-flashes before the final flash exposure is made.
Aperture
The variable opening inside the lens, which regulates the intensity of light striking the image sensor.
This first light is known as the pre-flash. It then measures the amount of light returned through the lens and compares it with the original amount of light emitted, taking into account the distance between the camera and the photographed subject.
Cinematographers do not "white balance" in the same way as video camera operators; they can use techniques such as filters, choice of film stock, pre-flashing, and after shooting, color grading (both by exposure at the labs and also digitally).
TTL is a slight modification of Through The Lens metering where the digital camera and the strobe communicate via a series of pre-flashes, microseconds before the shot is taken.
(Evaluative-Through The Lens) An exposure system that uses a brief pre-flash before the main flash to calculate the exposure index (used by Canon®).
EXIF ...
E-TTL (Evalulative-Through-The-Lens Metering) is a flash metering systems designed by Canon, in which the flash unit fires a pre-flash burst prior to the main flash firing in order to get a more accurate metering reading for a more correct exposure.
E-TTL
E-TTL (Evaluative-Through The Lens) flash metering. A Canon EOS flash exposure system that uses a brief pre-flash before the main flash in order to obtain a more correct exposure.
(see Balanced Fill Flash & EOS) ...
(10) Battery life is extended when using strobes like Inon that "quench" the internal flash of the E900 by emitiing a pre-flash
(11) The S&S wide angle lens increased field of view to 85 degrees underwater
Micro four thirds cameras ...
A pre-flash makes the eye's pupil contract and lessens the red-eye effect. It is not very effective though.
Red-eye reduction mode fires a pre-flash that is supposed contract the pupils of your subject's eyes thereby reducing the flash reflection in their eyes from actual flash exposure that immediately follows.
Turn on lots of lights to make your subject's retinas smaller, this will allow less light to bounce off them.
Use "red eye" reduction mode on your camera, this sends a "pre-flash," or "red eye reduction" flash, ...
To eliminate red-eye, many cameras have a "red-eye reduction" mode. This mode works by firing a short pre-flash lamp or a burst of flashes to close the subject's iris a moment before the actual flash fires to take the picture.
The effect will appear more often, if the the pupil is opened wide and the closer the built-in flash is near the axe of the objective. As a counteract, they will try to reduce the red-eye-efect by using a bundled ambient light or pre-flash for the ...
the ambient light, increasing the angle between the lens and the flash beam with a bracket, having the subject look into a direction other than the camera, or into a bright light, or simply by using a flash with a red-eye system which pre-flashes to ...
 See also: Camera, Light, Image, Flash, Exposure
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