The discussion revolves around the phenomenon of pre-flash in digital cameras, exploring its purpose, effects on subjects, and the technical aspects of flash photography. Participants examine the implications of pre-flash on red-eye reduction, exposure settings, and the physiological responses of subjects being photographed.
Participants express a range of views on the purpose and effects of pre-flash, with no clear consensus on its implications or technical details. Some agree on its role in reducing red-eye, while others question the relationship between flash and digital cameras.
There are unresolved questions regarding the exact mechanisms of red-eye reflection and the technical specifications of flash systems in modern cameras. Participants also note the dependence on camera design and user settings.
pivoxa15 said:When taking photos with a digital camera there is usually a burst of light before the photon is taken. Why is this? Is it because there is usually not enough light reflecting off the object being photographed. It is this reflected light that is what is being recorded on the film inside.
Give khalil a prize. The reason that pre-flash is prevalent on digital cameras is that most of them are very small all-in-one units, meaning that the flash is very close to the lens so the light bounces straight back from the subjects' eyes, giving a really bad case of red-eye. Most of these are designed for snapshots (point and shoot) and are not aimed at the part of the market that would understand or use bounce flash even if it were available. Also, bounce flash can be very hard on battery life - not a good thing in a pocket-sized camera that uses AA batteries and has to use battery power for auto-focus, exposure control, image capture, etc. If you double the path-length of the light from the flash, you have to quadruple the intensity of the flash to achieve the same level of illumination assuming you are bouncing of a perfectly reflective surface.khalil said:However what i think you really mean is the "red eye effect", the retina of the human eye reflects red light straight back in the direction it came from, pictures taken from straight in front of a face often exhibit this effect. It can be somewhat reduced by using the "red eye reduction" found on many cameras (a pre-flash that makes the subject's irises contract). However, really good results can be obtained only with a flash unit that is separated from the camera, sufficiently far from the optical axis, or by using bounce flash, where the flash head is angled to bounce light of a wall, ceiling or reflector.
khalil said:a physiologic pre-flash effect: my guess is a smile... or something of the sort if that is what you mean...
Anyways i do not see what is the relation between flashes and digital cameras. The idea is to illuminate better to better expose a photo or capture fastly moving objects in an "instantaneous" manner (1/1000 sec).Xenon gas is used mainly .
However what i think you really mean is the "red eye effect", the retina of the human eye reflects red light straight back in the direction it came from, pictures taken from straight in front of a face often exhibit this effect. It can be somewhat reduced by using the "red eye reduction" found on many cameras (a pre-flash that makes the subject's irises contract). However, really good results can be obtained only with a flash unit that is separated from the camera, sufficiently far from the optical axis, or by using bounce flash, where the flash head is angled to bounce light of a wall, ceiling or reflector.
turbo-1 said:Give khalil a prize. The reason that pre-flash is prevalent on digital cameras is that most of them are very small all-in-one units, meaning that the flash is very close to the lens so the light bounces straight back from the subjects' eyes, giving a really bad case of red-eye. Most of these are designed for snapshots (point and shoot) and are not aimed at the part of the market that would understand or use bounce flash even if it were available. Also, bounce flash can be very hard on battery life - not a good thing in a pocket-sized camera that uses AA batteries and has to use battery power for auto-focus, exposure control, image capture, etc. If you double the path-length of the light from the flash, you have to quadruple the intensity of the flash to achieve the same level of illumination assuming you are bouncing of a perfectly reflective surface.
That's it, essentially. The retina has more blood vessels per unit are than any other part of your body, and so it looks very red when illuminated.pivoxa15 said:flash and pre-flash? So there are usually two flashes when a photo is taken, one very quickly in succession of the other.
So all cameras must have a flash to illuminate the object being photographed but the retina reflects red light only so the flash causes red eyeness. Therefore a pre-flash is equiped to get rid of this feature by narrowing the iris where light can get through.
Yes. I'm not sure if the strategy is to keep the pre-flash intensity at a lower level or perhaps to keep their duration very short.pivoxa15 said:With modern cameras is the pre flash and flash done with the same light globe?
jtbell said:When my camera is set to red-eye reduction mode, I actually get three flashes! I think the first one is used to help the camera set the exposure automatically (by measuring the reflected light from the scene), the second one narrows the subject's eye pupils to reduce the red-eye, and third one illuminates the scene when the shutter opens.