 Scott Markowitz |
Flash Lighting Question I have a beginner's question on flash sync speed... My digital camera: Sony DSC-F828. When I shot a flash photo at f8, with shutter speeds of 1/30, 1/60, 1/125, 1/250, 1/500 and 1/1000, all areas of t5he scene being lit by my flash shots appeared to have the same exposure. I assume this is because my camera's flash hotshoe was synced to each shutter speed I selected. The areas of the scene lit with a continuous tungsten bulb appeared to grow dimmer with faster shutter speeds (at 1/1000 it appeared the tungsten bulb was hardly emitting a glow at all, and the bulb could clearly be seen in the shot). Therefore, if I changed the f-stop to, for example, f4, I could not use shutter speed to compensate for the larger aperture (in an attempt to keep the same exposure). So if I wanted less depth of field to throw the background out of focus by opening up to f4, the only way to match the original exposure would be to back off the lights to a meter reading of f4. At 1/30 it looked as though the ambient tungsten light (I included the lamp and bulb in the frame) had equal influence over the entire scene with the flash light, while at faster shutter So the only effect shutter speed has when using the hotshoe or a sync cable to fire a flash is to affect areas of the scene not being reached by the synced flash light, or to stop the action to more or less of a degree. However, the areas of the scene lit by the flash (with regard to exposure) are apparently not affected when changing shutter speeds. Is all that correct? Thanks,
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Flash is more a function of aperture because the flash light last only a small part of the time the shutter is open. Ambient light is more a function of shutter speed because it affects the negative for the duration the shutter is open. Shutter speed will affect the use of flash when the shutter speed is slow enough to allow ambient light to give extra exposure on top of the flash exposure. Your high shutter speed pictures came out with subject exposed correctly with the dark background. This due to the brightness of the flash light falling off as it got farther behind your subject, making it too weak for the chosen aperture. And also the shutter speed was too high for enough ambient light to add anything significant to the exposure. As you dropped the speed down, you allowed more ambient light to add to the exposure, making the background lighter. When you got to 1/30, that was the point where ambient light had enough time to blend in with the flash light. Keep getting slower and the ambient light would have piled on top of the flash light, making it look too bright. And most likely causing a ghost image of the exposure from flash, with a blurred image from ambient light.
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Scott Markowitz |
Hi Gregory. Thanks for your reply. That's what I thought about the ambient light. What about flash sync? Isn't the flash on for the duration of the shutter being open if the camera is sync'ed to the flash? That's what I understood it to mean, and why I think the exposure on the flash-lit subjects in the foreground always looked the same (never darker or lighter from 1/60 through 1/1000). Thanks,
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
No it's not. Flash typically fires at the very beginning. Flash is syncronized to go off at a certain time when the shutter opens, and using one that's too fast will have the flash going off as the shutter begins to close. I was surprised that a sony could sync at 1000. But if like on many slr's, a sync somewhere around 125, if you went above it, you'd have part of the frame dark all the way across because the flash fired when the shutter was closing.
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Jon Close |
The Sony can sync at all shutter speeds because it does not use a focal plane shutter, or even an in-lens leaf shutter. There is no physical shutter at all with this type of digital camera. The digital sensor is always exposed, feeding an image to the electronic viewfinder and/or the LCD. The "shutter" is just an electronic circuit that times the recording of the image.
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Scott Markowitz |
Thanks Jon for your reply. So was I correct in assuming with this camera that the flash would be lit for the duration of the electronic shutter circuit being "open"? Even so, I'm not sure I understand why the flash-lit objects in the image always appear the same with all shutter speeds. I would think the longer the shutter speed, the more flash light I'm letting in through the lens, and the lighter (more overexposed & washed out) the objects should be. - Scott
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Because the it's not lit by the flash for the duration of the shutter speed. The flash only last for a fraction of the 1/1000 that the shutter is open. And it's the same quick burst if the shutter were 1/250. It gets overexposed when you have a slow shutter speed that has light coming in, in addition to the intial quick burst of light from the flash. Extreme example. A room with no light. Take a picture with the flash and the shutter speed is 10 seconds. The flash pops at the beginning of the exposure and for the rest of the exposure, the shutter stays open. Use 1/500 shutter speed, the same thing happens, just the shutter stays open for shorter time.
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Scott Markowitz |
Thanks Gregory. That really clears it up, and confirms what Jon stated. Appreciate the help guys! -Scott
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