This is exactly what I was looking for, a sensible, well written articel to help me understand my flash.

Chris

If you have the kindness please tell me if i can use an external flash unit such as 580ex ii to make some Chiaroscuro shoots in black&white.

I know you to do that using additional lights but is there any technique to produce Chiaroscuro via an external flash unit ???

Warm Regards and thanks again for your great article

Most DSLRs have two curtains for the shutter. When you release the shutter, the curtain covering the sensor pulls back to allow light to hit the sensor. At lower speeds, the second curtain closes across the sensor to end the exposure only after the first curtain is fully open. For however long the shutter speed is, there’s a slit between the two curtains of the full width of the sensor.

The curtains can do this sequential dance only so fast, however. For high shutter speeds, the second curtain starts to close before the first one is fully open. This allows very high effective shutter speeds, with the slit between the two curtains narrowing as the speed increases.

This causes a problem for the flash, though. The pulse of light emitted by the flash is of very short duration. At slow shutter speeds, this doesn’t matter, because the entire sensor is exposed to the flash while the first curtain is open and before the second curtain starts to move across. At higher speeds, though, there is no one moment at which the entire sensor is open for exposure – remember that the second curtain begins covering up the sensor before the first curtain has fully opened. Thus, when the flash fires, there will be a part of the sensor that is blocked off from the light and will appear black (or at least under exposed, depending on the exposure for ambient light).

High-speed flash gets around this by firing a series of flash pulses throughout the time that the curtains are moving. No matter when a given part of the sensor is uncovered by the curtains, flash will hit it. I don’t know for certain why high-speed sync is not enabled by default, but I imagine the reasons include: (1) that the effective flash intensity (“power” or duration, and range) must be lower in order to sustain multiple pulses and (2) that the flash may not be able to freeze high-speed action due to the longer effective duration of the pop. These would alter standard expectations and so one should have know that one wants them and choose to turn them on.

“I have no way to comprehend what some said about people not liking pre-flash…it is imperceptable. I would welcome more input via email from those who brought this subject to the table of discussion…thank you.”

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I tried to e-mail you on the contact page of your website as you asked but received a message from Yahoo! that noted that “this was not permitted from your URL.” I have no idea what that means so I thought I would communicate with you here.

Thanks for inviting me to e-mail you to continue the discussion. Following-up from your flash article regarding preflash blinks. As mentioned I do notice an issue with some very sensitive subjects blinking in the Delta T between preflash and recording flash. As I noted in the article comment this is not because of red-eye reduction. I do not use red-eye reduction.

The percentage is low but I would say one in 50 or so subjects will show some sensitivity to preflash. As noted I generally just go Manual in those situations and the problem is solved. I am not the only photographer that sees this problem. Several of my professional colleagues see this too. The issue is not related to a particular manufacturer.

I too can see the dark zone between preflash and recording flash when I fire my cameras but I am not sensitive to the blinking issue. The duration is real and it is there to see. I might pick it up as being more obvious because I know what to look for but some subjects seem to have a sub-conscious “protection” defense that causes them to blink in the duration.

Regards,

Bilka

I really enjoyed reading this. It’s not something that I am working with right now (point and shoot, my wife has a tight grip on the DSLR )

My wife leads the 4-H photography group locally and is soon to be doing a meeting on lighting and effects. I’m sure there is information here that could help.

Mike