D300 built-in flash, Part 1: Blinding speed

Started Dec 25, 2008 | Discussions thread
OP Marianne Oelund Veteran Member • Posts: 7,255
Look closer

David314 wrote:

SB800 triggered by D300 1/64 power D40 at F10 1 sec exposure taking

no sign of the shutter

You caught it.

Look carefully at the upper edge of the sensor, and compare to frame 3 of my latest sequence (which is only about 30us earlier than your photo). See the gray edge hanging over the very top of the sensor? Compare to frame 4 of my sequence to see how it differs when the shutter curtain is completely retracted.

without the flash in the sequence pictures you can't relate the
shutter position in the pictures back to the scope traces

All of the information you need is there, because the time values included with the photos tell you the exact moment of the photo, relative to the flash trigger (which is the same time as the PC sync start edge).

Referring to the sequence shown in my Part 2 post, the key frame is frame 8, which is at -0.20ms (-200us) before the flash trigger, and shows that the front curtain is almost exactly at the top row of pixels on the sensor. [If you cut/paste frame 8 and place it next to frame 9, you can see how closely the curtain position matches the top pixel row position.] Thus it tells you that the last row of pixels is uncovered almost exactly 200us before the flash is triggered, in agreement with yesterday's composite sequence and scope traces with the phototransistor signals.

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