D300 built-in flash, Part 1: Blinding speed

Started Dec 25, 2008 | Discussions thread
David314 Veteran Member • Posts: 4,790
Re: Flash, PC sync and shutter timing

Marianne Oelund wrote:

The PC sync signal start edge is located at exactly the same point in
the shutter cycle as the trigger pulse for the built-in flash, within
about 1us. The PC sync ends 7.1ms later. However, the PC sync pulse
is only issued when the built-in flash is off; you can only have one
or the other.


the reason i ask is you can see the start and stop of the trigger pulse using the sync signal very clearly

I put together a setup this weekend, which provides inputs for the
scope, corresponding to light shining on the sensor's bottom and top
edges. This is an alternative way of measuring the shutter/flash
timing, and is somewhat more direct. (The only difficulty is
aligning the optical sensors to accurate edge positions, which took
me a couple of hours of tweaking!)

yeah, only a couple of hours?

and please take the following as honest feedback and inquiry

your cursor A position is showing the top of the sensor uncovering 200usec before the flash is firing - that seems like a lot of time

so again to me - as practiced skeptic I would look for confirmation of this

and that confirmation would be seeing the shutter open and the flash not going off - and on the other end, the flash going off and the shutter partially closed (although as you previously pointed out there is other evidence of this)

so - if i could see a picture of the shutter, the flash, and maybe an LED being driven by the sync signal all in the same frame - that would show quite graphically what is going on and would remove any issue with sensing the edge and tweaking the photo transistor window position

i suppose i should walk the talk on this one but since my second camera is a D40, not sure it is up to the task

thanks for the amazing work


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