Macro the 1/f rule and flash duration

Started Sep 8, 2008 | Discussions thread
John K Veteran Member • Posts: 7,614
Re: Ooops, I should have posted one important point.

JimH wrote:

The time period shown in the upper right corner of the oscilloscope
is expressed as time / division.

And the screen divisions are very hard to see. There are ten
divisions across the screen. So the actual times are ten times what
you were lead to believe.

In shot 1, for example, the time is 20uS/division. So the actual
duration of that flash pulse is more like 40uS (1/25,000th).

Sometime, I'd like to get a good digital oscilloscope. In this case,
I was using a good-old analog storage scope which makes things a bit
harder to read, particularly when looking at photos of its screen and
not seeing it "in the flesh".

I think in my original thread about this, I did mention all of that.
But I failed to say it this time.

Sorry for the confusion, it's my fault for just posting the photos
without the proper annotations!

There seems to be some confusion Jim when people see your results in that they think the whole "motion blur with flash problem" is over rated because your pulse widths are so short. But the problem is that you'll never get those short duration pulses when shooting a photo in the real world -you need a lot more light than a 1/25,000 of a second pulse can provide. I wish there was a way to measure the pulse width when shooting a standard gray card at different magnifications -still not an accurate test of real world conditions but it would be a little better than just testing each power level.

Since most commercial diffusers block at least one full stop I've switched to using some engineering samples that a company sent to me (sorry, can't name them) and the plastic that I'm currently testing only blocks 2% of the light passing through it (a full stop would be 50% light transmittal). So far the level of detail that I'm getting has been excellent...

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