Pete wrote:
> There seems to be some confusion regarding flash duration. It's
> generally measured 2 ways. First is at t.05, or when a flash goes
> from 0.5 max brightness to max brightness, then back down to 0.5 max
> brightness ( all at a given watt sec rating ). This is the method
> used by most flash manufacturers, but isn't the best method, as
> exposure on film is still taking place outside these parameters. It
> also tends to overstate the ability of a particular flash to freeze
> action. The second, more accurate method is a reading at t0.1, or
> when the flash goes from 0.1 max brightness to max brightness, and
> backdown to 0.1 max brightness. This measuring method more accurately
> simulates the freezing effects of an equivalent shutter speed, as
> virtually no exposure will affect the film outside these parameters.
Thanks for this clarification.
> I'll check my SB-26 with my Broncolor flash duration meter tomorrow
> to find out what it's full power duration is at t.0.1.
Very interesting. I await your results.
Some days ago, I misinterpreted some data I gathered from the SB-28 manual
because I wasn't aware of how the High speed synchro works.
Now, what remains mysterious to me is why does the SB-28 guide number drop
from 42 at 1/60s to only 20 at 1/250s (I picked them from the SB-28 user's
guide)?
If the slowest flash fire only lasts 1/830s, why couldn't the flash give
the same light power?
I must miss something...
Thierry
