I am casting around for a new flash gun. The choices to date seem to be
an Oly F280 or a Vivitar 285. The F280 has a guide number of only 91
[feet] at 100 ISO whereas the Vivitar 285 has a guide number of 120
[feet] at 100 ISO.
I tested a new-out-of-the-box Vivitar 285 today with a flash meter at 10
feet at 100 ISO and found the output to be only f 5.6! At 5 feet the
reading was f 8 ..... in both instances two full stops of underexposure
or, in other words, only 250f rated output.
I am wondering whether my experience with the flash meter with the 285
was to be expected or whether list members who use, or have used, the
285 can vouch for a better level of performance. Clearly, the loss of
750f output does not speak very highly of what should be a respectable
flash gun.
As far as the F280 is concerned has anyone got any test statistics with
a flash meter to compare actual output with rated output? Any
significant fall off in actual output at GN 91 at 100 ISO would start to
produce underexposed images at relatively close range indeed. Using the
F280 for fill flash at short range might produce satisfactory results
but a fall off in actual versus rated output at full power would produce
seriously underexposed images at the rated distance for any specified f
stop.
John Hudson
Vancouver, BC
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