Hans wrote in connection with the F280 ,FP mode
<< In FP Mode, the GN is shutter speed
dependent, from 14m at 1/60 sec to 2.6m at 1/2000. The 5400HS is twice at
powerful. It needs to be, of course, to be of any use at 1/8000 sec. >>
Hnz,
What GN's do they quote for the FP mode for the 5400HS and what is the angle
of coverage of the flash? If they use a vertical shutter on the camera I
would
actually expect the GN to be greater than twice the OM for the FP mode.
The shutter travel time for the same shutter travel speed would be only 66%
of the OM time increasing available energy by about 60% and hence available
GN by approx the square root of 1.6. If they have a faster shutter travel
speed,
as is likely with a 1/8000 max speed, then again I would expect an even higher
FP GN. So the camera shutter design affects the FP mode very significantly
and the GN for FP mode on the Minolta might even be more favourable
for the Minolta.
Similarly if it has zoom head or has a maximum angle of coverage narrower
than the F280 (24mm lens) then again I would expect an even higher GN.
Unfortunately the FP mode is not really any serious competition for decreased
shutter travel time (or a leaf shutter) but is great for fill flash.
=======================
Start General Rant about GN's :
=======================
Many third part flashes only cover 35mm lens as standard thus greatly
increasing (inflating) their
GN's over the OM flashes which mostly cover 24mm. Obviously an advantage for
the
wonderbricks over OM are the automated zoom flash heads that auto adjust as
you zoom
rather than the manual zoom heads like the T32 add on or the third party zoom
head flashes
for OM.
Theoretically the area covered by a 24 mm coverage flash is about 1.77 times
a 35mm flash.
(angle of coverage squared).
Thus we would expect the GN to go down by a factor of about 0.56 if we widen
a 35mm flash to
cover 24mm. (This seems to agree approximately with practice based on
numbers below)
It is interesting to compare the T32 to say the popular old Vivitar 4600/5600
flashes
with standard head. (as commented recently GN's are greatly inflated by
vendors
so this is assuming GN's are true as stated by the vendor!) As a sanity check
I also
calculated the GN's assuming no light loss from adapters and using lens
coverage
angles from Hnz's SIF info.
at 100ASA: GN
T32 GN in ft 104 (24mm coverage) <==
4600 standard head 100 (35mm coverage)
4600 with WA adapter 70 (28mm coverage) (calculated value 70)
4600 calculated for 24mm 56 (no adapter available for 24mm) <==
4600 with extra wide adapt 50 (21mm coverage) (calculated value 47)
T32 with 21mm adapter 72 (21mm coverage) (calculated value 83)
The T32 has a smaller volume than the 4600 but has almost twice the
effective GN. Since the GN increases as approximately the square
root of energy stored (Joules or W-s) all things being equal ,
the T32 is really much more powerful than the
4600 although superficially they have "the same GN".
Interestingly Olympus's zoom head adapter for the T32 appears to be very
inefficient
as the GN does not increase as much as one would expect. (numbers not shown)
The manufacturers GN's for the 4600 with adapters look rather optimistic
given the adapters probably loose some additional light.
The 21mm WA adapter for the T32 has significant loss over theoretical.
Somebody with more time could check some of these numbers with a flash meter.
Here are some more comparisons based on GN's I could find for various flashes:
I own a Sunpak 544 potato masher with a 35mm coverage
GN of 140. this equates to a GN of about 79 for 24mm coverage, less than
that of the T32. The 544 has other features that the T32 does not, but it is
a
much larger flash.
The well known high power potato masher Metz 60ct-4 has a GN of 197 with
28mm coverage. This translates theoretically to about GN 157 at
24mm coverage but this is a huge heavy flash that costs $500+
GN 157 is not that much more than the 148 or so of the T45.
The Cannon Speedlite 480EG (a patato masher) has a GN of 160 at 28mm coverage.
This would be about GN 127 at 24mm.
The Nikon SB 14 potato masher has a GN of 105 at 28mm.
This would be about GN 84 at 24mm.
The Nikon SB26 has a good GN of 118 but I could not work out
at what coverage angle ....
Caveat Emptor: Flash vendors of zoom head flashes often specify the
GN at the 50mm setting when generating sales literature so you
need to read the detailed specs when doing comparisons of GN's.
So the T series flashes achieve quite high GN's for their coverage angle
especially given their compact size.
I like the wide angle coverage as standard.
Somebody better sanity check my calculations but they seem to
agree reasonably with the 4600 Vivitar data.
END Rant
=========
Tim Hughes
Hi100@xxxxxxx
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