Sunday, September 16, 2007

Norman P1250D: Watt-Sec to GN Calculations

I recently had a stroke of good fortune - a retired photographer living in my parents' subdivision in Florida was selling a Norman strobe kit for $500 and through them offered it to me. Thinking this would be a great way to earn of few easy dollars, I did a little auction tracking on eBay to determine if a resale would make any money - not really. I told him so and suggested that he sell it himself - getting $500 should be a cinch. Another week goes by and my Dad calls to ask if I'd take the kit for $300 plus $70 in shipping. Say what!? The rest is history...

I now own an awesome 4-head Norman strobe kit, which includes:
Norman P1250D watt-second power pack
(4) LH2000 2500 w-sec lampheads with 150W halogen modeling lights
(1) 8.5" high output reflector
(1) 5" high output reflector
(1) 5" rotating barndoor ass'y
(2) 16" soft light reflectors
(2) 16" rotating barndoor/diffuser assemblies
(1) R9110 Rapid Cool blower fan
(2) 42" shoot-through white umbrellas
(1) 42" Westcott Halo umbrella softbox
(1) metal Norman snoot
(1) 42" collapsible fabric gobo
(2) heavy duty steel light stands

"So what's a 1250 watt-second power pack gonna make for light?", I ask myself as I clean and set up the new gear. Watt seconds is a "fools errand" as they say on Pirates of the Carribean - it doesn't apply itself readily to flash photography. No iTTL or automation - just lots of metering to create main/fill/key ratios based on personal experience.

Besides, strobe photogs are more interested in the apertures they can shoot at - DOF and bokeh are what really matter - and creating beautiful light, of course. So to make the GN conversions for a flash power reference, I put the following lighting reflectors, diffusers and umbrellas through a "watt-seconds @ 10-foot X ?? aperture" benchmark test to determine the range of GN's produced with the various power setting/modifier configurations.

250 watt-seconds @ 10 feet
8.5" high output reflector: f13 = GN 130
16" soft surface reflector: f13 = GN 130
16" soft surface reflector w/ diffuser: f9 = GN 90
Halo 42" umbrella softbox: 7.1 = GN 71
24" silver umbrella: f5.6 = GN 56
24" 'deep' silver umbrella: f5.6 = GN 56

750 watt-seconds @ 10 feet
8.5" high output reflector: f22 = GN 220
16" soft surface reflector: f20 = GN 200
16"soft surface reflector w/ diffuser: f16 = GN 160
Halo 42" umbrella softbox: 14 = GN 140
24" silver umbrella: f11 = GN 110
24" 'deep' silver umbrella: f9 = GN 90

1250 watt-seconds @ 10 feet
8.5" high output reflector: f29 = GN 290
Halo 42" umbrella softbox: 18 = GN 180

The Norman P1250D power pack has a maximum of 1250 watt-seconds (really?) with switchable 250, 500 and 750 watt-second settings. Each LH2000 lamp head uses a 150-watt halogen modeling light which can be set to correspond to the lighting ratio between lamp heads for a consistent preview. At the power pack, I can plug in as many as four lamp heads in the following combinations: 1@1250, 2@750/500, 3@750/250/250, 3@500/500/250, 4@500/250/250/250 or 4@250/250/250/250.

Got the owners instructions from Holly Enterprises in North Hills, CA - many thanks Brent for your help! I have a much better appreciation for the Norman brand now...

Needless to say, this just scratches the surface, but I am loving every minute of this gear and have a whole new skill to learn!

Mule

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