Friday, October 01, 2010

Friday: "Flash Power Demystified"

Good Afternoon Everybody,

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I can't believe it's Friday already. We are going to try to take off a bit early today so let's get right to today's post.

"Flash Power Demystified"

I received lots of emails and even questions during our "Captured By The Light 2010" tour [link] about flash power. People will ask if they can do the same kind of lighting with their Nikon SB800, SB900, or Canon 580 strobes as I do with my Quantum T5d-r strobe.

Well, the answer is of course, yes. Remember, it's just light and light  - is light  - is light. The difference in the strobes mentioned is the rated power output of each one. I think this is where some of the confusion occurs. So today, let me give you the low down on the output power of each strobe and then we will take the discussion further.

Hit the “Read More…” link below for the rest of the story.

Flash Power Output Per Model

DAZNOTE: Without going into a lot of confusing explanations of what a watt-second is, let's just say it's a measurement of the strobes power or light output. The bigger the number, the more light per flash cycle.

Quantum Flash Quantum QFlash with Qpack-X  module: 200 watt seconds of Raw power upgradable all the way up to 2 heads totaling 800 watt-seconds – WOW!!

Quantum T5d-r with Turbo battery: 150 watt-seconds. This is my choice by the way.

Quantum Trio powered by Turbo battery: 80 watt-seconds of fire power as fast as you want to shoot without ever over heating.

Canon 580EXII Canon 580 EXII: About 50 watt-seconds. This is my normal on camera (fill) flash.

Nikon SB800: Also about 50 watt-seconds.

Nikon SB900: About 80 watt-seconds. Be careful, I've heard several reports that shooting these puppies at "full tilt boogie" will cause them to overheat and shut down till they cool off.

How I Shoot, How You May Shoot

Now let the discussion begin. I shoot the Quantum T5d-r attached to one of their turbo batteries. As I said, that gives me about 150 watt-seconds of fire power which is pretty sweet when I need lots of power for off camera flash outdoor shooting.

Wind Dancers - Final DAZNOTE: Remember, when shooting outdoors I'm limited to the flash sync speed on my camera, about 1/250 second. That means I need to use smaller apertures when shooting outdoors. And smaller apertures mean I need more flash power to make the exposure.

Sure, you can get by with the shoe mount flashes, but you would need three of them to equal the flash output of my Quantum. At that point, you are near the cost of the Quantum and have to deal with 3 strobes instead of one. That just complicates issues too much for me, hence my single strobe.

Umbrella just right On the other hand, most of my wedding day shooting is NOT at full power, but usually hovers around 1/4 or 1/8 power when shooting through my Zumbrella. That puts you within striking distance of the power output of the shoe mount strobes.

So could you use your show mount strobe to shoot through an umbrella?  Of course. Just be sure to pull out the wide angle diffuser so you get the maximum light spread out of the strobe to get full use out of the Zumbrella.

OK, remember too, if you are firing your shoe mount strobe at it's full 50 watt-second output, you will drain the batteries pretty quickly. The easy work around, goose your ISO to a higher setting. I personally would have no problem shooting at ISO 800-1600. That would give me plenty of lower power flashes to complete the shoot.

So, when you read at DPT that I shoot my Quantum at 1/4 power, that means I'm dumping about 40 watt-seconds of power per flash. If you want to duplicate the shot with your shoe mount flash, just shoot it at near full power for the same result.

If you read that I shot the image at 1/2 power or about 80 watt-seconds, know that you could use the Quantum Trio or Nikon SB900 flash and obtain the same result. To get the same result with your SB800 or 580EXII flash, just open up a stop or double your ISO.

DAZNOTE: This is important to note. I shoot my off camera flash on manual ALL THE TIME! I suggest you do the same even if you are shooting shoe mount strobes. It just gives you tighter control over the finished result.

Light LR - Fotolia_2176393_Subscription_MAnd always remember, light - is light - is light.

I didn't want today's post to turn into some super long dissertation on flash photography. I know the discussion could go on forever. I mainly wanted to draw some comparisons to the strobe I use and I thought you might want to compare light output-wise to the strobes you may be using.

Now when you see my power settings listed you can easily translate that into what you need to do with your strobes if your are using different strobes than my chosen favorite. Hope it helps.

Related article links:

Quantum Strobes [link]

Canon Strobes [link]

Nikon strobes [link]


Hey gang, That's it for me today. We've got bags to pack and vans to load. It's off to Nashville for the next leg of my CBTL2010 tour. I hope to lots of you next week in Music City.

Have a good one and I'll see ya' on Monday.



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  1. Hi suggest shooting off-camera flash in Manual flash mode all the time. This certainly makes sense for more static scenes like the formals. But how do you deal with changing flash-to-subject distances and other exposure variables in more dynamic scenes like dancing on the dance floor with the flash in manual mode? Is it that you rely on your assistant to always maintain a fixed flash to the subject distance? If so, how would you do it without an assistant?

  2. see ya monday! can't wait to help you out too!

  3. David, I love you like a brother but your estimates for the SB-800, SB-900 and Canon 580 EX II are just way off. :)

    Did you sincerely take all 3 of these flashes, set them to the same zoom settings, pop off several full flashes and see what the calibrated Sekonic light meter told you?

    This is exactly what I did. The 3 flashes above read 100% exactly the same meter readings under the same settings (50mm zoom, identical distance and full power output).

    Granted, if I set the zoom head of the SB-900 to 200mm, the meter read higher than the others, but thats not a higher W/s rating, thats just a greater zoom.

    Instead of believing some of the marketing BS manufacturers write, I invite you to do the same basic test I did... it is rather eye opening. :)

  4. A correction on your rating claim. The Canon 580EX is not 50ws. It actually is 75ws (76 actually). It has a 1400uF capacitor and at a 330v charge voltage this comes out to 76ws.

  5. David,
    Your on-camera flash of choice is a Canon 580EX for fill flash.
    Is there a reason why you don't use a Qflash Trio instead? You would have to carry a Qflash SC battery but you would get remote power adjustment of your remote T5DR.

  6. Love your book and videos. I appreciate the input from fellow viewers also. When I see your Quantum flash, I see it as a hard light source with lots of wasted - spilled light. Perhaps a barn door could better direct the light in this shot of rim lighting. Surely it would stop the lighting of the moon, stars and other things. Just an interesting comment. It would also make the 75 W/s output of the canon to be more utilized. Also I love the canon remote control flashes and the side port for a 6 or 8 battery pack which I have two six units. Upping the ISO on the 5D M2, barn doors, battery packs just make it possible for us to use the Canon (which I have 2) verse the great quantum flash and remotes.

    Have you ever used filters like the CP or ND to help with bluing your skies and allowing your shutter speed to drop back to 200 or so? I am interested in that question. Thanks