How to determine monolight Watt Second size

<p>Hey everyone,<br>

To level set, I shoot for a local adult sports league in my free evenings; I do not take this TOO seriously.<br>

Some of the stuff I shoot is in a pretty crappy lit gym. I want to buy two monolights (plenty of A/C plugs available) to bounce off the walls/ceiling for volleyball and basketball, but am not sure how many watt seconds I need.<br>

The gym is a typical basketball court, but is roughly 30 feet to the ceiling, with a track around the perimeter about 15 - 18 feet up. I was thinking of setting the flashes on the track, but will play with this when I get them.<br>

I am looking at some 600 WS flashes on Amazon that come with battery packs because I love outdoor shooting, and figured I could re-purpose them. I'm not TOO concerned about color stability... as of right now I am shooting in a poorly lit gym at 4000 ISO @ f/2.8, so I always have to adjust my WB in Lightroom.</p>

<p>During the day I am a statistician, so my personality makes me want to have a way of knowing how these different WS lights will act - but can not find anything. Can anyone help me, please?</p>

To make it easy: (the following base numbers are made up but the formula is true.)

If 100 w/s produces enough light so you get f/2.8 @ISO 100 at 20feet:

 

200 w/s will get you f/4

 

400 w/s will get you f/5.6

 

800 w/s will get you f/8

 

1600 w/s will get you f/11

 

...

 

This is if all things are equal. However there are differences in electronics and more importantly reflector design between

brands.

<p>The only way to figure it out is to test them (I'd use a flash meter). Make sure you can return the strobes if they don't work out. <br>

Also, what re-cycle times do you need?</p>

<p>I'd call Paul C. Buff and talk to their techs and see what they say.</p>

<p>Thank you! </p>

<p>You want to bounce off the ceiling 30 feet high. So the light goes up and down, making a 60 feet round trip.<br /> Ceiling reflectivity, even if it is white, you will have additional abrosbtion/reflexion loss of light.</p>

<p>Perhaps bouncing off a distant wall will have even longer distance travel.</p>

<p>2 of 600 WS would be minimal power to consider, and use high ISO and fast lens.</p>

<p>I would recommend stronger flashes, like 2400 WS or 1800 WS. 4 of them, strategically placed would give more comfort.</p>

<p>However, since you are: "<em>I do not take this TOO seriously</em>" - anything would do. Just verify results instantly and make any adjustments needed.</p>

<p> </p>

Empirical knowledge is always best. Consider renting the most powerful but portable set up you can find (I suggest

http://www.lensrentals.com or www.calumetphoto.com) and see how far down you can dial it and still get acceptable

results at the highest ISO you are comfortable with.

<p>See if you can find a copy of the Jon Falk book "Adventures in Location Lighting." It's from 1990 and about 95 percent out of date, but he has a good section on rigging studio strobes for a basketball arena for Sports Illustrated. I think everything he used was either 1200WS or 2400WS and he might have mounted a dozen or more units up in the rafters. Of course this was for shooting on slow-speed slide film so you could probably scale things down considerably from what he had to do. But the strobes would definitely be used direct, not bounced. Why waste all that light?<br /><br />A little more down to earth is <a href="http://www.strobist.com">www.strobist.com</a>. David Hobby has a section there on lighting a high school gym with speedlights. That's probably much more in line with what you need to do regardless of what kind of flash unit you use.<br /><br />Before you do anything at all, talk to the league/coaches and make sure they don't have a problem with flash during their games.</p>

<p>That is a difficult problem, best solved by metering the actual situation in advance.</p>

<p>But you said bounce on 30 foot ceilings. </p>

<p>Assumptions: Calling it 25 feet from head-height up, that's 50 feet round trip, up and down. But there is the trig of the longer diagonal distance, both up and out onto the court. Maybe a max case is 45 degrees, or 1.4x more, or 50x1.4 = 70 feet light path.<br>

<br />Paul Buff publishes Expected Output for his units, at<br>

http://www.paulcbuff.com/output.php</p>

<p>If you select the OPTIONAL 11 inch long throw reflector (50 degrees) for the chart, he computes Guide Number 394 (ISO 100) for 640 watt seconds. The 50 degree reflector should cover 167 feet at 70 feet.</p>

<p>ISO 400 would double the Guide Number, say GN 788.<br>

ISO 1600 would double it again.</p>

<p>GN 788 / 70 feet is f/11.2 (technically f.11.3 is what we call f/11). However, you will lose about another stop (50%) at the reflection surface, assuming it is a halfway white ceiling that can reflect 50%. </p>

<p>So near f/8 maybe, ISO 400. Sounds optimistic, but those are the numbers. Multiple lights put out added light of course.</p>

<p> </p>