Speedo 2405cx Operating Properly?

I recently purchased a used 2405cx pack with some 102 heads and after setting

everything up today I have some questions I'm hoping someone can answer for me

regarding power output. Before getting to my questions I should mention this is

my first pack - I've always used White Lightning mono lights where flash output

was a little easier to adjust (at least for this noob) so some of my 'issues'

may just be ignorance on my part.

I ran the following tests with a single 102 head with a Chimera softbox

connected to the first plug. I metered everything with a very reliable Sekonic

meter.

<br><br>

<table>

<caption><b>Speedotron 2405cx Tests</b></captio>

<tr>

<td>Isolate/Isolate</td>

<td>f/16 @ 125th of a second</td>

<td>400Ws</td>

</tr>

<tr>

<td>Combine/Isolate</td>

<td>f/22.3 @ 125th of a second</td>

<td>1200Ws</td>

</tr>

<tr>

<td>Combine/Combine</td>

<td>f/32.2 @ 125th of a second</td>

<td>2400Ws</td>

</tr>

</table>

<br><br>

Do the exposures look correct? Should tripling the power output (from test1 to

test2) only yield a one stop difference? How about the pack's max single head

output of 2400Ws. Does f/32 seem right here? Based on my experience using

300Ws white lightnings I was expecting more 'juice' at 2400Ws. Although

unrelated (I think) the pack makes a subtle buzz/hum when recharging between

shots. Is this normal?

<br><br>

Any light anyone can shed on my questions is appreciated. I'm really enjoying

shooting with the pack and heads -- I just want to make sure its working like it

should. Thanks!!

Bob,

400ws to 1200ws is an increase of 1.5 stops. f/16 to f/22.3 is an increase of 1.3 stops so that looks pretty accurate.

1200ws to 2400ws and f/22.3 to f/32.2 also looks close, within 1/10th of a stop. You could put those small discrepencies down to metering technique, unless your meter was locked to one position on a light stand. Still those figures look consistent.

Since you haven't mentioned the ISO used, the meter to softbox front-screen distance or the model/size/interior fabric of Chimera softbox, it's difficult to say whether f/32.2 is reasonable.

It is true that a well baffled softbox like the Chimera will absorb some light.

400ws to 1200ws is tripling the power. But remember full stops require doubling the power. So to get a full two stops you'd need 4 times the original power or 1600ws. Double once from 400ws to 800ws, double that 800ws again to 1600ws.

See below.

400ws to 800ws is doubling the power so a full one-stop increase in your meter reading is accurate. Then another doubling of power from 800ws to 1600ws would be needed to get another full stop of power for a full two stops.

But ....in your case, you're going from 400 to 800 which is one full stop and then going from 800ws to 1200ws which is only another 0.5 stops for a total of 1.5 stops. 800ws to 1200ws is only adding another 400ws which is half of what is the needed 800ws to make the 1600ws total.

I hope this is clear. Measuring light is an exponential affair so to speak and not linear.

2 raised to the power of n (2^n) is the scale you need to learn/use/remember.

2^0 = 1

2^1.5 = 1.4

2^1 = 2

2^1.5 = 2.8

2^2 = 4

2^2.5 = 5.6

2^3 = 8

2^3.5 = 11

2^4 = 16

2^4.5 = 22

2^5 = 32

2^5.5 = 45

2^6 = 64

and so on ...

Notice how these match up on your aperture scale and very close on your shutter speed scale too.

Wow, that scale didn't turn out right.

How do I edit my post to fix it?