I suppose I should have dialed in the ws on the Topas to equal those on the Visatec (the Topas has digital controls in .1 stops.) Instead I dialed down each unit by a full 1 stop each time, starting at full output.
Anyway, you can see that the Visatec output at 300 ws was 5.6 + .5. That is about .8 stop below the 400 ws output of the Topas. It **should** be only .3 stop lower if the outputs were equal at 400 ws.
In other words, the pack is putting out about .5 stops more light than the monolight is at the same ws rating.
These results should be easily repeatible. I measured at least 5 times at each power setting. The readings were exactly on each time.
The output is stable within .1 of a stop for most of the area covered by the softbox. When you get out to the corners it starts to fall off by .1 stop. It should be easy to find the center spot of the softbox to repeat the test in your own setup.
The results are a little more sensitive to distance. But it is not a problem to repeat the distance measurement with .1 or .2 accuracy using the digital distance meter. You would have to go from 10\' to 14\' to reduce output by 1 full stop.
You can see that the results were exactly at a 1 stop reduction on the meter when reducing power by an indicated 1 stop on the controls for each unit. That has always been true for all of my digitally controlled units. It might vary a bit more for the dial or slider (POT) controlled units.
I have 7 more types of packs and 2 more types of monolights I could measure. It will take me a while though, I have a lot of other work right now that I need to finish first.
I don\'t have an AB monolight or any Profoto lights, two units that I am sure folks would be interested in seeing results for. I\'d like to see what kind of measurements folks get if they do this test.
Best,
M.
Dec 05, 2008 at 10:15 PM
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