The main features to look for in a battery-powered monolight are output, recycling time, output range, number of pops per charge, modeling light power, types and sizes of modifiers, size and weight, and price. Monolights tend to be less powerful than studio strobe power packs and heads, but the improved ISO capabilities of modern DSLRs are mitigating that power differential. At the same time, monolights give you access to all of the sophisticated modifiers of a studio strobe outfit.
Output. More powerful units give you more options for depth of field (you can shoot at smaller apertures), light placement (you can place lights farther away if you have to, as for outdoor sports action) and use of light modifiers like umbrellas, which reduce intensity. Some units are rated in watt-seconds (W-s), others in joules; one joule equals one watt-second. Note that joules and watt-seconds are measures of generator power, not necessarily light output; output also depends on the flash head and any light modifiers used.
Guide numbers aren't really useful for pro flash because they're based on point-like light sources that follow the inverse-square law (double the flash-to-subject distance and quarter the light, triple the distance and get one-ninth the light, etc.), like shoe-mount flash units. Pro units are generally used at close range and/or with umbrellas or other light modifiers that increase the size of the light source relative to the size of the subject, where the inverse-square law isn't a useful measuring stick. Some pro-gear manufacturers include the tested ƒ-stop for a flash head (or head with specific light modifier) at a specific distance, which can be a useful comparison measure if another manufacturer provides the same data for its units.
Output Range. Monolights can also be operated at a range of power settings. This is helpful not only when you want to control light output, but to control flash duration (lower power generally means shorter duration), battery life (full-power bursts take more out of the battery than lower-powered flash) and recycle times (the flash will recycle more quickly at lower power settings). Because they're self-contained, you can adjust the power of each unit separately in a multiple-light setup for easy control of lighting ratios. Color temperature can change with power setting, although with today's units, this generally isn't a big problem.
Pops Per Charge. Battery power is a critical limiting factor. When comparing potential purchases, note how many full-power flashes the unit can produce on a full battery charge. Also check into the cost of extra batteries and how long it takes to charge them fully.
Location Lighting Masters
|Crafting the light for a photo is an art, and it's also an exercise in puzzle-solving. Two photographers you should follow to learn both the art and the puzzle-solving sides are David Hobby and Joe McNally. Hobby is the founder of the popular Strobist blog, and McNally is widely known as one of the most innovative location lighting masters in the world. As much as we focus on the light head in this article, it's knowing how to manipulate the light that really creates the style, look, mood and emotion in the photo. David Hobby's Strobist blog is at www.strobist.blogspot.com, and Joe McNally's website is at www.joemcnally.com.|
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