Nude photos, like fashion, can present a challenge to getting crisp shots. The model moves, the pose is fleeting, and you may frequently change camera position. All these factors can lead to motion blur. The first ingredient to sharp photos is to have plenty of light. This could mean shooting with daylight or powerful studio strobes. A large quantity of light allows you to use a smaller aperture, yielding a sharper result from your lens.
In daylight, more illumination translates into faster shutter speeds for stopping motion. To avoid camera shake indoors or out, you should use a tripod (also see “Available Light”). In the studio, stopping motion depends on flash duration. If you are accustomed to camera-mounted flashes, you may think that all flash lighting will freeze motion. However, once you begin to use more powerful units, you will find that the flash duration can be as slow as 1/100 of a second. This is not fast enough to freeze quick action such as a model leaping into the air, dancing, or flinging her hair. Flash duration is measured in terms of t0.5 and t0.1, being the time required for the strobe to emit 50% and 90% of its light, respectively. For example, a flash may have a t0.5 of 1/1000 of a second and a t0.1 of 1/300 of a second.
The number you want to pay attention to is t0.1. Unfortunately, many manufacturers only state t0.5, do not indicate which measurement of duration they are using, or omit the information altogether. I recommend a t0.1 of no longer than 1/500 of a second if you are planning to photograph a moving model. If the manufacturer does not specify that the stated duration is t0.1, you can look for a duration of 1/1500 of a second, and assume that this is the t0.5.
As if that was not complicated enough, there are some more twists. Each flash’s duration is affected by its power settings. The advertised action-freezing duration is usually at the unit’s lowest power setting. If you are working with a wireless transmitter, you will be limited to the sync speed of the transmitter, which could be lower than that of your camera. On my website (www.nudephotoguides.com/resources), I include some specific equipment recommendations. To find the sweet spot of your lens, take a variety of shots at varying settings. After you determine the sharpest frames, look at the shutter speed and aperture settings that are recorded in the EXIF data.
This article is from the book, True Confessions of Nude Photography
A few flash units I’ve found that achieve fast flash durations and respectable power output. Many of these can be purchased used for those on a lower budget.