The Profoto B1s are the battery operated smaller brother of the Profoto D1 monoblocks. One major advantage they have over their AC counterpart is that you can freeze super fast motion much easier than you can with the D1s. Suspending motion with strobes has everything to do with flash duration, and as I learned today, the Profoto B1 heads have a special mode called Freeze Mode that can make your flash duration even faster.
The first time I really became aware of flash duration was years ago when I did my Wakeboard Studio Shoot for Fstoppers. At the time I was using Dynalite power packs which were the first studio lighting system I invested in when I started my photography career. Unfortunately the Dynalite packs were not great at freezing fast moving objects. If you have not seen how I produced the images in the wakeboard studio shoot, you can view it on our youtube channel, but here below you can clearly see just how much of an impact flash duration can have on your images.
As I discovered, if your flash duration is too long, your strobes can actually act sort of like constant lights which are notorious for for producing blurry images when motion is involved. The motion in the water isn't a completely useless effect, I kind of like the action feel it gives the images, but if you want the sharpest images possible for still life, you will want to make sure your strobes release all their power in as little time as possible.
Recently Profoto shared a video with photographer Jared Platt who demonstrates exactly how to get the sharpest images out of your Profoto B1 and B2 lights. As a B1 owner myself, I knew that lowering the flash output also increased the flash duration (it's opposite with the studio D1s, you have to max out the power for the fastest flash duration). What I did not know was that you can set your B1s to give either a more accurate and consistent color temperature each time it fires OR you can set your B1 to give a much faster flash duration. These two options are described as Normal mode and Freeze mode.
How to Turn on Freeze Mode:
Setting the Freeze Mode option for your B1 and B2 lights is pretty simple. Turn on Freeze/Normal mode by pressing and holding the ENERGY/SETTINGS dial and then shortly press the TEST button. The text FREEZE should be displayed in the upper left corner of your LCD screen.
How the flash duration differs in each mode:
Regardless of which mode your flash is set to, you will always experience a faster flash duration (t.5 time as measured by Profoto) as you decrease the power on the unit. In Normal Mode, the t.5 time is 1/1000s at full power and 1/11,000s at the lowest power. If you switch over to Freeze Mode, you can get the same 1/1,000s t.5 time at full power but a crazy fast 1/19,000s flash duration at the lowest setting. The below graph shows the differences in flash duration (t.5 times) vs the power output for both Normal and Freeze Mode.
According to Profoto's website, if you do set your B1 or B2 to Freeze Mode, you can expect a flash color temperature change between +/- 50 Kelvin between each flash pop (Normal mode is only +/- 20 Kelvin per flash pop). If you are working with a single strobe or shooting without any ambient light, it might make the most sense to always shoot in Freeze mode since the color drift isn't that great and it can easily be fixed in post. However if you are photographing still life that does not demand freezing fast action and capturing accurate colors are a top priority, the Normal mode is probably the best setting. Normal mode is also preferred when mixing multiple flash heads since you want each unit to produce similar light when fired.
If you are still having trouble understanding how long flash durations could affect your images, our good friend Alex Koloskov at Photigy has made this very detailed review video showing how the Profoto D1s perform with liquid splashes. Alex is an amazing studio photographer whose work you can view here.