Can I maintain the same flash pulse duration but increase light with multiple flash units?

Question

I own a Yongnuo YN-560 III speedlite, and I found out that it lets me freeze motion (for example, a water splash) at 1/16 of its power. However, the amount of light at 1/16 is not enough to properly light the scene I'm shooting.

Is it possible to increase the amount of light by using more speedlites, while maintaining the same flash duration?

Answer 1

You are correct to observe that the reduced power is the key to your flash's ability to freeze motion. More flashes may work (see caveat below) but since more gear usually costs more money, here are some alternatives

Slow the Event

If you are recording water droplets, record them right after they form. It takes a few feet for the drop to "speed up." If you are recording the splashes, use a smaller object/ droplet at shorter height and increase your magnification. The overall appearance is the same but the liquid will move slightly slower. Slowing down the object may allow you to increase the power and commensurate flash duration. At 1/4 power many flashes are still faster than 1/10,000s

More power

You could try a more powerful flash unit. It might seem counter intuitive but the duration of the flash is more closely linked to the relative power (I.E. A flash whose 1/16 power setting is 5 watt-seconds will likely have a shorter duration than a flash whose 1/4 power setting is 5ws, at those respective power settings.) This is not a hard and fast rule, though, as many factors in the design of the flash circuit play into the duration of the flash.

Multiple Flashes If you have ready access to multiple flash units and do not mind the visual effect of multiple light sources (perhaps combine them under one diffuser?) if they are perfectly synchronous. I've seen delays varying between 60 microseconds and 100 milliseconds in flash sync systems but a couple hundred microseconds is fairly normal.

Here is a method to check the synchronicity of your flash units:

1. Set up the various flash units next to one another and block most their light output. For example, use a piece of cardboard with pencil sized holes.
2. Place a lit flashlight next to the flashes.
3. Darken the room sufficiently
4. Open the shutter for a long exposure and move the camera quickly and perpendicularly to the arrangement of flashes. For example, if the flashes are side-by-side on a table, move the camera up and down. This can be accomplished by carefully swinging the camera in an arc.
5. Trigger the flashes while they are in the camera's FOV.
6. Once you have the shot (it takes practice) open the image on a computer
7. There should be several dots or short lines representing the flashes and one long line representing the flashlight
8. Draw a line along or straighten the image to the flashlight line
9. Draw a line perpendicular to the flashlight line, intersecting your master flash unit.
10. However far "behind" the master unit the slave units are represents the delay.

Notes:

• Any movement is sufficient so this can be done by moving the camera or flashes. I've seen people put their flashes on a passing car, for example.
• In a photo instrumentation lab this test is done with a camera equipped with a scanning shutter (many DSLRs can be used with a scanning shutter)
• if available, use a strobe light which is set to a known frequency so that the exact delay is calculable
• If performing this test with a rolling shutter, the movement must be perpendicular to the read-out motion.
• There are variations on this experiment which involve dropping a ball bearing past a ring of flashes. This works well to identify synchronicity differences but only if the object you want to photograph is slower than a falling ball bearing :)

Answer 2

Yes.

Speedlights reduce the light output by turning the "power" off earlier. This way the time the flash is on is reduced, which results in shorter flash duration for lower power flashes.

Adding another flash will keep the flash duration the same but double the overall output.

You might as well increase ISO.

Answer 3

Yes, you can use four speedlights. I always used to use two flashes for water drops, connected by sync cords.

But if 1/16 power is not enough, then it sounds like the problem is that your distance to flash is too great, and you must not be using ISO. The YN-560 guide number at 1/16 power 35 mm flash zoom (for example) is GN 16 (feet, ISO 100, chart in flash manual). So therefore, for one flash, f/16 is proper exposure ISO 100 at GN16/f16 = 1 foot distance (which works for water drops).

Alternatives:

Four flashes would add 2 EV (changes 1 foot to 2 feet).
(2 flashes double to 1 EV, and 4 flashes double again to 2 EV)

Or much easier, ISO 800 using only one flash adds 3 EV.

I have a guide number calculator that can show all of this on my site at https://www.scantips.com/lights/flashbasics1c.html

I used two flashes at 1/64 power and f/16 and greater flash zoom, and exposure was pretty easy. In my case, the flashes were behind a frosted plexiglass sheet behind the splash. The two flashes with color filters were about 2 feet from the splash. Example at https://www.scantips.com/drops/shako/

Answer 4

You can use a more flashes, specially if you use high quality units (brand name) together with high quality sync cables (brand name) of exactly the same length, avoid at all cost the curled type, connected in parallel to the sync output of the camera.

That way you will get a synchronized flash burst from as many units as you want. You want the same resistance in every cable... the electron flow to travel at the same speed, high quality flashes are built to lower tolerances between units than the lower priced ones, so they will fire with the same delay from the time the get the signal; that it’s were most of higher cost goes, the brand names makers don’t want to compromise quality using cheaper parts and compromising their quality assurance.

Since it’s unusual to find good parallel sync extension adapters, you will need to make them yourself with as little wire as feasible for the number of connections (flashes you will be using). In order to make it, you will need use high quality low resistance wire and connectors, know how to do fine soldering and how to use of a resistance meter to ensure the quality of the soldering and wire so the resistance for each connection is the same to ensure the synchronicity of your flash burst.

Answer 5

Here's a link showing the flash duration of your flash: http://speedlights.net/2010/07/14/yongnuo-yn-560-speedlite-review/#Flash-Duration

As you can see, at 1/16th power the duration of the light output is 1/5,600th. At 1/8th power, the duration increases to a still very quick 1/4,600th. You can increase power output while still maintaining a very short duration time. You may not need another flash a 1/16th power, but instead use your existing flash at a higher power setting and smaller f/stop or lower ISO.

Answer 6

The power of multiple flash guns indeed just adds but since the relation of power to flash duration is not really linear (and usually spelled out in a table in the manual of the flash gun), you might be better off using a single stronger flash gun at a weaker setting than multiple weaker ones.

This is one case where using powerful old flashes intended for analog cameras in "automatic" or "computer" mode (where they can extinguish fast given a close reflective surface) can be useful. Independent from that, if you put the flash off-camera, you can place it quite closer than your camera, again reducing the need for power.

Here is a photograph using a GN40 (meters) flash: (that claims 1/1000 sec flash duration at full power down to 1/50000 sec in its specs, likely somewhat optimistic) with a +3 dioptre achromat closeup lens and a polarizing filter (mostly as a makeshift ND filter).

And here is the setup creating this magic taken from close where the drops photograph has been taken:

You see the flash and radio trigger and the flash is pointed to a good degree at a white background making it quash fast: the sink itself does not help a lot since its reflection is mostly—its not quite polished state notwithstanding—directed away from the flash.