Setup to photograph the milk drops

A 12 milliliter "cow syringe" is very good to use for milk drop photography. It is shown below, and is about 50 cents from a feed store - for doctoring animals, but no needle used here. Buy two or three, they eventually become sticky. The syringe is used to release the drop, from a fixed mounting point, to always fall in the same place. The drop falls through a LED interrupter gate which interrupts the circuit, starting the timer, which eventually triggers the flash. The Nikon SB-800 flash unit at 1/128 power works great for this (manual mode from a few inches), as should any other speedlight at low power.

A timer gives repeatable and consistent timing, which is very good for milk drop splash photos, because the splashes give very different (but repeatable) patterns at different points in the duration of the splash. The entire splash is over in only a very few milliseconds, but it first produces the crown (best falling on a thin film of milk), followed by a central rebound column (best falling on a deeper pool of milk), and each stage has phases, start, middle, end. No two splashes are exactly the same, but the timer can easily and repeatedly capture the same moment. You just set the timer to produce which ever point in the splash that you want to photograph. It is a bit touchy to adjust just right, but not hard. There are other parts that are harder, for example the collision of the rebound and the next drop is nearly impossible. :)

The timer board used for these photos is shown hanging with the syringe just for this photo, but it is not normally put up there. You can see a round drop of water falling in the black gate, which triggered the flash for this photo, with zero delay setting. A longer delay let the milk drop fall 24 inches for the photos before. The blue variable resistor in lower left adjusts timer delay time to fire the flash, which you adjust to give the delay result desired, judged in a photo in the camera LCD.

You use manual focus and manual flash and manual exposure of course, so a DSLR seems necessary. I focus on the spot where the milk drop will be later by temporarily putting something there where it is hit, so I can focus on that spot - like a screwdriver blade or a bent piece of heavy wire that extends to the same spot where the drop lands. The camera shutter lag is much longer than the duration of the drop splash, so after focusing, open flash is used in a halfway dim room. Set the shutter speed to Bulb, hold the shutter open, release the milk drop, the flash will be triggered, and then close the shutter. This takes a second or two of open shutter, so I add the camera's Long Exposure Noise Reduction setting (however I don't see any actual need for it).

The room is dim, but not dark. I leave one table lamp on "low" across the room, and still get a black frame without the flash (at f/16). I do turn on extra light to focus. In manual focus mode, the Nikon D70S viewfinder green LED still indicates correct focus, if you hold the shutter half down. I use a Nikon 60mm macro lens very near its minimum focus distance, with a clear UV or Skylight filter to protect the lens from splashes. It will get wet, so I wish for a longer macro lens. I often place an 8x10 inch picture frame glass standing up in front of the lens, to shield it - I cannot tell that it has any bad effect, but it must be cleaned often, which is of course the point of it.

The flash is triggered directly by the timer PC cable (neither one connects to the camera). Adjust distance of the flash so the milk exposure does not overflow your histogram on the right... a bit darker usually gives better looking milk drops. The Nikon SB-800 at 1/128 power (24 mm wide zoom setting) placed from 7 to 10 inches is about right for f/16 and ISO 200. Minimum flash power is both necessary and sufficient.

I found it convenient to make the mount shown above, to locate the syringe so the splash falls in the same place every time for the camera. It is simply just a piece of sawed PVC pipe to locate the round syringe, glued to a clear plastic plate with hot glue, screwed to a 3/8" aluminum rod (slightly flattened with a file), held by an umbrella mount in a light stand. Or a clamp on a labratory stand should work fine too.

The timer is the SPG2-DU-BB kit (Schmitt trigger photogate-delay unit combination with breadboard), from HiViz . Price is $18 USD plus shipping. It is a kit, so you must do the wiring, but easy and detailed instructions are available online there. It is a real bargain, and it works very well for high speed milk drop photography. Also see the Guidebook for High Speed Flash Photography there. Very interesting site.

The SB-800 has a PC cord connection, so I bought a cheap male-to-male PC cord, which when cut in half provides two such cables for the timer (they offer a similar timer triggered by sound too).

I found one error in the timer wiring instructions, where the instructions didn't match the schematic. My opinion is that the schematic is correct, and produces correct results.

Specifically, the wiring instructions (at step 4, 2nd paragraph, 4th sentence) shows the timing capacitor (0.47-µF electrolytic capacitor) attached to pin 3 of the 556 chip, which then goes to ground through the 0.05 capacitor (top right corner of the schematic). However the schematic shows the node of C and the 0.05 capacitor is at ground and not at chip pin 3. That is, C should be located at the other end of the 0.05 capacitor, at the ground end. So to correct this, pull out the row 25 pin of C, rotate it around, and that pin should instead go to row 29, column i, which is ground (instead of "row 25 of the same column", which is incorrectly at 556 chip pin 3). Compare yours to picture above.

If wired to agree with the schematic, the maximum delay is up to perhaps 1/2 second (other values possible using other furnished resistors), same as the expectations stated in the paper. If wired as per the wiring instructions, there is possibly some tiny delay, but only a fraction of expected. This very short delay is what caused me to look closer at it. This has been reported long ago, but it was never corrected. But make that little change, and it works great.

As to the lighting setup, don't mix fast and slow lights when the goal is speed. I discovered an interesting problem when I tried that. :)