A few scanning tips


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. This will do anything you could want for one water drop.

However, two water drops, for example the collision of the rebound and the next falling drop, is really difficult (at least for me with only this timer). It is done, some can do it with a single timer, but you need a way to release multiple drops (a dripping spigot valve), and some luck. A fancy timer that can also time a solenoid valve releasing two drops makes it very easy.

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 (two pages back here). 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. Then it is very repeatable, every shot is timed right.

I found it convenient to make the mounting shown above, to hold the interrupter (the gate for water drops), and to locate the syringe so the splash falls in the same place every time for the camera. It is simply just a piece of PVC pipe sawed length-wise 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 bracket on a light stand. Or clamping to a labratory stand should work fine too. You probably want the splash from a milk drop that has fallen 12 to 18 inches.

You use manual focus and manual flash and manual exposure of course, so a DSLR seems necessary (and a macro lens). 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 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 near its minimum focus distance, with a clear UV or Skylight filter to protect the lens from splashes. It will get wet, a longer macro lens would be better. 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. I use a shutter release cable or remote, but the flash is still very fast without it. The camera shutter is opened manually in Bulb setting, then the drop is released (two hands). After the drop triggers the flash, then the shutter is closed manually. The fast flash duration stops the motion, and the dim ambient room light does not register at the f/16 aperture, even when the shutter is open a couple of seconds (verify this result is black once, without the flash). Adjust exposure with the distance of the flash, so that 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. 1/64 or 1/32 power will work too, but a minimum flash power is both necessary and sufficient. Adjust timer delay for the splash result you want to capture. This adjustment becomes easy after the first few minutes of experience, you will know about where it should be.

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 (and come with it). 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.

For reference, here are the board wiring instructions and the gate wiring instructions, and the schematic. The schematic may be a mystery for some, but you will be able to do the wiring. Click on the photos in the left column of the instructions - especially the last one to see it. You just poke those little thingies into the holes it describes. Do it like it says and it will work. The timer provides adjustable flash delay up to about 1/2 second, and extra resistors are furnished for longer times too.

The flash sync cable is not included. The flash has a PC cord connection (there are inexpensive foot adapters to add a PC connection if it doesn't), so I bought a longer cheap "PC male to PC male" sync cord, which when cut in half provides two such cables, for two kits (they also offer a similar timer triggered by sound too). The half should reach from timer to the flash. Or it may be easier to find a short "PC Female to PC Male" cable (which is an extension cable), and then just cut off the wrong male end (wrong to serve as an extension cable), so that this short soldered female end can accept your existing regular flash cable (which is male itself). The timer also needs a regular 9V battery, which will last many days of use if you disconnect it when not in use.

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. :)

Copyright © 2007-2010 by Wayne Fulton - All rights are reserved.

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