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I've been dabbling with Water droplet photography for a while now so this information is based purely on what I've discovered works for me. It also assumes you are using a dSLR with free standing flashguns.
It is possible to take reasonable images using cameras with in-built flashguns but they are very restrictive and, with very few exceptions, will only produce photographs of average quality.
Please don't blame me for this limitation, it is just a fact of life
The current setup for most of my water droplet images is shown below.
There are several ways of shooting water droplets but they generally fall into three methods:
1. In a totally dark room using the 'bulb' setting on the camera. The flash guns are then fired independently from the camera when the droplet is hopefully in the right place.
2. In a room with subdued lighting you can trigger the camera which fires the flashguns. The camera shutter should be set to the fastest speed that it will still synchronise to the flash guns, this is typically 1/200 - 1/250 second. I tend to use this method unless I am shooting extremely high speed images where the mechanical delays in the camera would mean missing the photograph.
3. Use a fast shutter speed with the lens aperture wide open and the iso rating cranked up. With a few exceptions photographs taken this way will be crap. Add some some very high powered lamps, say 500w or more, and reasonable images can be achieved and you will stay warm on a cold winters evening.
It is important to understand that in methods 1 and 2 it is NOT the camera shutter speed that is freezing the droplet movement it is the flash duration that does the work. In a completely dark room the shutter could be left open for minutes and a frozen image will still be taken if you are using flash.
The rest of this tutorial goes through the method shown in 2 above but the information applies to most techniques.
The Canon 1D MkIIN or a 40D cameras which I use are always tripod mounted to give me the maximum sharpness. To avoid cropping the image I also use a 100mm or 150mm macro lens which is focussed manually.
The camera should be set to use the 'mirror lockup', if possible, for two reasons:
a. The mechanical delay of the mirror flipping up and then shutter firing is typically around 50 milliseconds so I lock the mirror up before each shot to reduce the delay down to around 20 milliseconds. Some, but not all, dSLR cameras have this feature.
b. Using mirror lockup removes almost all of the internal camera vibration and maximises the image sharpness, so use it if you can. Mirror lockup is recommended for a lot of photography styles including landscape/waterscape and nature photography.
I also use a cable release either manually or electronically fired. Used manually you are relying on practise and luck to get the timing right, using electronics to trigger the camera removes a lot of the uncertainities.
The camera is in manual exposure mode typically 1/250 second at f16-22 iso 100. I could stop the lens down further to increase the DoF BUT the images with the aperture fully closed to f32 are softer than at f16-22 due to diffraction limitations of the lens. This is common to all lens and using the smallest aperture for photography to get the maximum depth of field is not normally recommended.
On the camera hotshoe is a wireless transmitter that triggers the flashguns I use, normally Canon 580Ex guns and a 550Ex gun. You can use a wired flash system if you like, I use wireless to reduce the number of cables running around.
The flash guns are set to manual control and typically run at 1/64-1/128 of full power to minimise the flash duration. If the flash guns are set to use full power the duration of the flash is around 1 millisecond (1/1000 second) this long flash duration will cause motion blur and degrade the final image, this is one reason why in-built flashes are a poor choice. Set to 1/128 of full power the 580Ex flashgun produces a flash that is only 1/30,000 of a second duration, that's 30 times shorter than the gun on full power!
To use the flash guns on 1/128 power AND still be able to take the photograph at f16 iso 100 the guns need to be very very close to the droplet. My guns are covered in clingfilm to keep them dry because they are only 100-150mm away from the splash. Remember the guns have to be very close or you will end up using a wide aperture (small DoF) or a very large iso setting (more noise).
I use small lumiquest softboxes on the flash guns to soften the shadows they produce or if I want dramatic lighting some simple rolled up tubes of paper to make the flash very directional.
A small eye dropper or drinking straw can be used to produce the droplets, you can even use electrically timed solenoids valves to improve your success rate.
Food colouring is a simple way to dye the water to produce colourful photographs.
Coloured card or acrylic for background colour
Electronic timing and trigger systems are available that remove a lot of the difficulties of getting good water droplet images. I use infrared trigger beams that control the solenoid valves and the camera and flash guns.
The electronic control I have allows me to get the timing very repeatable once I find a droplet shape I like. Once I have the timing set correctly I can concentrate on the lighting arrangement and keep repeating the shot until I'm happy with the result.
Plenty of patience and imagination.
I'm getting a hit rate of about 80% so if I take about 50 images, 40 of them will be reasonable photographs, 1 or 2 of them I will keep.
The flash duration is around 1/20,000-1/30,000 of a second, if you dial the power down, and it is this flash duration that freezes the movement of the droplet NOT the shutter speed of the camera.
The ambient light of the room can cause motion blur on the droplets so subdued lighting or no lighting is recommended.
A low iso setting is also used to minimise noise and to reduce the effects of the ambient light.
A small aperture of f16-f22 will give you a reasonable depth of field.
Rather than colour the water you are dropping into use colourful backgrounds and photograph the colourful reflection of the background.
This type of photography can be achieved using normal high powered studio lights but it does need to be very high powered as you are reliant on the camera shutter speed to freeze the droplet movement rather than the flash duration.
If you have any questions/thoughts just shout and I'll try my best to answer them.