Oil, Water and Food Dye Pt3

As promised last time out, here are the more detailed guidelines for creating your own digital cooking-oil art using a digital background:

Select some background images to work with and display one on your laptop/ipad/etc screen. The image only needs to be big enough to cover the space under your water container. It should contain some bright elements as it will be back-lighting your image. Turn the laptop screen up to max brightness.
Place the laptop, with the screen in a horizontal position, under the glass table (as close to the table top as possible without touching). Do not place water-carrying objects directly onto computer screens - unless you're keen to splash out (sic) on a new computer!

Pour some water into your container. Amounts will vary, but generally I work with 1 - 4 inches of water. The depth of the water will influence how sharp or soft the background will be, since the oil floating on the surface will be the point of focus.
I have found lukewarm / room-temperature water works better than cold water - the oil takes longer to coagulate into a single bubble.
Dribble a small amount of cooking oil into the water and place the container on the glass table over the image on the laptop screen.

Position your camera on a tripod directly above the water. If possible, get close enough to fill the frame with the base of the container. The closer you are, the bigger the oil bubbles will look in the final images.
Try to keep the camera as level with the surface of the water as possible for maximum depth of field (zone of sharpness) across the frame; when working close up with wide apertures a slight tilt can throw areas of the image out of focus surprisingly quickly (you may want that, of course).
There are no hard and fast rules dictating the camera settings, so think of the following as a starting point:

ISO: 400 or higher, to accommodate the low light produced by the screen
aperture: wide open (e.g. f2.8), again to help with the low level of light; also helps keep the background soft, so it does not dominate
shutter speed: 1/60 second; you want the shutter slow enough to allow lots of light in, but fast enough to freeze the image if the oil is still moving in the water

You can try autofocus, but will probably find manual focus works best as autofocus struggles with this type of semi-opaque backlit subject.

You are now ready to shoot. Experiment with camera settings, distance between camera and water, depth of water, amount of oil, different backgrounds and so on.

If the oil coagulates into a single large bubble, give it a stir with a reed or coffee stirrer and wait a few seconds for it to stop spinning so quickly.

If there is too much oil in the water, tip it all out and just pour in some more water - plenty of oil will probably still be present.

Food Dye

You might also like to add some food dye. There are a range of colours cheaply available, but I find red works best for some reason - other colours seem to 'gloop' together into one big depth-charge, rather than produce pretty patterns. Food dye can also look good on its own against a plain bright background.
Shoot immediately after adding the food dye, and fire off a number of frames in quick succession; you can then select the best pattern or create a progression of images.

Printed Background

If you are planning to use a printed background, you will need to think about how you want to light it. Whether you use flash or a constant light source, you want to be able to direct the light onto the background without directly lighting the water. In other words, you will create back lighting, which will bring out the contrast and colours, so will need to keep some space between the table top and the background underneath.
A spotlight or flash with 'snoot' attachment will work best, but if you don't have that equipment, you can still block the light from the table top using black card (or similar).
You could also position your light source very close to the background, under the table. If you do that, you may need two lights - one from each side - to create an even spread of light across the background; even if the light only needs to cover a small area, the 'fall off' (drop in intensity) from a close-up light will be very rapid and may result in an unevenly lit image. For more information on this, check out the 'inverse square law'.

When using a strong light source such as flash, ISO 100-200 produces a less grainy image that the higher ratings recommended above. Set shutter speed to the flash sync speed specified in your camera manual.

Have fun.