So the important thing is to focus the camera first with a very wide aperture, then set the aperture second. By doing this you reduce the depth of field so when you adjust the focus of the camera you can get it very finely tuned (as with a narrow depth of field any slight error in the focus will be more obvious).
Set the aperture second - this is where DigiFlow comes in. There is a function in DigiFlow that can help with this as it can be used to show the saturated pixels at twice the brightness of all other pixels, making them easier to see.
Focusing the Camera
This applies to the sort of camera you would use for experiments (it should preferably be on a tripod so you know you aren't going to move it afterwards). The trick is to reduce the depth of field so that it will be easier to see when the correct focus is set up.
- Turn off any projectors or high intensity light sources.
- Open the aperture all the way.
- Put something in the tank and focus the camera on this.
- Now turn on any light sources and adjust the aperture as appropriate.
Setting the Aperture Using Digiflow
Correctly setting the aperture ensures that the full range that the camera is able to sense is used.
- Turn on appropriate light sources.
- Open up a live view.
- Set the colour scheme to 'left single cycle - aperture'. (View > Colour Scheme or shift+ctrl+B). This sets the intensity of all pixels to half observed, unless that pixel is saturated, making it easier to see saturated pixels.
- Set the aperture such that a few pixels are just saturated.