Pixiq

It is no secret that I had never taken a single photo until I was given my very first camera – an East German Exakta – for my 21st birthday. I was then working as a marine biologist and my favored subjects were marine organisms – both on the shore and in aquaria.  I have covered photography in public aquaria and in home aquaria in previous posts, when I touched on dark field illumination (DFI) but I am now going to explain it in more detail.

The biggest challenge with successful DFI is finding suitable subjects – preferably flattish ones that have an internal structure that is revealed by backlighting. DFI is a brilliant way of lighting any translucent objects – especially marine and freshwater life –- so that they appear to glow against a dark background. Intact or skeleton leaves as well as flowers, work equally well when laid on a sheet of glass raised up from the background.  

The aquaria sold in aquarists outlets are not suitable for this kind of photography since Plexiglas ones scratch easily and may have a company logo on the bottom, with is not always flat. So over the years, I built my own glass aquaria. The four walls are fixed with aquarium safe silicon sealant to a base that has flanges that extend out on each side so the tank can be supported above a table with enough room to angle a pair of small flash units up towards the base of the tank.

Originally, I used two small non-TTL flash units positioned with the flash windows angled  up towards the tank at 45º, making sure there was no risk of flare on the lens. Once I had worked out the exposure for 100 ISO, it did not vary much because as the magnification increased the lens was moved in closer to the light source, which compensated for the fall off in light with greater magnification. Now, it would be much easier to use a couple of small speedlights that come as part of the Nikon Commander kit, which can be triggered remotely via IR wireless communication.

The biggest problem with aquatic life is that every particle in the water shows up like a snowstorm when they are backlit, so it pays to filter the water. Below is a sequence of a marine blue prawn with a red alga scanned from an original transparency. 

 Firstly I adjusted the levels to brighten up the red seaweed and the prawn, Small particles can sometimes be eliminated simply by adding black to the black layer in the Selective Color Options in Photoshop, but you have to make sure that unwanted black is not also being added to the subject as well. Then I work at around 60% to remove the larger bits within the largest background area. The aim here is to get a plain black area as speedily as possible.  This can then copied with the Patch Tool and speedily patch up elsewhere.  I then worked at 200% or more to remove bits adjacent to the prawn or seaweed with the Clone Stamp Tool. It sounds tedious but with practice you soon speed up.

The final shot was cropped so that the seaweed no longer overpowered the tiny prawn, which I positioned diagonally in the frame with negative space at the left and top for copy. By then the file size was 24MB,  but was easily upsized using Genuine Fractals.

 Points to check

• Base of tank / sheet of glass is clean and scratch-free.
• Filter water before adding to tank.  This will save time removing the snowstorm effect of backlit particles in Photoshop.
• Remove any air bubbles in the water before introducing any livestock.
• Use a flashlight shining up from below the tank to focus and gauge the effect.
• If necessary, use another sheet of glass to flatten a leaf.