Differential interference contrast

It begins with D, but it could easily also begin with J. I’m going to be as succinct as I can:

DIC-microscopy is like meeting Jesus Christ in the comfort of your own home.

Holy mother, when I turned on my microscope to use it for the first time I almost cried. Everything is so clear, classy and detailed. Every little detail of those microbes comes out to greet you. The small cogwheels of the universe turn in full splendour. What a spectacle!

Green biologist: OK Erik, I had enough. Why does not everyone use a DIC microscope?

Duh, it’s the economy stupid. DIC is really really expensive and the parts are super-rare. DIC is typically installed in high end microscopes and bought by pharma, tech companies or academic institutions with grant $$$ to spare. Parts from these microscopes drip out in a slow and limited stream on the second hand market.

First, the physics lecture. For DIC contrast to emerge, a lot of stuff needs to happen inside the microscope. Stuff that doesn’t happen by chance.

1. The incident light is polarised.
2. Incident light travels over a fancy birefringent crystal cut at a specific angle. This separates the light into two polarised components that strike the sample at slightly different (spatial) positions.
3. If these light rays then traverse portions of the samples with a refractive index gradient, a relative phase shift occurs between the two light waves.
4. The two rays are then recombined at the back-focal plane of the objective. Just like phase-contrast microscopy, DIC enhances differences in refractive indices and turn the phase change into… color.

Green biologist: Why is it so expensive then?

1. You need a frame that can house the components. Typically, it’s only one of the tier 3 frames like Nikon E800 or Olympus BX50/60 ($$$). DIC is very light-hungry, so microscope with a 100W halogen equivalent is needed.
2. You need a set of fluorite or apochromatic objectives ($$$).
   
   

   But wait, there is more…

   
   Depending on what make of instrument you have, you also need to shell out for the following.

    

3. A rare and obscenely expensive condenser known as “a universal condenser” ($$$)
4. A universal DIC prism ($$$), to be placed above (Olympus) or below (Zeiss, Nikon) the sample.
5. Objective-specific DIC prisms, which can only be used for a single magnification. If you are planning to use say 10x, 20x, 40x and 100x that means 4 different prisms ($$$).
   
   Unfortunately, it doesn’t end there…
   
   
6. You also need to procure a set of polarisers, which forms the first and last link of the chain. More often than not, one of these are rotatable which unfortunately adds $$$ to the final bill. And no, a pair of disassembled 3D-glasses won’t do. Get the brand name polarisers! And yes, you can use them for more than DIC.

Expect to shell out $1000 for the condenser (good luck finding one), $500-1000 for the universal prism and ($250-800) for the individual prisms, all on the second hand market. Did I mention that these things are also rare and hard to find?

If you have read this far, perhaps DIC microscopy is for you!

I wish you the best of luck in your endeavours. Come prepared, either with a big wallet or a big bucket of patience. But I tell you. It’s worth it!

You can read more my experiences with DIC for the Olympus BX system here.