Differential Interference Contrast Specs

1. DIC prisms and sliders

• Each DIC objective needs its own prism slider and cannot share across magnifications

• Wollaston or Nomarski type prisms are both common

• Sliders should allow fine prism adjustment for shear amount and background colour

• Objective turret positions must match slider slots, otherwise a magnification is unusable

• Note: prisms and objectives must be bought as pairs, since buying objectives alone is a common error

2. Polarising optics

• Polariser below the condenser and analyser above the objective, set strictly crossed

• Rotatable polariser for brightness and background control, with the analyser fixed or rotatable

• Full wave or quarter wave compensator for sensitive tint adjustment

• Polarising elements should be calibratable with the crossed position repeatable

• Note: without a strict crossed setting the relief disappears and the image looks flat and grey

3. Objective matching

• DIC dedicated or strain free objectives only, since ordinary objectives cannot form proper relief

• High aperture objectives give larger shear with strong relief but limited tolerance to thickness

• Low aperture objectives give smaller shear and suit fine structure

• Long working distance DIC objectives for dishes and multiwell plates

• Note: DIC demands more of the objective than phase contrast does

4. Shear amount and relief

• Shear set by prism specification, with adjustable types preferred

• Relief direction adjustable by rotating the prism to match structure orientation

• Background colour adjustable through prism position for different detail emphasis

• Note: excessive shear creates an artificial three dimensional look that hinders interpretation

5. Sample and vessel limits: the key item

• Plastic dishes and flasks are birefringent and produce strong interference colour, so they cannot be used

• Glass bottom dishes or coverslip chambers are required

• Samples should be thin, ideally 10 micrometres or less, to avoid overlapping structures

• Best suited to live cells, unstained specimens and transparent material sections

• Note: plasticware is the most common failure point in DIC, so confirm consumables first

6. Comparison with phase and brightfield

• DIC has no halo and gives an optical section look suited to surface and fine structure

• Phase has halo and suits low contrast transparent samples but with less detail

• DIC performs better on thicker samples, with both similar on thin ones

• DIC optics are more complex and costly with higher light loss

• Note: DIC and phase can complement each other on one stand depending on the main samples

7. Illumination and imaging

• Polarised light path costs significant flux, so a high output source is needed

• Sensor of 5 megapixels or more with a bit depth of at least 10 bits

• DIC images look grey overall, so keep raw data for later enhancement

• Trinocular splitting should serve viewing and imaging at the same time

• Note: the relief comes from phase contrast created by optical path difference, not true 3D reconstruction

8. Operating environment

• Vibration isolation, since DIC is sensitive to small displacement

• Stable temperature, because thermal drift shifts the path difference and background colour

• Dust and moisture protection for polarising elements, with prisms stored in dedicated cases

• Regular calibration of the crossed polariser and analyser positions

9. Where procurement goes wrong

• Buying DIC objectives without matching prism sliders, leaving half the magnifications unusable

• Using plastic dishes for live cell DIC, where interference colour swamps the sample

• Fixed, non adjustable polarisers that cannot be returned to crossed position once drifted