Introduction to Hoffman / Relief Contrast
Relief Contrast is exactly Hoffman Modulation Contrast (HMC), with a minor difference that Zeiss and Leica uses Hoffman Modulation Contrast (HMC) term but Olympus calls is Relief Contrast (RC) and Nikon names it Advanced Modulation Contrast (AMC). Regardless of the name, this is an imaging technique for enhancing the contrast. Like normal phase contrast imaging a biological specimen does not required any staining. Robert Hoffman originally invented the technique in 1975. Like differential interference contrast (DIC) technique, contrast is increased by using components in the light path that convert phase gradients in the specimen into differences in light intensity that are rendered in an image that appears three-dimensional (3D). The 3D appearance of a specimen may often be misleading because a feature that appears to cast a shadow may not necessarily have a distinct physical geometry corresponding to the shadow. HMC systems typically consist of a condenser with a slit aperture, an objective lens with a slit aperture, and a polariser that is fitted between the condenser and the illumination source and is used to control the degree of contrast.
The Relief Contrast or Hoffman Contrast technique is particularly suitable for optical sectioning at lower magnifications. Max 40x magnification is available in the market.
An example of the use of HMC illumination is in in-vitro fertilization, where under brightfield illumination the near-transparent oocyte is hard to see clearly. Reference: Three-dimensional culture of human meniscal cells: Extracellular matrix and proteoglycan production, Helen E Gruber, David Mauerhan, Yin Chow, Jane A Ingram, H James Norton, Edward N Hanley and Yubo Sun, BMC Biotechnology, 2008, 8:54, doi:10.1186/1472-6750-8-54
|Normal Phase Contrast|
Relief /Hoffman Contrast