Parole chiave: live cell imaging, DIC, polarizing microscopy, Phase contrast, oblique illumination
Definizione:Hoffman modulation contrast is an oblique microscope illumination technique that enhances contrast by converting optical gradients into variations in light intensity
TECHNOLOGY:
Hoffman Modulation Contrast was invented by Robert Hoffman in 1975. It is useful for generating pseudo-relief images of unstained and birefringent specimens (for example, live cells in plastic culture dishes). The technique involves placing a diaphragm with an off-axis slit in front of the focal plane of the condenser. This effectively illuminates the specimen with oblique illumination. At the back of the focal plane of the objective there is a plate (the Hoffman modulator) with three differently sized neutral-density regions - transparent (100% light transmission), gray (15% transmission) and dark gray (1% transmission). This is placed so that the slit aperture is aligned with the 15% transmission region. When light passes through various regions of the sample, light is refracted to different degrees passing either through the transparent, gray or dark gray regions of the modulator. This has the effect of accentuating differences in contrast. Polarizing filters may also be used in Hoffman Modulation Contrast systems to further enhance contrast. Images may appear similar to those obtained in DIC imaging. Unlike DIC, however, Hoffman Modulation Contrast does not use beam-splitting prisms. It can also be used with specimens not suitable for DIC (crystalline substances or living specimens in plastic culture dishes). Hoffman Modulation Contrast imaging also avoids halos sometimes observed in phase contrast imaging.
APPLICATIONS:
Hoffman modulation contrast is used to enhance contrast in both stained and unstained specimens.
MICROSCOPE CONFIGURATION:
Nikon's TS100 and TS100-F and Ti series inverted microscope may be equipped with a Hoffman Modulation Contrast objective and Hoffman Modulation Contrast slider.
Specialized objectives for Hoffmann Modulation Contrast include:
The CFI HMC 10x (N.A. 0.25; WD: 6.2mm), CFI HMC LWD 20x F (N.A. 0.4; WD: 3.1mm), CFI HMC LWD 40x C (N.A. 0.55; WD: 2.7-1.7)
RECOMMENDED SYSTEM:
For the most versatile live cell imaging microscope system, Nikon recommends its Ti series inverted microscopes.
* Hoffman Modulation Contrast and HMC are registered trademarks of Modulation Optics, Inc.