Focus | Focus

Key Words: confocal, contrast, chromatic aberration, Resolution, spherical aberration, parfocal

Definition:The plane or point at which an image is most clear and well defined

TECHNOLOGY:

Users can manually adjust the microscope focus of their image using the coarse and fine focus controls (usually situated at the side of the microscope body). Focus may need to be adjusted following a change of objective magnification, addition of reagents, specimen movement, and temperature or vibration-related changes in microscope.
 
The accuracy and stability of focus depends on the optical system, the quality of optical components and the quality of microscope construction. The quality of the objective lens is particularly important (for example, parfocality and the ability to correct for aberrations caused by the passage of light of different wavelengths and curvature of lens components). Quality microscope construction is important in resisting vibration and temperature induced changes that could influence focus.
 
The microscopy imaging technique may also have an impact on focus. Widefield imaging projects out-of-focus light just above and below the plane of focus, which can blur the final image. Confocal imaging eliminates this out-of-focus interference using pinhole / slit technologies.

APPLICATIONS:

Correct focus is a universal requirement for all imaging applications.

MICROSCOPE CONFIGURATION:

Whatever the type of microscope, sharp focus depends on the correct set up and alignment of all optical components in the system (for example, objective and condenser, light source, optical tube length, coverslip thickness, immersion media). Dust, condensation, oil smears or other faults in any of these components can distort light and compromise image quality. A wide variety of objectives are available that are corrected for aberrations.

RECOMMENDED SYSTEM:

For live cell imaging, Nikon's TiPFS (perfect focus system) inverted microscope with confocal system (EC1, C1, C1si, LiveScan Sweptfield) and Plan Fluor, Super Fluor, Plan Apochromat and Plan Apochromat VC (for fluorescence imaging) objectives. All Nikon Plan Fluor and Plan Apochromat objectives are also suitable for DIC. PFS offers automatic and continuous focus adjustment in response to minute changes in the microscope set up and cell motility during time-lapse imaging applications.

LINKS:

Focus and alignment of mercury and xenon arc lamps: [microscopyu]