Key Words: confocal, finite optical system, chromatic aberration (axial), apochromat, infinity optical system
Definition:Lateral chromatic aberration is a phenomenon where image aberrations both in size and color appear towards the image periphery and progressively worsen with increasing distance from the image centre
TECHNOLOGY:
Even when a microscope objective brings all three main colors to identical focal planes axially (as in fluorite and apochromat objectives) image details near the periphery of the field of view may be distorted because off-axis rays of light are dispersed causing component wavelengths to form images at different heights (chromatic difference of magnification). This results from an increase in the refractive index of all common materials towards the blue end of the spectrum. Lateral chromatic aberration differs from axial chromatic aberration in that axial aberration can occur anywhere in the image, while lateral aberration occurs at the image periphery. Both may occur simultaneously.
In older microscopes with a finite optical system, a compensating eyepiece may be used to correct lateral chromatic aberration. This compensation is not necessary with infinity corrected objectives and microscopes. Today's objectives are corrected for lateral chromatic aberration either as in inherent part of the lens design or in the tube lens.
APPLICATIONS:
Chromatic aberrations (both axial and lateral) can be a nuisance in all imaging applications but are most significant when trying to determine the relative distributions of multiple fluorescence and other colored probes in cells and in color photomicrography.
MICROSCOPE CONFIGURATION:
Selection of appropriate objectives is critical to minimizing chromatic aberration and to obtaining reliable results, especially in confocal imaging. The choice of objective will depend on the specific application, imaging conditions, and fluorescent probes used.
RECOMMENDED SYSTEM:
Please consult your local Nikon representative for advice relevant to your application. In Nikon's CFI optical system, both axial and lateral chromatic aberration have been corrected independently in the objective and the tube lens to produce flat images with excellent color reproduction. Nikon's CFI Plan Apochromat objectives are designed to correct all optical aberrations throughout the visible spectrum from violet to red, and from center to edges across the entire 25mm field-of-view. In addition to the correction range of the conventional Apochromat series (435-660nm), axial chromatic aberration has been corrected up to the violet range (405nm) in Nikon's Plan Apochromat (VC) series objectives. These objectives are highly effective for PA-GFP, as well as other photo-activation and photo-conversion proteins that activate at 405nm. They are ideal for multi-stained, fluorescence specimens and when using brightfield and DIC techniques. Plan Apochromat (VC) series objectives are also vignetting-free - the resolution of the objective lens is even across the entire field-of-view making it useful for digital photomicrography.