Measurement Of Chromatic Aberration Research Articles

Measuring chromatic aberration in LEEM/PEEM

Measurement of chromatic aberration in a Low Energy Electron Microscope (LEEM) or Photo Electron Emission Microscope (PEEM) is necessary for quantitative image interpretation, and for accurate correction of chromatic aberration in an aberration-corrected instrument. While methods have been developed for measuring the spherical aberration coefficient, C3, measuring the chromatic aberration coefficient, Cc, remains a more difficult task. Here a novel method is introduced to simplify such measurements. The viability and accuracy is demonstrated using detailed electron-optical ray-tracing calculations. Experimental results show that the method is easily reduced to practice.

Measurement of chromatic aberration in STEM and SCEM by coherent convergent beam electron diffraction

A simple method is described for the accurate and precise measurement of chromatic aberration under electron-optical conditions pertinent to scanning transmission electron microscopy (STEM) and scanning confocal electron microscopy (SCEM). The method requires only the measurement of distances in a coherent CBED pattern and knowledge of the electron wavelength and the lattice spacing of a calibration specimen. The chromatic aberration of a spherical-aberration corrected 300 kV thermal field emission TEM is measured in STEM and SCEM operating modes and under different condenser lens settings. The effect of the measured chromatic aberrations on the 3 dimensional intensity distribution of the electron probe is also considered.

Chromatic Aberration Classification Technology of Ceramic Tile Base on Computer Vision

The defects of artificial detection influenced the chromatic’s classification result of ceramic tile. In this paper, a kind of image registration method in space field is presented based on computer vision to match the ceramic tile. Then, CMC color algorithm based on CIELab color space is used to detect the chromatic aberration of ceramic tile. The experimental results indicate that the method of chromatic aberration classification technology used in this paper can recognize and classify ceramic tile with a high degree of precision. In addition, the measurement speed is improved and can meet the requirement of measurement of chromatic aberration on line.

Chromatic aberration and optical power of a diffractive bifocal contact lens.

Although diffractive contact lenses have been well documented in theory, no definitive experimental data have been reported which confirm that the near image is in fact created by diffraction rather than by refraction. We have tested the diffraction hypothesis for one type of diffractive contact lens (the Hydron Echelon bifocal) experimentally by measuring its longitudinal chromatic aberration in isolation and when worn on the eye. The basis of this test is that, according to theory, diffractive lenses should have chromatic aberration which is opposite in sign to that measured for the eye. Objective measurements of chromatic aberration were made with a focimeter when the lens was in a wet cell. Subjective measurements were made with a Badal optometer when the lens was worn on the eye. Four control experiments were conducted to provide baseline measurements of the eye's chromatic aberration, against which we compared the results obtained for the diffractive contact lens. The data were also compared with conventional measurements of refractive error obtained by standard subjective techniques and by an automated infrared refractor. Our results showed that the longitudinal chromatic aberration of the diffraction image of the Echelon bifocal lens was about one-half that obtained under the four control conditions: for the naked eye, for the nondiffraction image of the Echelon lens, or for either image of a refractive bifocal contact lens (CIBA Bisoft). These results are consistent with the theoretical prediction that the negative chromatic aberration of a diffractive contact lens should partially cancel the positive chromatic aberration of the human eye.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of age on the chronatic aberration of the eye.

The axial chromatic aberration of the eye was measured in 58 persons varying from 10 to 80 years of age. It was found that the chromatic aberration diminished significantly after the onset of presbyopia. It is suggested that this decrease in axial chromatic aberration may be due to increase in the index of refraction of the vitreous thereby producing a negative optical surface in the eye which more or less cancels the chromatic aberration of the cornea and anterior surface of the lens. This supposition is supported by measurements of chromatic aberration made on 10 aphakic patients. It is also observed that at near, older eyes who exhibit very little chromatic aberration, cannot make use of this aberration to spare some of the required accommodation (simulated by ophthalmic lenses in older eyes) as is the case in younger eyes.

The measurement of chromatic aberration on the hilger lens testing interferometer

An account is given of the experimental determination of the longitudinal chromatic aberration and secondary spectrum of telescope object glasses, using the Hilger lens testing interferometer. The amount of mirror displacement necessary to give the same interference pattern for different wave-lengths of light is measured by a screw micrometer.