Flat-fielding

No distortion, neither geometrical neither due to magnetic fields, thanks to proximity focusing. The non sensitivity of the tube to magnetic fields enables software enhancement of the images such as flat field corrections. 

Boron implant with laser anneal. Boron atoms are accelerated into the backside of the CCD, replacing about 1 of 10,000 silicon atoms with a boron atom. The boron atoms create a net negative charge that push photoelectrons to the front surface. However, the boron implant creates defects in the lattice structure, so a laser is used to melt a thin layer (100 nm) of the silicon. As the silicon resolidihes, the crystal structure returns with some boron atoms in place of silicon atoms. This works well, except for blue/UV photons whose penetration depth is shorter than the depth of the boron implant. Variations in implant depth cause spatial QE variations, which can be seen in narrow bandpass, blue/UV, flat fields. This process is used by E2V, MIT/LL and Samoff. 

Standard data reduction, i.e. bias and flat field correction, has been performed with Iraf. The Iraf task APEXTRACT/APALL was used to extract the spectra, with interactively selected background sampling, in order to avoid contamination for the star spectrum. The wavelength calibration has been done using daily He, Ne, HgCd arcs, and, in order to improve the calibration, wavelengths values for the transitions used were taken from http //physics.nist.gov/. 

Orion Constellation This is a mosaic picture of 18 (6x3) frames. Additional four frames are added around the Barnard Loop region to increase S/N. Vignetting of the telescope is corrected by flat fielding, using proprietary software written in IDL. Distortion correction and initial colour match is done in Registar, with final colour correction and mosaic processed using Photoshop. (Reproduced by permission of Wei-Hao Wang, Institute for Astronomy at University of Hawaii)... 

Figure 2.10 The flat-fielded Chandra image in the energy band 0.5-2.5 keV with a King model subtracted to remove the large scale radial surface brightness gradient. Many faint features are seen including 1) the prominent eastern and southwestern arms and their bifurcation (El, E2 and SI, S2 identify the extensions of the eastern and southwestern arms), 2) the 14 kpc (3 ) ring, 3) the 17 kpc (3.75 ) arc, and 4) the faint southern 37 kpc (8 ) arc.

In this case, dv is the Raman shift increment observable with a slit or pixel of width Wp. However, an array detector has a finite number of pixels, and the flat field of the spectrograph is of finite width, so there is a limit on the range... 

Double 8 850 0.1 0.012 [Pg.171]

The microscope body (Bausch and Lomb) has a four-objective revolving turret. Flat-field objectives, ranging from 4x to 40x, are used which allow all sections of the visual field to be simultaneously focused. The trinocular body permits the image to be either viewed with lOx wide-field eyepieces or sent to a video camera system. Also, the microscope body contains an analyzing polarizer that can be activated for observation of birefringence in the sample. 

PLAN or PL stands for planar and means the lens is corrected for curvature of field, and thus generates a flat field of image ... 

As mentioned, stellar spectra with right circular polarization obtained in the first exposure and left circular polarization in the second exposure are projeeted in turn on the same section of the CCD detector. Thus, errors in the flat-fielding procedure for two spectra with opposite eireular polarization are practically the same and do not affect the calculation of GMF in the ease of weak magnetic fields. Additionally, this observational technique automatieally allows us to rale out shifts of spectral lines caused by inaccurate adjustment of the CCD plane to the focal plane of the spectrograph and instrumental drift of contours of spectral lines during the second exposure relative to the first one. 

Fig. 3.2 I mage analysis procedure used for the images presented in this review, (a) The fluorescence images acquired at the adsorption (/ajs) and desorption (/jgs) potentials are divided by the image which represents the distribution of the incident intensity [1 ) creating flat field corrected images which are used for further analysis. The change in fluorescence is determined by...

Ability to remove other structural (fixed-noise) patterns by flat-field correction... 

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