Light artifacts

As indicated above, stray light artifacts may have different causes as well as different appearances in the final image. Typically, the notion flare or lens flare is used as an umbrella term for all kinds of stray light artifacts. With respect to the manifestation and the characteristics of the effect in the image, a distinction is made between the following types of flare ... 

Fig. 15 Stray light artifacts by unsolicited luminous flux emerging from a glare source outside the...

Fig. 16 Suppressing the stray light artifact by using an appropriate lens hood...

It s time for a short recap concerning the different stray light artifacts that can occur... 

Deteriora.tlon. Apart from physical damage that can result from carelessness, abuse, and vandaUsm, the main problem with metal objects Hes in thek vulnerabihty to corrosion (see Corrosion and corrosion control) (127,128). The degree of corrosion depends on the nature and age of the object. Corrosion can range from a light tarnish, which may be aesthetically disfiguring on a poHshed silver or brass artifact, to total mineralization, a condition not uncommon for archaeological material. 

If a trace activity is indicated by the luminescence intensity measurement, the following two methods can be used to determine whether the light emission is due to the luciferase or it is an artifact (1) Measure the luminescence intensity with a buffer that contains 1 mM EDTA (add luciferase to this buffer and wait 1 min before mixing with luciferin). If the luminescence was caused totally by luciferase, the light intensity will be decreased to about 20% by EDTA (see Section 3.1.7). (2) Inactivate luciferase by acidifying the sample to pH about 2.0, followed by neutralization with NaHCC>3. Inactivated luciferase should not show any luciferase activity. 

Because carotenoids are light- and oxygen-sensitive, a closed-loop hyphenated technique such as the on-line coupling of high performance liquid chromatography (HPLC) together with nuclear magnetic resonance (NMR) spectroscopy can be used for the artifact-free structural determination of the different isomers. 

The relative instability of bromocriptine makes it very difficult to avoid artifact formation in test solutions or during spotting on the plate. Therefore, bromocriptine mesi-late, usually dissolved in chloroform/methanol 1 1, has to be spotted on the plate very rapidly and with the exclusion of light. The separation being terminated, the mobile phase is removed by means of high vacuum for 30 minutes. 

The emissive counterpart to CD is circularly polarized photoluminescence (CPPL). Where the fluorophore is chiral, then the photo-excited state can return to the ground state with emission of circularly polarized light, the direction of polarization of which depends on the relative intensities of the right-handed and left-handed emissions (/r and /L, respectively), which in turn depends on the chirality of the material, or more accurately, the chirality of the photo-excited state of the material. CPPL studies on poly silanes are extremely rare, however, due to the low CPPL intensity and rapid sample degradation in solution, and problems due to artifacts in the solid state. 

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