Fluorite objectives

Salts are important in the processing of some natural materials and may be found as residues on or in objects. Fluorite, which is also called fluorospar, is commonly used for carvings, particularly in Asia. The translucent pastels of this material make it attractive, but its softness and perfect cleavage combine to make fluorite objects very fragile. 

Fluorite objective n. This objective is corrected both for spherical aberration and chromatic aberration at two wavelengths. 

A small but artistically interesting use of fluorspar is ia the productioa of vases, cups, and other ornamental objects popularly known as Blue John, after the Blue John Mine, Derbyshire, U.K. Optical quaUty fluorite, sometimes from natural crystals, but more often artificially grown, is important ia use as iafrared transmission wiadows and leases (70) and optical components of high energy laser systems (see Infrared and RAMAN spectroscopy Lasers) (71). 

Neofluar objectives are chromatically better corrected than the achromatic objectives (fluorite), but worse than the plan-apochromat objectives. The contrast of the neofluar objectives is however larger than with the plan-apochromat objectives. 

Fluorite is a ubiquitous mineral and is so widespread in ils occurrence that only the most noteworthy can be mentioned. The English localities at Cumberland. Durham, and Weardale are world famous. Exceptionally heauiiful handed material of hlue fibrous character fruin Derbyshire, known as Blue-John, has been much-used for decorative curved pieces, such as vases and other ornamental objects. Norway has produced exceptional specimens from the famous Kongshcrg silver veins, as well as yttrium-rich fluorite from northern Norway associated with rare-earth minerals. Fine material has been obtained from the Transvaal in the Republic of South Africa, Tasmania and Australia. Large quantities of fluorite are mined in Mexico at Guadalcazar and Guanajuato. 

The size and shape of ceria NCs are proven fo appreciably change the chemical and physical properties hence, their control in synthesis is one chief objective for study, and various nanoparticles, nanocubes, nanooc-tahedra, nanowires, and nanotubes have been obtained for this purpose. Owing to the cubic fluorite structure, ceria tends to form isometric particles, which present sphere-like morphology and are usually intermediates between the shape of cubes and octahedra. The major exposed crystal surfaces for ceria NCs are low index ones, that is, 100, llOj, and 111, with considerable surface relaxation and reconstructions. Figure 1 shows some typical morphologies of ceria NCs. 

Compensating eyepiece n. An overcorrected eyepiece designed to compensate for certain undercorrections in fluorite and apo-chromatic objectives. 

The objective lens is the most important part of the optical system. All lenses have information engraved on them, and it is helpful to be able to interpret this. An old lens may only show its focal length, but a typical modern lens may have Pol 25/0.55 0.17/170. The letters indicate the type of lens, here strain-free, suitable for use with polarized light. Different manufacturers may use different abbreviations, but most are readily understood. The most obscure is FI or Fluor this indicates a high quality general purpose lens, once (but no longer) made using the mineral fluorite. 

The ionic conductivity is a characteristic of materials rather sensitive to changes of the defect stmcture and to micro-ordering. The model of micro-ordering developed for description of fluorite-like solid solutions and the defect region model used for description of many objects explain equally discrepancy between the observed charge carriers concentration and the quantity of anion defects [43]. Besides of this, defect area volumes (3000-4000 A ) estimated from the B 2-x x 2+x conductivity data are very close to the associated supercluster size obtained by the micro-ordering areas model [43]. 

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