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alone. Elements may be cemented by oil or a soft cement in the case when the differential thermal expansion of crown and flint glasses causes hard or cured cements to warp or fracture. With larger elements, it is ideal to separate the lenses using a spacer. In a hard-cemented doublet, the lenses are
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was traditionally used for this purpose. Some doublets use no adhesive between the lenses, relying on external fixturing to hold them together, either because the optical design requires a gap or because
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Cementing elements can simplify raytracing operations as the cement may nearly always be ignored, with the tracer treating the ray as if it refracts directly from one element into the next.
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paired together. Such an arrangement allows more optical surfaces, thicknesses, and formulations, especially as the space between lenses may be considered an "element". With additional
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differences between the two lenses will not allow cementing. These are called "un-cemented", "air-spaced" or "broken contact" doublets. A sub-type of air-spaced doublet is the
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Cementing elements requires a high precision to ensure correct centering of the cemented components. This difficulty greatly increases on groups of more than two elements.
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A guide to instrument design – Scientific
Instrument Manufacturers' Association of Great Britain, British Scientific Instrument Research Association, page 184
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Provides superior control for minimising spherochromatism and other aberrations, allowing the creation of more advanced optical systems using fewer elements.
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Precision cementing is high in manufacturing cost. It is often cheaper to AR-coat two air-spaced elements.
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Clarkson, E. N. K.; Levi-Setti, R. L. (1975), "Trilobite eyes and the optics of
Descartes and Huygens",
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Doublets can be air-spaced, cemented, or "oiled". Oiled doublets hold the optical fluid in place with
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lens that is difficult to mount with an equivalent doublet made from two higher-power lenses.
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Cemented groups may assist to decrease the physical length of the optical system.
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with four elements, comprising two doublets. The front doublet is air-gapped and
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To prevent total reflection at the air-film interface due to critical ray angle.
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There are several advantages and disadvantages to cementing elements together:
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To eliminate the reflection losses of two air-glass surface interfaces.
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Doublets can come in many forms, though most commercial doublets are
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Fred A. Carson, Basic optics and optical instruments, page AJ-4
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Fred A. Carson, Basic optics and optical instruments, page 4-32
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Lenses may be cemented together for any of several reasons:
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with mechanical strength, such as optically transparent
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226:. Often one element is a positive lens made of
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407:Kingslake, R. (2010). Johnson, R. B. (ed.).
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230:and the other is a negative lens made of
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411:(2nd ed.). SPIE Press. p. 5.
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160:chromatic aberrations
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250:held together by an
212:spherical aberration
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208:chromatic aberration
47:improve this article
16:For other uses, see
376:1975Natur.254..663C
216:optical aberrations
192:optical aberrations
62:"Doublet" lens
220:refractive indices
194:more thoroughly.
188:degrees of freedom
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103:December 2009
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45:Please help
40:verification
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240:Apochromats
232:flint glass
228:crown glass
164:astigmatism
148:camera lens
531:2 (number)
520:Categories
347:References
301:Advantages
236:Trilobites
224:dispersion
214:and other
142:Carl Zeiss
73:newspapers
204:achromats
156:spherical
152:divergent
330:See also
252:adhesive
392:1091864
372:Bibcode
269:dialyte
176:doublet
140:An old
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526:Lenses
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363:Nature
275:Cement
172:optics
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