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f is the combination focal length, if conjugate distances s and s ″ are measured from the combination principal points. Theseremarks apply, in particular, to our two-element air-spaced con- densers. To facilitate use of the simple lens formula, we have tabu-lated condenser effective focal lengths f

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Two-Element Air-Spaced Condenser Lenses - 12567 Two-ElementAir-Spaced Condensers

Multielement Lenses Cylindrical Optics Condensers are used to project or display an image of an illu-minated object. Examples include film and slide projectors, inte- grated circuit mask projectors, optical comparators, profile gauges,and similar equipment. A condenser has two primary duties in pro-jection systems. It must first transfer radiant energy efficiently from a light source to the entrance pupil of a projection lens system, sothat the brightness of the projected image is maximized. Second, itmust provide highly uniform illumination of the object plane or film gate (the location of a slide, motion picture, or microfilm frame)to be projected.Melles Griot two-element air-spaced condensers are designedto do both of these tasks efficiently over a large range of conjugateratios and at a low f-number. They are available in two materials and are well suited for applications requiring efficiency and uniformity.Efficient radiant energy transfer from a source into the projec-tion lens system is accomplished by using a condenser close to the source, with minimum spherical aberration at the resultant large con-jugate ratio. Low f-number operation is also obviously advanta-geous. Spherical aberration, which at low f-numbers can cause significant energy loss, has been minimized in Melles Griot con-densers by a two-element air-spaced design. The f-number for allcondensers is 1.0.Uniform film-gate illumination is achieved by placing the gateclose to the condenser’s secondary principal plane. Irradiance dis- tributions at the condenser principal planes are essentially identi-cal. If an ideal point source is used, irradiance distribution at thecondenser’s primary principal plane would be nonuniform by inverse square law approximation. The finite size of real sourcesconsiderably improves uniformity of distribution at the primaryprincipal plane of the condenser. Clearly there is a trade-off between uniform film-gate illumination and the proximity of the condenser to the source (large conjugate ratio). Melles Griot condensers havebeen designed to be short, allowing close approach to condenserprincipal planes. If necessary, a flat hot mirror and/or heat-absorb- ing glass filter can be placed between the condenser and the film gate.Film, filter (if any), and condenser can all be forced-air cooled. Thecondenser housing has six vent holes to enhance cooling. Lenses can be easily removed from the housing for cleaning. When designing projection and illumination systems, it is espe-cially helpful to locate the conjugate points of a condenser. Thesimple lens formula is where 111 +′′= ssf
Mirrors 1 and positions of thecondenser (combination) principal points H
1 and H
1 ″ . These posi-tions are referenced to the external lens vertices and mount. SELECTING THE PROPER CONDENSER Frequent reference will be made to the figure on page 7.33. Weassume that you have a specific projection task in mind, and havealready determined values for the following quantities:from known film and desired image size;
Prisms andRetroreflectors mss ′
222 =′ f
2 , the projection lenssystem’s effective focal length and, CA
2 , the clear aperture of pro-jection lens system, given by
Beamsplitters, Windows, Optical Flats f
2 divided by f-number.The conjugate distance s
2 , from film gate position to projectionlens system primary principal plane, is given bySpecifically allowing room for an optional heat-absorbing filter,we may now set sfm
222 =+  11  .  
Polarization Components shhrb.
121 ′′=+

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7.31