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Ealing / Beck 25-0506-000 15x Reflecting Objective - $750 (beavercreek)
Sunset Bluff near Fairfield
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This is a very nice example of one of the famous series of Beck / Ealing reflecting objectives. When properly adjusted, they are free of chromatic aberrations because all surfaces are reflecting - there are no refractive elements. The radii of the two reflecting surfaces are chosen in a way to correct for primary spherical aberration; primary coma, and primary astigmatism.
While they can be used as conventional microscopy objectives, they are of very large dimensions, and will not be parfocal with conventional refracting objectives. This particular objective, with a 15x magnification and a numerical aperture of 0.28, is over 51 mm long not including the mounting thread, and over 46 mm in diameter - too wide to mount other objectives in adjacent thread positions on most nosepieces
Unlike the higher magnification objectives in this series, the relatively low numerical aperture does not require the use of a correction collar for setting cover glass thickness. This objective has the standard aluminum coating, and the coating is in very fine condition on both primary and secondary. This objective does not include the cabinet and is missing the pair of Allen keys used to adjust the centration of the primary mirror, but they are of standard size and easily replaced. The instruction sheet for so doing is missing, as is a special target slide. The slide could be very easily replicated - it consists of a thin reflective substrate with a number of random circular voids that are used to adjust for coma. Centration can be accomplished in less than a minute.
Features of the objective include:
15x magnification 0.28 numerical aperture 1.30 mm visual field of view 24.5 mm working distance Standard RMS thread
will work in near UV with standard coatings, as well as into the IR.
These objectives were sold in the United States by the Ealing Catalog Company. The Ealing part number for this objective, with the standard coating, is 25-0506-000. Lens is in exceptional condition. It has the later type housing (not nickel-plated), and there are no blemishes in either mirror. This objective is currently supplied by Edmund Scientific in their 'TechSpec Adjustable ReflX' series