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Unformatted text preview: Biological Microscope Components Biological microscopes are specially desgined to view primarily ﬂuid-like speci-
mens that are held between a microscope slide (on the bottom) and a thin cover glass
(on the top). The cover glass is usually 0.17 mm or 0.18 mm thick. The specimen is il-
luminated from below so that the light propagates through the microscope slide, then
through the specimen, and then through the cover glass. Due to the large angles of the
rays with respect to the axis of the optical system, the cover glass slab introduces spheri-
cal aberration into the imaging process. To compensate for this, biological objectives are
designed and fabricated that largely cancel this cover—glass—induced aberration. A biological microscope has an objective with engraved markings on it as follows:
“Achro” and “40 / 0.65” and “160 / 0.17.” “Achro” indicates that it is an achromatic
(color corrected) objective. The “40” means that it is a 40X linear magniﬁcation ob-
jective. The “0.65” is the numerical aperture of the objective. The “160” refers to the
length in mm of the microscope tube with which it is designed to be used and the “0.17”
indicates the thickness in mm of the cover glass for which the objective is corrected.
This microscope has an eyepice with engraved markings on it as follows: “WF10X.” The
“WF” means that it is a Wide Field type of design and the “10X” is the angular mag-
niﬁcation of the eyepiece. The ﬁeld stop in the eyepiece is 10.35 mm in diameter. The
outside of the eyepiece tube is a standard 23.2mm diameter. Calculate, showing all work, the focal length of the objective. Express your an-
swer in mm accurately to three signiﬁcant ﬁgures. Calculate, showing all work, the focal
length of the eyepiece. Express your answer in mm accurately to three signiﬁcant ﬁg-
ures. Calculate, showing all work, the diameter of the magniﬁed area that is seen when
viewing through the microscope. Express your answer in um accurately to three signiﬁ-
cant ﬁgures. Put your answers in the spaces provided below. Focal length of objective = mm
Focal length of eyepiece = mm Diameter of area seen through the microscope = pm Biological Microscope Components Mk L_*' From similar triangles Then the linear magniﬁcation of the objective is I L
m=— —=40.0 0 _ f0
Since L = 160 mm, then f0 = 4.0 mm. The eyepiece adjusted for inﬁnity focus has anglular magniﬁcation M = 250mm = 10.0
f6 2 25mm The ﬁeld stop has d = 10.35 mm and it located at the image plance of the objective.
The diameter of the ﬁeld viewed is D = i = 258.8,um
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This note was uploaded on 04/29/2008 for the course ECE 4500 taught by Professor Gaylord during the Spring '08 term at Georgia Institute of Technology.
- Spring '08