Patent Number: 
Section: claims

1. A method of three-dimensional image reconstruction for reconstructing a three-dimensional image of a specimen based on TEM (transmission electron microscope) images by tilting the specimen at plural tilt angles and obtaining the TEM images at these tilt angles, wherein(a) a positive focal point position of an objective lens incorporated in a transmission electron microscope is detected at each of the tilt angles of the specimen,(b) a focal point position of the objective lens is set to plural positions which are shifted from said positive focal point position by amounts of defocus Δf1, . . . , Δfn, respectively, at each of the tilt angles of the specimen and a TEM image is obtained at each of the set focal point positions,(c) a single optimum TEM image is selected at each of the tilt angles of the specimen from the TEM images obtained by the steps (a) and (b) above, and(d) a three-dimensional image of the specimen is reconstructed based on the selected TEM images. 2. A method of three-dimensional image reconstruction as set forth in claim 1, wherein said amount of defocus Δf1 is previously found by performing the steps of:setting the tilt angle of the specimen to an arbitrary angle θ1;detecting the positive focal point position f, of the objective lens at the set tilt angle θ1 of the specimen; andvarying an excitation current flowing through the objective lens such that an optimum TEM image is obtained and finding the amount of defocus Δf1 from the difference between the focal point position of the objective lens occurring at this time and said positive focal point position f1,wherein amounts of defocus other than Δf1 are previously found in the same way as Δf1. 3. A transmission electron microscope for reconstructing a three-dimensional image of a specimen by tilting the specimen at plural tilt angles, obtaining a TEM image at each of the tilt angles, and reconstructing the three-dimensional image based on the obtained TEM images, said transmission electron microscope comprising:defocus amount storage means for storing plural amounts of defocus Δf1, . . . , Δfn;positive focal point position detection means for detecting a positive focal point position of an objective lens at each of said tilt angles of the specimen;focal point position-setting means for setting a focal point position of the objective lens to positions shifted from the positive focal point position detected by said positive focal point position detection means by said amounts of defocus Δf1, . . . , Δfn, at each of said tilt angles of the specimen;an image memory for storing TEM images obtained at the focal points set by said focal point position-setting means in a corresponding manner to the respective tilt angles of the specimens;display means for displaying the TEM images stored in the image memory;image selection means for selecting one TEM image from the TEM images displayed on the display means at each of the tilt angles of the specimen; andthree-dimensional image reconstruction means for reconstructing a three-dimensional image of the specimen based on the TEM images selected by said image selection means.