  We construct an electron optical system to investigate Bragg diffraction (the
crystal lattice plane, $10^{-2}$-$10^{-3}$ rad) with the objective lens turned
off by adjusting the current in the intermediate lenses. A crossover was
located on the selected-area aperture plane. Thus, the dark-field imaging can
be performed by using a selected-area aperture to select Bragg diffraction
spots. The camera length can be controlled in the range of 0.8 to 4 m without
exciting the objective lens. Furthermore, we can observe the magnetic-field
dependence of electron diffraction using the objective lens under weak
excitation conditions. The diffraction mode for Bragg diffraction can be easily
switched to a small-angle electron diffraction mode having a camera length of
more than 100 m. We propose this experimental method to acquire electron
diffraction patterns that depict an extensive angular range from 10$^{-2}$ to
10$^{-7}$ rad. This method is applied to analyze the magnetic microstructures
in three distinct magnetic materials, i.e., a uniaxial magnetic structure of
BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$, a martensite of a Ni-Mn-Ga alloy,
and a helical magnetic structure of
Ba$_{0.5}$Sr$_{1.5}$Zn$_{2}$Fe$_{12}$O$_{22}$.
