We present a long-working-distance objective lens with numerical apertures NA = 0.4 for single-atom experiments. The objective lens is assembled entirely by the commercial on-catalog Φ1″ singlets. The objective can correct the spherical aberrations due to the standard flat vacuum glass windows with various thicknesses. The typical working distance is 18.2 mm at the design wavelength of 852 nm with a 5-mm thick silica window. In addition, the objective can also be optimized to work at the diffraction limit at a single wavelength in the entire visible and near infrared regions by slightly tuning the distance between the first two lenses. The diffraction limited field of view is 0.61 mm, and the spatial resolution is 1.3 μm at the design wavelength. The performances are simulated by using the commercial ray-tracing software and confirmed by imaging the resolution chart and a 1.18 μm pinhole. The objective can be used for trapping and manipulating single atoms of various species.