>The angle of deflection (theta) is:
theta = (4GM)/(cr^2)
toward the mass M at a distance r from the affected radiation, where G is the universal constant of gravitation and c is the speed of light in vacuum.[0]
The best resolution our eyes can offer is about one arcminute (1/21600 of a turn). Depending on your distance from the object, just plug in some numbers.
Say at the earth-moon distance 384400 km the object must be about 24x the mass of the sun to bend the incoming light at one arcminute (~0,0002909rad).
The sun actually bends light at about 2 arcseconds as seen from Earth; the focal point would be about 542x the distance Sun-Earth. [1]
Alternatively the object of say 1m^3 volume at a distance of 10 meters will bend light by 1 arcminute if it weighs 3.27x10^16 kg, the density of about 1/10th of a neutron star.
To conclude: one will be instantly overwhelmed by the gravitational forces before being able to see an object bend light with one own eyes. That's why this kind of extreme bending/lending is reserved for galaxy clusters.
[0]https://en.wikipedia.org/wiki/Gravitational_lens#Explanation...