The evidences on gravitational lensing are fairly standard and direct.
About Gravitational Lensing:
In the case of a gravitational lens, the deflection decreases with increasing distance from the central axis. In fact, for a point-like gravitational lens of mass M , if b represents the impact parameter of a light ray (the perpendicular distance from the initial path of the ray to the lensing body), then the angle of deflection θ is given by
θ = 4GM/c2b ,
and the distance D from the lens to the point at which the light crosses the axis is given by
D ≈ b/θ = c2b2/4GM
About Gravitational Waves:
The evidence on gravitational wave is indirect. After the following discourse it will be difficult to argue the sustainability of some of the hypotheses regarding Gravitational Waves.
Assume a super-massive black hole (occurring commonly at the centre of galaxies, formed with the galaxies themselves) in isolation. It is a common candidate to emit gravitational waves [by itself. in contrast to common belief that violent anisotropic events, such as matters falling into black holes, super-heavy masses rotating about a common centre of mass, supernova explosion, etc., can only produce gravitational waves]. A Black Hole almost always has an intrinsic anomaly, such as rotation, precession, nutation, other fluctuations, such as vibration along its radius, etc., for which it can emit gravitational waves.
Let us assume that with a uniform star-field in the background along our line of sight, a super-massive spherical object, placed in between our eyes (or photographic plates/CCD camera, etc.) appears as a circular disk, and has on the periphery of the circular disc, gravity waves emanating from the object.
Since the object is in a steady state, the steady state gravitational waves are to produce stationary regions of wave maxima and minima (analogous to the ripples created by throwing a stone into a water body). These regions of periodic gravitational wave -maxima and -minima are therefore in the form of annular rings of diffraction gratings of decreasing strength from the centre of the super-massive object for light waves originating from the background star(s) directly along the line of sight.
The light from the star-field along the line of sight from the star-field and super-massive object will therefore be diffracted by the annular rings of the gravity waves and therefore produce in our field of view regions of maxima and minima. Since the light is comprised of the full region of the electromagnetic spectrum, the constituent wavelengths will form a fraunhauffer Interference pattern [View Link] detectable by photographic plate, CCD camera, etc.
Now, if the object is in a quasi-steady state the interference pattern will keep changing over time. In the case of non-stationary state, the Fraunhoffer Interference pattern will keep varying over time very quickly, but there will be a pattern nonetheless.
Such an observation (or absence) of steady-state to rapidly-varying multi-frequencied Fraunhoffer interference pattern spanning the entire E.M. Spectrum will either prove or disprove directly, the phenomenon of gravitational waves.
(1) Pages 306-338, Relativity: SPECIAL, GENERAL, AND COSMOLOGICAL, 2nd Ed., by Wolfgang Rindler, Professor of Physics, The University of Texas at Dallas
(2) Pages 77-79, Gravity, Black Holes, and the Very Early Universe: An Introduction to General Relativity and Cosmology by Tai L. Chow, California State University Stanislaus, Turlock, CA, USA
(3) An Introduction To Modern Cosmology, Second Edition, Andrew Liddie, Univ. of Sussex, U.K.
(4) Pages 226-232, Art.7.4.2, Methods of detecting gravitational waves, Robert J.A.Lambourne, Relativity, gravitation and cosmology
(5) Pages 280 to 321, GRAVITATION AND COSMOLOGY: PRINCIPLES AND APPLICATIONS OF THE GENERAL THEORY OF RELATIVITY, STEVEN WEINBERG, Massachusetts Institute of Technology
(6) 1979, Dennis Walsh (1933–2005) and his colleagues pointed out that two narrowly separated quasars, Q0957+561 A and B, have identical optical and radio spectra.
(7) Abell 2218, a rich cluster of galaxies located
about 2 billion light-years away, enables a far more distant object to be detected
(8) Quote from (4) mentioned above “… In 1993 the Nobel Prize for Physics was awarded to Joseph Taylor (1941– ) and his former graduate student Russell Hulse (1950– ) for their discovery (in 1974) and subsequent study of a very unusual binary star system that has become a test-bed for general relativity. The Hulse–Taylor system is believed to consist of two neutron stars, one of which is emitting regular pulses of radiation at radio wavelengths and is therefore classified as a pulsar and designated PSR B1913+16. Pulsars were first detected in the 1960s by Jocelyn Bell Burnell (1943– ) and it was soon proposed that they were actually rapidly rotating neutron stars with a strong magnetic field. Many are now known but PSR B1913+16 was the first binary pulsar — a pulsar confirmed as part of a close binary system. In the Hulse–Taylor system, both of the compact stars has a mass of about 1.4 M, and the pair orbit each other with a period of just 7.75 hours. The star that is a pulsar is thought to turn on its axis 17 times per second, accounting for the observed pulse separation of 59 milliseconds.
“According to general relativity, a system of this kind should mainly lose energy through the emission of gravitational waves, a form of radiation involving propagating distortions of spacetime that was proposed by Einstein in 1916. As a result of gravitational wave emission, the orbital period of PSR B1913+16 should be decreasing in a predictable way. This prediction has now been tested over more than three decades and has been found to accurately agree with observations to within 0.2% (see Figure 7.19). It is an impressive confirmation of general relativity and also an indirect confirmation of the existence of gravitational waves, which have still not been directly detected here on Earth…”