Recent physics loves mathematical models. Question is not, if it is absolutely right; question is, if tool recently loved is applicable to seeing something, what is by present physics suppressed.
Present physics suppresses, that experiments and observations often have alternative explanations. For example gravity lens have explanation using law of optics. Name with gravity is skillful trick, how optics to cut out. Phenomenon, led to optics, is interplanetary gas-dust; see Zdenek Kopal. Other option is Maxwell field; accept possibility case of field is similar to case of matter.
Make (mat) models for 2 explanations Gravity Lenses. Very detailed model will show difference between both possibilities. Gravity is maximal for little distance.
fi = G m c^-2 r^-1
Fi .. deflexion, G gravity constant, m mass, r radius
About effect of gas or field, effect for little distance is minimal, on the contrary.
fi = v/c * (r/r0)^2 /(1+(r/r0)^2)
Compare with common lens
fi = v/c * (r/r0) , r < r0
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Effect of gas or field has non-linearity, but this non-linearity is many times less than in case of gravity lens. Effect of gravity has optical error larger and in full range of distance.
http://en.wikipedia.org/wiki/Gravitational_lensing Einstein rings, arcs, and multiple images, their distortion of picture is kind of optic error in maximal radius of lens. This distortion has gas and field also. But gravity has great distortion for minimal radius; only it is parameter really relevant for comparison both possibilities.
If somewhere is Einstein ring (, and gravity explanation is right), than in distance n-times smaller is curvature n-times greater. Precise PC iterative model of presented phenomenon have to show some set of pictures; we can it compare with our observation of cosmos.