Hmm .. cool... interesting ... as an aside, (but still related to lensing calcs) ..
I found this one (albeit, another journo's article), dated Jan 2010 but the quality seems to be OK ...I'll try finding the scientists paper, when I get a chance.
Weak Lensing Gains Strength
http://www.physorg.com/news183144919.html
It contains some good words explaining how they're using X-Ray data to calculate where the centre of the lens is, for weak lensed objects, thereby improving the mass calculations...
"Berkeley Lab cosmologists were part of an international team that has extended the relationship between the x-ray luminosity and the mass of galaxy clusters as measured by gravitational lensing, improving the reliability of mass measurements of much older, more distant, and smaller galactic structures. These refined measurements will benefit both the understanding of dark matter and the nature of dark energy as well."
....
“By confirming the mass-luminosity relation and extending it to high redshifts,” Leauthaud says, “we have taken a small step in the right direction toward using weak lensing as a powerful tool to measure the evolution of structure.”
The article gives more details on how they go about these calculations ... (Note: these calcs only apply to weak lensed objects .. not in the same class of Abell 1689 . which is a massive object).
Interesting.
Cheers
PS: 'Lensing' seems to have taken off over the last couple of years or so, with different classification types, methods, etc and seems to be the primary tool being used in the hunt for darkness. Lots more to learn, in order to understand the outcomes ! Rgds.