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Analysis of strong gravitational lensing depends on software analysis ofobservational data. The purpose of this study was to evaluate the behavior ofstrong gravitational lens modeling software with changes in redshift. Fourdifferent strong gravitational lens software modeling codes were directlycompared (Lenstool / glafic, two light traces mass codes, and GRALE / PixeLens,two non-light traces mass codes) in the analysis of model data as well asanalysis of the giant gravitational quasar SDSSJ1004+4112. A generalized modelfor time delay calculation shows that calculated time delay is proportional to$D_{d}D_{s}/D_{ds}$.The percent change in time delays calculated for eachsystem at each redshift tested were compared with percent change in the valueof $D_{d}D_{s}/D_{ds}$. A simple point mass model was tested with each code.Five models were used with a constant $z_{lens}$ and a varying $z_{source}$,and five models with a constant $z_{source}$ and a varying $z_{lens}$. Theeffects of changing geometry were similarly investigated for SDSSJ1004+4112. Ingeneral, the changes in time delay were of a similar magnitude and directionalthough, some calculated time delays varied by as much as 30 percent fromchanges in $D_{d}D_{s}/D_{ds}$. Changes in calculated mass for the point massmodel with a constant $z_{source}$ were almost identical to changes in$D_{d}D_{s}/D_{ds}$ for three of the four codes tested. These data demonstratethe effect of changes in redshift on parameters calculated by each of the codesas compared to changes in $D_{d}D_{s}/D_{ds}$. The paucity of existing directcomparison studies of strong gravitational lensing supports the need for morestudies of this kind. These results show that even small changes in redshiftaffects the calculation of time delay and mass, and that the effect on thecalculations is dependent on the particular software used.

Comparison of Strong Gravitational Lens Model Software I. Time delay and  mass calculations are sensitive to changes in redshift and are model  dependent