The amplification of the protogalaxy candidate cB58 due to gravitational lensing by the foreground cluster of galaxies MS1512.4+3647 is quantified based on recent ROSAT and ASCA X-ray observations .
It is found that the amplification is at most 25 for any reasonable cosmological model with or without cosmological constant .
It is also argued that the system may be used to place new constraints on the value of the cosmological constant .
The gas mass fraction for this cluster is found to be about 0.2 .