replacing film with a similar-sized digital sensor is possible, but expensive because larger sensor areas imply a greater probability that a defect will render the sensor non-functional. such "full frame" sensor digital slrs (dslrs) however gained early popularity with professional photographers who could both justify their initial high cost, and retain the use of their investment in expensive 35 mm film lenses. by 2008, full-frame models such the canon eos 1ds and 5d, the nikon d3 and d700, and the sony alpha a850 and alpha a900, designed and priced for professionals, were available.