The purpose - to make sure the lens could be used hand held in reasonable lightning conditions.
Samples presented: RAW files converted in Lightroom with default settings, full size crop + exposure correction.
Conclusion: This lens deserves "A" for excellent sharpness, contrast and reasonable auto focus speed. For the purpose of animal/birds photography, absence of image stabilization is not important as shutter speeds must be high anyway to avoid motion blur of the subjects.