Lens review
2007-09-21
Sigma 50-150mm f/2.8 APO EX DC HSM
7. Coma and astigmatism
Coma is corrected almost perfectly. Again performance in this category is similar to Sigma 70-200 f/2.8. In both cases image of the diode is almost ideally round in the center and at the borders. Well done!
Astigmatism correction is good only for 50 mm. No wonder image resolution at border was so excellent. For this focal length average difference between horizontal and vertical values of MTF50 function is only 3%.
It is much worse for longer focal lengths. We can see that beside chromatic aberrations astigmatism is the main reason of worse image resolution at borders. For 100 mm it is equal to 12% and for 150 mm goes even higher to 14%.
