Originally posted by DSLRnovice Thanks for posting these. From what I can tell, the difference between the FA20 and the M20 is not as significant as I would have expected from the various comments in the forum. If there are quality differences that are not reflected as much in this test but might be important, have you noticed any?
The FA20 optical design seeks to limit CA/ purple fringing. The extreme corner crop shows this well (compared to the M 20mm and FA 20-35mm). I have found correcting the CA/ PF in the M 20 and FA 20-35 to be a little difficult.
For the above reason it seems that the FA 20 delivers better colour rendition across the whole frame.
However, this comes at a cost. The FA20 appears to suffer from some distortion greater than the M 20mm and FA 20-35mm. Barrel and pincushion distortion is evident.
Overall, the FA 20 is substantially sharper in the middle with almost no CA/PF. Colour rendition is better too.
Why choose f2.8 over f4? While shooting at f2.8 has a clear downside in the corners (nasty) it does give you capacity for DOF creativity if you intend to crop out the upper and lower portion of the frame (i.e. crop to 16:9 ratio). It also gives you the same flexibility in low light if the landscape scene you are capturing is best represented in that ratio.
If you want the M20mm then you are probably paying about US$350-400. For an extra US$100 you get greater performance at f8 and more flexibility wide open knowing the limitations in the corners. Also, the aperture setting can be changed within the camera. Flare control has not been tested, but, I suspect the coatings on the FA20 to be better in this department.
For an investment of that amount I would upgrade to the FA20 without hesitation.