LX7 awful edge resolution due to distortion correction

Started Apr 30, 2013 | Discussions thread
Samuel Dilworth
Samuel Dilworth Regular Member • Posts: 249
Distortion is the best compromise

Of the three latest LX-series cameras, the LX7 has the worst wide-angle distortion by far – necessary to squeeze such a fast and sharp lens into such a small package (barely bigger than the LX5, but twice as bright). The LX5 has the least distortion, and the LX3 is in between, though closer to the LX5 than the LX7.

Going to 24 mm-e in itself is not the problem. The problem is making such a lens both very fast and very small in size (and cheap too!). The Sony RX100 only goes to 28 mm-e, but because it’s fast and extremely miniaturised it has very similar distortion to the LX7 at 24 mm-e (and it’s soft in the corners even before distortion correction).

The important thing to note is that the LX7’s lens wouldn’t have sharper corners if it had been designed for lower distortion. On the contrary, allowing high distortion enabled better correction of other aberrations, with the final software-corrected image better than it would have been had distortion been made a higher priority – especially at large apertures.

However, since most aberrations improve on stopping down but distortion does not, if you stop down enough you’ll eventually get to the point where the lens with lower distortion delivers the sharper image even in the corners: the necessarily higher aberrations in the lower-distortion lens are insignificant at high f-numbers, allowing the lower distortion and lesser correction of distortion in software to win the day.

But at large apertures like f/2, it’s plain that the LX7 delivers a much sharper image in the corners than the LX5 (and both are better than the LX3).

All of the above refers to wide-angle performance. At longer focal lengths they’re all very similar.

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