While Kolari mod is great solution for wide-angle rangefinder lens users,
personally I still hesitate to modify my A7 because such unofficial mod voids warranty.
Today I would like to introduce another solution to fix corner smearing issue.
I believe Astigmatism is the principal cause of corner smearing.
I tried some optical simulations and found that a plano-convex lens placed in front of the WA RF lens can control astigmatism.
I use OSLO free edition: http://www.lambdares.com/oslo-university-program
For simplicity, simulation use perfect lens instead of complicated actual lens design.
I think symmetrical lens design such as Biogon matches this simplified simulation, but retrofocus design does not.
Here are the results.
Astigmatism at Extreme Corner:
21mm lens with 1.8mm thick cover glass (Original A7): 0.6mm.
21mm lens with 0.8mm thick cover glass (Kolari/Leica): 0.25mm.
1.5m plano-convex in front of 21mm with 1.8mm cover glass: 0.14mm.
28mm lens with 1.8mm thick cover glass (Original A7): 0.4mm.
28mm lens with 0.8mm thick cover glass (Kolari/Leica): 0.18mm.
2m plano-convex in front of 28mm with 1.8mm cover glass: 0.07mm.
So theoretically, plano-convex method outperforms Kolari/Leica in terms of astigmatism!
Oct 03, 2016 at 06:20 AM
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