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 p.11 #11 · A thinner sensor stack may be possible after all! | |
uhoh7 wrote:
I must concur about the extreme corners of the biogon on the M9 at infinity, which was quite a shock to me. I spent quite a few hours trying to decide where to go at 35mm on the M9, considering every f/2 option. I choose the biogon simply because it seemed to offer the best technical reproduction and also good performance at f/11.
I have to wonder, would the latest 35 cron asph give better fidelity in the deep corners on M9?
I can only go by MTF comparison at wider apertures (Zeiss only shows up to f/4 and Leica f/5.6), but my feeling is there is some tradeoff. The Cron, like a lot of Leica lenses, has a wavy higher lp/mm curve that indicates recovery towards the image edges, but likely giving up something in the mid zone area, until well stopped down. The ZM curves at f/4, both for the 35/2 and the new 35/1.4, show more level, even, performance across most of the frame, before dropping off at around 17-18mm from center. Of the two ZMs, the Biogon improves gradually over the mid zone from just under 70% (40lp/mm) to just over 80%, before tapering off towards the edges. The new Distagon seems to be more Leica-like, starting off strongest centrally at just over 80%, holding it level the first 5-6mm, dipping a bit in the middle from 7-16mm, though not nearly as dramatically as the Leica, always staying at or above ~65%, recovering at 16-17mm, then dropping off from 80% (sagittal) to 60% at 20mm and 50% by the corner. The Biogon drops from 60 to 40 (sagittal) past 19mm. Both ZM MTFs show that sagittal and tangential lines remain relatively close together. With the Cron ASPH, there is considerable divergence past 17mm, where sagittal increases from 60% and peaks at almost 80% (40lp/mm) at 20mm, while tangential plummets from 60% at 17mm to a bit under 20% at the corner. My guess is the Cron holds better corner detail than the Biogon in one direction, but gives up considerably in the other, which may look somewhat unsettled. In your example, the extreme corners of the Biogon just go kind of softish, but don't really call attention to the problem. There's also the question of how the thin Leica cover glass affects performance and whether this is included in any of the MTF measurements. Back a while ago theSuede commented that the cover glass quality used for the M9's sensor was relatively poor (this was well before the corrosion problem was acknowledged) and might degrade peripheral lens performance, which apparently has been improved with the M240's sensor...
TLDR: The Biogon and new Distagon are probably the best 'fast' 35mm RF options for holding edge/corner detail, though variables in sensor toppings will play a role here as well. Not mentioned above is the Lux ASPH FLE... also has wavy MTF character, but at the corners seems much better at f/5.6 than the Cron ASPH: sagittal in the 70% range, tangential at about 50%. I guess the Cron's design is somewhat of a compromise between size and performance while the ZMs trade compactness for more gradual, consistent performance.
BTW, the ZM35/2.8 seems to be somewhere between the two other ZMs... It's MTF character more closely follows that of the Distagon, but generally tracks 5-10% lower across the frame at f/5.6 (40lp/mm), while the Distagon's measurements are at f/4...
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