bad_doggie
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petrescu wrote:
Pitfalls: Comparing apples to oranges. MTF of a 55mm compared to a 50mm, and 1.6x image circle compared to ff, f/2.8 compared to a f/1.2. Expecting an excellent 50/1.2 to stick on the ceiling (it'll never happen, if you want that check the 300 at f/8).
yes and no. i *did* warn about these things. and it was all part of an off topic tangent in this thread.
nevertheless, 60mm and 55mm and 50mm are not really apples and oranges FLs: these are the lenses i already have at this FL, and 5-10mm is not a huge difference at this FL. (and you can add to that, the 5/1.4.) and for me, i *do* have an aps-c camera: the only relevant portion of the mtf chart is the first 3/5 of it.
if i'm gonna buy a 50/1.2, when will i use it? apparently, from comparing those charts, i'm ONLY going to pull it out when i need f/1.2 - f/2.8, unless its sweet spot is around f/4-f5.6 and its REALLY sweet and that's not obvious from the charts.
the 50/1.4 is a pretty sharp lens from f/2 or f/2.2. so that means that the real question is: will it be exceptional at f/1.2-f/2? we'll have to see. but that's really the only use for this lens, for me. the performance (again, based only on the charts) doesn't scream "optical miracle" at f/1.2. it says something more like "i'm kinda like the 50/1.4 wide open". which kinda sucks. so i'm not too excited yet.
and, of course, the whole point of the 17-55 @ 55 example above was to say: when you see a chart like this, you say, "wow, i want this lens". almost without trying it. well, i do, anyway. others here seem to be saying things like that about the 50/1.2 anyway, but i think largely because of the "L" and the aperture. but we also know that previous really fast 50mm lenses have often not lived up to expectations.
Avoid the following pitfalls: (1) don't compare apples to oranges and (2) don't compare oranges to apples.
The only _approximatively_ meaningful MTF comparisons that could be done are: the 50/1.4 at f/8, FD 50/1.2 at 1.2 and Leica 50/2.8 at f/8 and only 10lpmm.
That's the only thing one could do with the published MTFs of Canon, Leica and Zeiss.
"approximatively"?
ah yes, well, the comparison between 50 and 55 and 60 is my prerogative, since i'm a consumer and not an engineer. that's a *practical* comparison. the charts themselves, alas, are the only ones that canon makes available. but we can make some reasonable assumptions - e.g. that the performance improves continuouosly from wide-open to f/8 (suggesting that the 50/1.2 is not gonna beat my 60/2.8 at 2.8). or for the 17-55, that it has similar performance at 50 to its performance at 55 (heck, it should be better, no? it *is* a zoom after all.)
anyway, we're presented with skeletal info in mtf charts. even more so with zooms. we're invited to interpolate the additional data. if canon or others want to highlight some aspect of the performance that can't be inferred from the charts, they're of course free to publish 3d charts, across all apertures as well. but they don't because they don't have to ...
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