08-31-2010, 09:31 PM
[quote name='popo' timestamp='1283283371' post='2384']
Samples at [url="http://asia.olympus-imaging.com/products/dslr/mlenses/75-300_48-67/"]Olympus Asia[/url]. Doesn't look so good to me.
The Olympus MTF is at 20 and 60 lines/mm... how do you compare that to Canon for example, who use 10 and 30 lines/mm? Is there a line pairs doubling I'm overlooking? Or are they really testing at a higher frequency?
[/quote]
Not sure. I am used to the spatial frequency being quoted in line pairs per mm (lpmm). Since both give lines per mm, there might be a factor of 2 hidden or this is just some sloppiness involved here. Since the Olympus lenses are meant to cover a smaller sensor with crop factor 2, quoting twice the common values would make sense from a technical point of view. From a marketing point of view, 10 and 30 like most companies would look better.
Comparing MFT numbers measured by different people is impossible. They don't give you enough details. Things like, are these computed or measured MTF. Do they use white, coloured or even monochromatic light? White light typically gives lower values.
I agree, with you on the samples. They are full of artefacts - most likely to high JPEG compression.
Samples at [url="http://asia.olympus-imaging.com/products/dslr/mlenses/75-300_48-67/"]Olympus Asia[/url]. Doesn't look so good to me.
The Olympus MTF is at 20 and 60 lines/mm... how do you compare that to Canon for example, who use 10 and 30 lines/mm? Is there a line pairs doubling I'm overlooking? Or are they really testing at a higher frequency?
[/quote]
Not sure. I am used to the spatial frequency being quoted in line pairs per mm (lpmm). Since both give lines per mm, there might be a factor of 2 hidden or this is just some sloppiness involved here. Since the Olympus lenses are meant to cover a smaller sensor with crop factor 2, quoting twice the common values would make sense from a technical point of view. From a marketing point of view, 10 and 30 like most companies would look better.
Comparing MFT numbers measured by different people is impossible. They don't give you enough details. Things like, are these computed or measured MTF. Do they use white, coloured or even monochromatic light? White light typically gives lower values.
I agree, with you on the samples. They are full of artefacts - most likely to high JPEG compression.
enjoy