Let's talk about cross-format comparisons with MTF-50 tests.

Started Jun 27, 2012 | Discussions thread
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Great Bustard Forum Pro • Posts: 38,980
Let's talk about cross-format comparisons with MTF-50 tests.

Let's start with:


Please note that the tests results are not comparable across the different systems! This does also apply for the new EOS tests based on the EOS 50D because of differences in the sensor system (e.g. AA-filter) as well as different RAW-converters.

This makes sense, of course, if we are talking about the lens, and not the system. But if we are talking about the system, then why would a review site convert RAW files in such a way that the MTF-50 scores would be so radically different than if they used a different RAW converter?

An MTF-50 test measures the resolution at 50% contrast. We know that sharpening affects contrast, therefore, sharpening will affect the MTF-50 score. But, if the same sharpening is applied to each file, what effect will that have?

That is, let's say the unsharpened file results in MTF-50 scores of 800 lw/ph and 1200 lw/ph -- 50% greater resolution at 50% contrast for the second system. We apply the same sharpening to both systems (what does "same sharpening" even mean?). What effect will that have on the MTF-50 scores and the percent difference between them?

Next, why would we sharpen both files equally (whatever that means)? For example, we wouldn't sharpen a file from the D800 the same as a file from the D800E, would we?

So, the purpose of this thread is to determine under what circumstances MTF-50 scores are an accurate measure of the differences between systems (not the lenses, per se, but the systems), and, as a corallary, why lens test sites do not test in this manner.

Canon EOS 50D Nikon D800 Nikon D800E
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