Reading resolution charts comparing MFT lenses to FX lenses

Started Mar 29, 2013 | Questions thread
KenBalbari
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Re: Reading resolution charts comparing MFT lenses to FX lenses
In reply to Dr_Jon, Mar 29, 2013

Dr_Jon wrote:

Err, no, I think I must disagree. 50lp/mm over a 10mm sensor is 500lp of detail which most sensors would easily resolve. 80lp/mm over a 3mm sensor is only 240lp (in the picture height) so lower resolution even if you have a sensor that could resolve 1000lp/mm. It's lp/mm and the mm over which it manages it that gives sharpness, regardless of the sensor (as long as it's in the ball park, no 2x2 pixel systems need apply).

Actually, I think you are agreeing.  That's pretty much exactly what I was saying.

My only point with lp/mm is that it is useful for the original posters question.  As I made clear, this is ignoring sensor performance and final image quality.  That's a pretty significant qualification, and those are things you obviously wouldn't ignore if comparing cameras or systems.

If you look above though, where Prairie Pal clarifies his question, he says:


"I think I was asking whether a "conversion formula" could be applied for comparing the relative ranking of a specific MFT lens within its peers to the ranking of a specific FX (or DX for that matter) lens within its peers.  Furthermore, I would like to understand if the performance of a number FX/DX legacy glass on thier respective sensors maintain their ranking when adapted to MFT, AND whether they outperform the current MFT lens offerings."


This is where I think lp/mm can come in handy.  Though I think it's really only useful when you have a tester who tests various lenses, from different systems, all on the same test bench.  Trying to convert between tests on different cameras isn't going to be as reliable.  Worth knowing more just to understand what is being measured.

For the photozone tests, for example, if you look at the Nikon 35mm f/1.4 G lens, they actually tested that on both a D3x (full frame) and  D7000 (APS-C).  That might help to see how the MTF results "translate" between two different formats.    On the D3X, the top of the chart, which they consider roughly the maximum possible MTF for the D3X, is 4000 lw/ph, and "excellent" is from 3450-4000.  On the D7000, the maximum on their chart is 2900 lw/ph, and "excellent" is from 2500-2900.  The lens is generally "excellent" in the center, and "very good" at the edges from f2.8 down.

As to how it would perform on the OM-D, I'd say very similarly to the D7000, since that camera test very similarly in overall resolution. Per DP Review resolution tests:

"Whereas in the JPEG files, the D7000 cannot accurately describe the 9 lines on our test chart much beyond 2600LPH (roughly), the RAW file still shows all nine lines distinctly at 2600LPH, and they only begin to merge at around 2800LPH." ( link )

"At first glance the E-M5's JPEGs give the impression of being able to render 2800 lines per picture height. This is essentially impossible and closer examination shows the last point at which it clearly differentiates between the lines is actually nearer 2600 (which is what you'd expect of a sensor of this resolution)."  ( link )

One thing to note is that the two scales (DPR and PZ) here are not comparable, as DP review is not using an  MTF50 definition of resolution.  Also, the DPR test is also influenced by the lenses they use, though they do try to pick one of the sharpest available for a camera, in order to get close to the maximum for the sensor.

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