Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions thread
knickerhawk Veteran Member • Posts: 5,159
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Just another Canon shooter wrote:

knickerhawk wrote:

But look what happens when we set the respective dxo score maps at equivalent aperture settings:

That tells a rather different story than the basic score, doesn't it?

It tells you the story about a company which decided to dumb down the way to present their measurements in order to appeal to the "ordinary public"; in a rather successful way, apparently.

Remember, the reason I responded to Bob was to counter his criticism of Anders for not accepting at face value the "packaged" results from DXO.  I think you and I are actually pretty much in agreement on the questionable value of DXO's scores.  Likewise, I think we probably agree that the dumbing down of the lens data and packaging the data introduces unfortunate problems.  A naive reading of the scores (and score maps) fails to take some important factors (such as equivalence) into account and a more sophisticated reading of the scores appears to be impractical.  It's a shame really because there's a lot of useful data underlying these scores, maps and profiles.

Did you notice that those charts are "accutance maps", whatever DXO means by that, measured in percentage of something (DXO decides that it is too much to tell us because they believe that we are not intelligent enough to understand it)? If you compare them in another undocumented metric, P-Mpix, those charts look like this:

12-40 on EM-1 vs. Nikon 24-70 on Df. The f-stop scale is in m43 eq. units

What does it tell us (in the Mpix metric)? First, the m43 combo has a huge gap - cannot do f/2.8-f/5.6 (the vertical axis is in m43 units, not FF ones). Of course, we knew that but this is the elephant in the room which should be noticed from time to time. Next, in the aperture range that the m43 combo can do, it is mediocre. In the very wide end kinda gets close somewhere around f/5.6 (in FF terms) and that's about it.

Your reference to the P-Mpix maps is just another example of how misleading the presentation of the DXO data can be.  For instance, the information in the sharpness profile tab for the two lenses at f/2.8 for the Oly and f/5.6 for the Nikkor indicates that they perform quite similarly in the center (the Oly wins the horizontal measurement and the Nikkor wins the vertical and average of the two), but the Oly is better across the whole frame.  However, because the DXO P-Mpix score weights (in some unspecified way) center performance more than performance outside of the center, the 24-70 appears in the map to be a stronger performer.  Interestingly, the Panny 12-35mm has a slightly stronger (equivalent) center performance than either of the other two zooms being considered here, so it's not as if there is some insurmountable limitation on center accutance for the smaller format.

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