GX7 Lens Review on DxO

Started Dec 15, 2013 | Discussions thread
Steen Bay Veteran Member • Posts: 6,978
Re: DxO's Comments on this...Strong AA Filter?

Anders W wrote:

Steen Bay wrote:

Anders W wrote:

MarkyM wrote:

Emilie from DxO has commented on their site saying they "guess" it is a strong AA filter:

"Yes, this is something we checked many times before publish it,...
Sharpness measured on GX7 is a bit low, but pretty close to the GX1 results. We guess there is a strong Anti Alias filter on this cameras."

It seems to me they did something wrong or had a bad unit.

Strong AA filter as an explanation for this kind of discrepancy (worst results for any MFT camera ever tested, including all those with 12 MP sensors)? No way. If that had actually been the case (which is of course extremely unlikely in the first place), it would have been known long ago. Several test sites (inluding SLR Gear/Imaging Resources and optyczne.pl, the Polish counterpart) have looked at the resolution of the sensor without finding anything unusual.

So DxO made a mistake or had a faulty unit. What is really weird is that they went ahead and published the results in spite of the fact that something is clearly wrong.

Checked.. DxO has tested 29 different mFT lenses on 13 different mFT cameras (+ a few older lenses only on older cameras), and with every single of the 29 lenses the GX7 gets a very low score. Makes me wonder... mistakes happen, but 29 times in a row! Could it be that they don't actually test every single lens on every single body, but instead use the test result from one camera to derive/calculate the 'results' for all the other cameras?

No, I wouldn't think they'd dare to go that far (or that it is possible to do so "safely").

Hope they don't dare, but doing it the proper/correct way means lots of hard work.

"For each focal length and aperture of the lens, we take pictures at 60 different focusing positions around the focusing point set by the camera's autofocus system. We then use the sharpest image to measure the camera’s MTF."


60 images for each tested FL and f-stop. That's a lot of images for 29 lenses tested on 13 different cameras, and that's just mFT.

If doing it like that, then it's only necessary to test a single 'reference' lens on a new camera like the GX7. Saves a lot of work, but if something goes wrong, then all the derived results will be wrong too.

I initially suspected that they'd run into some kind of shutter-shock problem, perhaps some problem of that kind more or less unique to the particular copy of the camera they tested. On the other hand, one would then expect more problem with vertical than horizontal resolution, and I didn't see anything suggesting that pattern when I had a look. OK, I certainly didn't check very thoroughly but anyway.

It could be something as mundane as a programming error, however. If they entered the wrong parameter/constant when going from their raw observations to the final acutance and P-MPix scores, all the values will of course be off in the same direction.

I am still not sure we can entirely exclude the shutter-shock hypothesis, however. I had a look at the review of the GX7 by optyczne.pl (Lenstip but in Polish) and they apparently ran into a problem with suspiciously low resolution values which forced them to switch to the electronic shutter to get proper values in that department. See here:


Interesting. My Polish ain't that good, but the graph shows clearly that the electronic shutter on GX7 gives sharper images (which shutter speeds?). Seems that the GX1 has a suspiciously low resolution too.

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