Clarification on DXO scores raises more ? than answers

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terryreid
terryreid Senior Member • Posts: 1,553
Clarification on DXO scores raises more ? than answers

On the APS-C forum there was some debate on the sharpness of the new 24-135 lens.

The DXO scores on the 85GM lens are over three times higher on a a7rII vs an a6000 yet ony a 16 point difference (hardly triple) between the two cameras. The sensor score on a a6000 is 82 (85 for a6500) vs 98 for a7rII. I don't think anyone would dispute these scores.

However the 85 1.4 GM is rated by DXOmark at 11 for sharpness on a a6000 vs 39 on a a7rII.

Obviously there is more at play than I probably most others understand. I guess the obvious question is how these scores are compiled to have such a huge descrepency on lens/camera combinations.

This gentlemans' explanation show if it is correct that the difference between a a6000 and a7rII as only being 1.2 stops and a a6500 and a7rII being 1 stop.

Now I am really confused and it appears that the scores would not mean as much as one would think but I kind of disagree based on my own experience with different lenses.

In my way (flawed perhaps) 1 stop means a a6500 compared to a a7rII is like it being set to ISO 200 vs ISO 100 but there has to be more to it than that IMO.

While we are at it can someone explain how 1 stop affects

sharpness

noise

what the image looks like

With all the confusion on DXO scores I know I could sure use some clarification. At first glance I wanted to return the a6500 I just replaced my other one with I have no desire to shoot with a FF lens that gets knocked down to a third. I am going to shoot some test screens for myself with both the a7rIII and a6500 w 85GM also.

The other thing I thought of is does the crop sensor camera somehow degrade the image of FF lens to bring it down to less than a third of its FF score. If so why is the a6500 and 70-300 G such a popular BIF setup.

Can anyone explain in laymans terms how these scores can be so different for the same lens and how that affects the image one gets from each camera what you might notice and when.

Also how 1 stop comes in to play on image IQ

This is the explanation on that tread and he had dxo links that bore this out.

I think it would be valuable to all of us to understand how these scores represent what we will see in our images and prints. I have had a a6500 before and the discrepancy in IQ is not as large as DXOmark's scores would indicate. Granted the a6500 camera score is 85 vs 82 for the a6000 its close enough.

  • The Sensor Overall Score is logarithmic: A 5-point difference on the scale corresponds to again or loss of sensitivity of 1/3 of a stop.
  • The Sensor Overall Score is normalized for a defined printing scenario of 8 Megapixels printed on a 8×12-inch (20cm x 30cm) size at 300 dpi resolution. Any other normalization, even at a higher resolution, would lead to the same ranking, given that any camera that cannot deliver the chosen resolution is eliminated from the comparison.

https://www.dxomark.com/dxomark-camera-sensor-testing-protocol-and-scores/

The a6500 is rated less than 1/3 stop higher than an a6000. The A7R II sensor scores 100, which is (100 - 82) / 5 / 3 = 1.2 stops better than the a6000, one stop better than the a6500.

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-Terry

 terryreid's gear list:terryreid's gear list
Sony RX100 V Sony a9 Sony FE 90mm F2.8 macro Sony FE 85mm F1.4 GM Sony FE 50mm F1.4 ZA +16 more
Sony a6000 Sony a6500 Sony Alpha a7R II
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