Focal Length tool and when it appears

I have 2 images, taken with the same {body+lens} … Sony a7 iii & Sony FE Zeiss 16-35.
For one image, the Focal Length tool appears - but, for the other it does not !


As you can see, these shots were taken on the same day - only a few minutes apart.

Quelle en est la raison ?


Hello john
I think this is simply because there is a focal length ambiguity (Exif values are not accurate) around 16mm, but there is no longer a problem at 21mm.
This is why PL asks to specify the value for 16mm.

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There’s a similar effect in DPL’s Mac version: Distance and FL tools are always present, but sometimes, their content is greyed out, which means that DPL was able to determine the settings from metadata.

Depending on the lens, corrections come in ranges that can be seen when e.g. distance is set manually. Distortion correction and others) depends on FL and distance settings. Changing them manually can improve the accuracy of the corrections.

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I think it’s not the first time I provide this info but behavior of focal length slider is not intuitiv and John just wants to have this available for everyone. What is said in this thread is correct but here it is a larger explanation.

So, there is an ambiguous focal length when slider “focal length” is available in pannel “Geometry”.
If there is no declared ambiguous focal in DxO module then slider

  • won’t be present (Windows)
  • will be grayed out (Mac)

Distorsion is mostly dependant of focal length and focusing distance.

The shorter the focal the more distorsion we will have. With a wide angle zoom distorsion can be really different on two focal with only 1mm difference.

Ambiguity focal slider is used to adjust distorsion correction when focal length value in Exif is doubtful.

On a serie of photos shot with the same lens it’s possible the slider is available for some images and not for others. This is because it is determined by the module.

Some zoom lenses can behave like that : several position of the focal ring give images with same information of focal in Exif.

This can be an issue or not. Photos with same Exif but shot at different lens position will have different distorsion measures but it’s not possible to differentiate.

  • if measures are not different enough then it’s not a problem for the correction. Slider won’t be available.
  • if measures are really different then we need to allow users to adjust distorsion correction. Focal is declared as ambiguous in the module with interval [preceding focal in Exif ; following focal in Exif].The module will then do an interpolation of correction of focal available.
  • Note: slider is positionned to the focal declared in Exif. It is the center of the interval but if the ambiguous focal is the minimum focal of the lens then interval is [min focal ; following focal in Exif]



I have the same lens as John (Sony FE Zeiss 16-35 f / 4) and I just checked:
At 16mm, the focal length setting is well displayed, and I no longer have it for other values. As Marie wrote, the distortion correction is quite different between the values 16 and 17 mm. And the Exifs always indicate 16mm while the focal ring is slightly rotated. Therefore, I will watch this point during my next shots with this lens. A strong point of DxO corrections!


Hi Gerarto - - Note: A new Optics Module has been released for this lens; as part of the PLv4.2 update.

The Optics Module will be downloaded/updated automatically, but … you will need to re-export any images taken with this lens in order to take advantage of the new corrections. (I don’t understand why DxO does not make this more widely known ?).

Regards, John M

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