Author Topic: Focal length and Focal distance in both PhotoLab and OP 11  (Read 768 times)

zed

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Focal length and Focal distance in both PhotoLab and OP 11
« on: October 27, 2017, 04:44:51 am »
Win 10 PC user.

Only really used PRIME occasionally and Geometry/ViewPoint for UWA lens distortions.

I never see the Focal distance slider - presumably because none of my cameras are saving it as EXIF data?

When I do see Focal length adjusting it doesn't seem to produce visible changes even at 400% - should it be noticeable?

If the EXIF data says 8mm shouldn't the slider range be 7.5-8.5mm and not 8-9mm? DxO only seems to be offering an adjustment for a low focal length not catering for a possible high recorded value?

Zed

MarieC

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Re: Focal length and Focal distance in both PhotoLab and OP 11
« Reply #1 on: October 27, 2017, 02:55:26 pm »
Hello zed,

Here are some explanation about focal slider.
In Exif focal length are not always accurate, for example on a 16-35mm focal 17mm can not be differentiated from 16mm or on  a 70-200mm, focal 150mm can be recorded as 135mm.
When and only when this ambiguity of focal length is a problem for correction of distorsion we give access to a slider to refine focal value.

On a 70-200mm, with images at 150mm,  we won't have to give access to the slider as distorsion doesn't change much in that focal range.
On a 16-35mm distorsion varies a lot for short focal length so we have to povide access to the slider.

Slider will give a range to refine focal value between "focal of Exif - 1mm" and "focal of Exif + 1mm".
If focal is the minimum of the lens then range will be : "focal of Exif" and "focal of Exif + 1mm".

zed

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Re: Focal length and Focal distance in both PhotoLab and OP 11
« Reply #2 on: October 28, 2017, 08:06:30 pm »
Thanks very much Marie-Catherine - you explained it very clearly. I have a Sigma 8-16mm lens so will be able to experiment with that a bit to see what I can see !

Thanks again,

Zed

 

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