Lens correction settings gets ignored

[NotMyFault]

Hi,

when toggling lens correction on/off, the scale setting reverts to 0 but stays on e.g. -50%.

if you touch the scale setting, rendering will again reflect the slider value.

 

[MEB]

Hi @NotMyFault,
I'm not sure I understood you. Were you expecting that after setting the scale to 50% then turning off the Lens correction the scale slider value would go back to 100% (since the image is no longer being corrected)?
 

[NotMyFault]

I would expect that the slider value and the rendered scale always match. 
in this case, the slider stays at 50%, but the actual rendered scale reverts back to 100%. This is an UI inconsistency and very annoying. I would prefer to keep the scale at 50% to allow checking the effect of lens correction. At 100% zoom the effect is difficult to spot because the barrel extends in the middle of the edges, but this is always cropped off when toggling lens correction. 
 

[MEB]

Hi @NotMyFault,
Thanks for confirming/additional info. As far as I'm aware this is by design. If the sliders (not just Scale since this affects all of them, including other controls from the rest of the Develop tabs) would always match what's displayed on screen then there wouldn't be a reason to have a toggle at all. The intended use of the toggle is to be able to compare the adjustments you are performing with the original state of the image (when the toggle is set to OFF) or disable them temporarily for some reason keeping its settings. You also find similar behaviour in the Layer Effects where you can toggle each effect on/off without the sliders being affected/changed).

I understand what you are looking for but changing the Scale in the Lens Correction tab to be able to verify the effect of lens correction (barrel effects) is just a "hack" you are using to get there, not a solution for the specific issue you are raising (also because it would introduce inconsistency between the controls in the various Develop tabs etc).

Maybe a checkbox to display the whole image with the cropped parts shaded, a bit like what you have when you are applying a crop, so you can see the extent of changes besides the image "frame" or something along these lines would be better?
This seems more a feature request/improvement to me than an issue with the scale slider specifically.

[NotMyFault]

2 minutes ago, MEB said:

The intended use of the toggle is to be able to compare the adjustments you are performing with the original state of the image (when the toggle is set to OFF) or disable them temporarily for some reason keeping its settings.

That is interesting. Develop Person has a Split View option to show the modified version side by side or in-place with slider.

It seems i misinterpreted the toggle slider to just deactivate the lensfun-based automatic / lens-specific correction (and not the manual sliders below).

Can be closed.

[MEB]

Yes, the Split View/Mirror does help - I forgot about them - so you already have a way to partially sort it out without using the Scale slider.