Lumix 18-40 Lens Corrections worse on than off??

[Jan.Wedekind]

Hi everyone

I need some help understanding ultra-wide angle distortion and lens correction. I recently got the 18-40 to pair with the S1Rii. Lots of fun, especially with hybrid zoom, since I feel less constrained than just having ultra-wide all the time, for which I don't have a good eye.

But when looking at JPGs SOOC, I am really confused about what I see. Some images just look way too distorted.

So below a top left corner crop from a photo. Exported from LR, one with lens Lens Corrections on, one off. Nevermind the photo, I otherwise don't have anything at hand that is sharp w/o family on it, but I think this suffices to make the point.

With correction ON:

• Panasonic - DC-S1RM2
• LUMIX S 18-40/F4.5-6.3
• 19.0 mm
• ƒ/4.6
• 1/250 sec
• Pattern
• Auto exposure
• ISO 80

Now with corrections OFF:

• Panasonic - DC-S1RM2
• LUMIX S 18-40/F4.5-6.3
• 19.0 mm
• ƒ/4.6
• 1/250 sec
• Pattern
• Auto exposure
• ISO 80

Now, both are obviously distorted. But I find the "corrected" one considerably worse.

Both is at 18mm, crop is from top left corner. The JPG SOOC looks pretty much identical to the LR corrected one (I assume LR uses Pansonic's lens profile)

So several questions:

• Is this just normal at 18mm, mo matter the lens?
• Does this "correction" look right to you?

Thanks for your help!

 

[RuleOfThirds]

Yes, this is normal. Horizontal lines look more straight with correction on, but the correction it self costs a bit of the already low resolution due to the stretching needed. So you have to choose the trade-off you want to apply. Straightend lines vs resolution.

 

[CharlesH]

Is this just normal at 18mm, mo matter the lens?

I have the 18-40 and will take a look later in the week when I’m back home. And I’ll compare it to other ultra wide angles. I think this is normal, but I’m wondering if DxO does a better job. I have DxO Pure Raw as a plugin for Lightroom; it does its own lens corrections, and may handle this somewhat better.

 

[Pete_W]

I agree the uncorrected looks better, Jan. For example the width of the ground floor windows on the left hand side looks stretched in the corrected version.

I process with DxO PhotoLab and haven't noticed strange distortion with the 18-40mm.

 

[GeorgeHudetz]

I think what we are seeing here is the interplay of perspective distion and lens correction. Remember, "distortion correction" only fixes the barrel/pincushion distortion inherent in the lens. It does not fix perspective distortion, which comes from how the lens axis relates to the subject.

It looks to me like the lens axis isn't perpendicular to the front of the building, and thus the windows have differing amounts of skew from left to right (especially clear in the uncorrected version). With UWA, you need to do more than just have the lens level with the ground - you need to have the lens axis perpendicular in both directions to the front of the building if you want to avoid perspective distortion. This is true when you are photographing any flat object, like the front of a building or a painting hanging on the wall, with an UW lens.

Now when we add barrel (lens) correction on top of perspective distortion, things get weird, I agree. For example, look at the lady in the pink dress in the lower left; in the corrected version she looks, um, wider. This stretching interplays with perspective distortion in an unappealing fashion, for sure. At least in this image.

On the other hand, the uncorrected image looks like the building is sagging or frowning. Once you see that, you can't unsee it.

Anyway, that's why it's good to have a distortion correction slider in post; you can choose the "look" that best suits any given image.

Having said all that, it's possible there is a defect in LR, but I'm guessing not.