14mm f2.8 zero distortion??

[petergabriel]

Help me understand what is meant by distortion when sites like lenstip.com rate the Fujinon 14mm f2.8 truly impressive, because it has virtually no distortion, and yet, when I look at the group shot of the girls on this blog, the girl on the left edge of the frame hopefully does not like that in the real world. It looks like she is being somehow stretched towards the upper left corner. Why is that?

 

 

 

Edited June 20, 2016 by petergabriel

[aceflibble]

Depends how they've been processed, and how the lens was measured/tested. Some people only consider distortion to be warping beyond what you expect from a particular angle of view. For instance, the compression you get from a 200mm+ lens used for a portrait isn't considered 'distortion', even though it isn't a true representation of the subject. Similarly, some people expect a wide-angle lens to spread out the sides and corners of an image, so they don't consider that to be an error, either. In that sense, that example photo is quite distortion-free. Wide-angle lenses often suffer from barrel distortion, but that image doesn't buldge in at the middle, so someone looking for barrel distortion might consider that image to be free from faults.

With Fuji lenses things are made more complicated because you can't mount them to other companies' bodies for testing, and Fuji's own bodies always apply a range of corrections—including distortion correction—to the images. You can turn that feature off, but it is never fully off, and it's on by default. Most raw convertors will also include these corrections by default. So you could have a case where one person simply uses everything with the default settings, and sees no distortion, but another person may have taken the time to disable all those corrections and will see some distortion.

Fuji lenses are also flat field designs, which doesn't have anything to do with distortion from a technical point of view, but it does change how you use the lens and frame subjects for sharpest focus, which in turn may help minimise distortion compared to how you'd frame the scene if you were using a curved field lens. Basically, people using Fuji cameras tend to be more aware of keep the camera perfectly upright and straight, whereas someone using something like a Canon or Sony might not be so careful and very slightly tilt the camera, which could then exaggerate some distortions.

 

 

tl;dr: If you look at images from the lens and you see distortions, they're distortions. If you look at images from the lens and don't notice any distortions, it's distortion-free. What you define as distortion and how much you're willing to accept or notice is entirely subjective. There's no such thing as a lens which is truly 100% technically distortion-free, but different people have different standards and expect/will allow different types and degrees of distortion for different focal lengths.

[CRAusmus]

Here's a shot I took on the 16th at the Trump Protest with the 14 ƒ2.8.  These guys were just a few feet away from me when I snapped it.

 

 

I could have squared up a little better, but you can see there is little to no distortion.  I love the 14.  I'm so happy I bought it.  Taken on the X-T1 if it matters.  Processed in LR CC 2015.  only adjustments were contrast and profile set to Pro Neg Hi.

Edited June 20, 2016 by CRAusmus

[petergabriel]

Depends how they've been processed, and how the lens was measured/tested. Some people only consider distortion to be warping beyond what you expect from a particular angle of view. For instance, the compression you get from a 200mm+ lens used for a portrait isn't considered 'distortion', even though it isn't a true representation of the subject. Similarly, some people expect a wide-angle lens to spread out the sides and corners of an image, so they don't consider that to be an error, either. In that sense, that example photo is quite distortion-free. Wide-angle lenses often suffer from barrel distortion, but that image doesn't buldge in at the middle, so someone looking for barrel distortion might consider that image to be free from faults.

 

With Fuji lenses things are made more complicated because you can't mount them to other companies' bodies for testing, and Fuji's own bodies always apply a range of corrections—including distortion correction—to the images. You can turn that feature off, but it is never fully off, and it's on by default. Most raw convertors will also include these corrections by default. So you could have a case where one person simply uses everything with the default settings, and sees no distortion, but another person may have taken the time to disable all those corrections and will see some distortion.

 

Fuji lenses are also flat field designs, which doesn't have anything to do with distortion from a technical point of view, but it does change how you use the lens and frame subjects for sharpest focus, which in turn may help minimise distortion compared to how you'd frame the scene if you were using a curved field lens. Basically, people using Fuji cameras tend to be more aware of keep the camera perfectly upright and straight, whereas someone using something like a Canon or Sony might not be so careful and very slightly tilt the camera, which could then exaggerate some distortions.

 

 

tl;dr: If you look at images from the lens and you see distortions, they're distortions. If you look at images from the lens and don't notice any distortions, it's distortion-free. What you define as distortion and how much you're willing to accept or notice is entirely subjective. There's no such thing as a lens which is truly 100% technically distortion-free, but different people have different standards and expect/will allow different types and degrees of distortion for different focal lengths.

 

Thank you for the explanation:-) But wouldn't you agree that the girl in the red dress to the left looks strangely stretched?

 

The 14mm should be optically distortion free, no (minimal) software corrections, as opposed to e.g. the 18mm f2.0

Edited June 20, 2016 by petergabriel

[mdm]

I've bought mine after I saw this one - https://florianziegler.com/sheikh-zayed-grand-mosque/

[flysurfer]

Help me understand what is meant by distortion when sites like lenstip.com rate the Fujinon 14mm f2.8 truly impressive, because it has virtually no distortion, and yet, when I look at the group shot of the girls on this blog, the girl on the left edge of the frame hopefully does not like that in the real world. It looks like she is being somehow stretched towards the upper left corner. Why is that?

 

 

 

 

 

I don't see any distortion here. Just volume deformation. 

 

As our friends at DxO put it: "In practice, the principles of optical geometry dictate that it is impossible to maintain both straight lines and volume consistency."

[petergabriel]

I don't see any distortion here. Just volume deformation. 

 

As our friends at DxO put it: "In practice, the principles of optical geometry dictate that it is impossible to maintain both straight lines and volume consistency."[/size]

Volume deformation? Care to explain. :-)

[Marc G.]

I look at that picture and the only thing I can see is a crime committed by the photographer.

[c0ldc0ne]

Volume deformation? Care to explain. :-)

 

 

Here you go: http://www.dxo.com/us/photography/tutorials/understanding-volume-deformation

[petergabriel]

Here you go: http://www.dxo.com/us/photography/tutorials/understanding-volume-deformation

Thanks. Just found that article myself. So I guess the 14mm is not for group shots then :-)

[c0ldc0ne]

This is an inherent property of any rectilinear UWA lens. You either need to make sure that you don't place your subject too close to the edge of the frame, use a lens with a longer focal length and back up or use a lens (or post processing technique) with a different projection.

[Marc G.]

Just don't go wider than 23mm and you're fine.

[deva]

that photo looks funny... as if the whole image was squeezed a bit horizontally to make them look skinnier. 

[bhu]

All lenses have some form of distortion. If the distortion can be corrected using a mathematical transform, whether in-camera or using software, then it is distortion-free.

 

There are other types of aberration that are not correctable. For example, a lens element may not be polished to perfectly match the ideal design/shape and so distortion correction software (based upon an ideal lens) does not fully correct for that particular lens' distortion (and other aberrations).

 

That group photo can be warped mathematically to "fix" the barrel distortion, both spatial and luminance, but the SW needs to have a filter for the ideal Fujinon XF14 and the actual lens should be very close to that ideal.

[petergabriel]

I don't see any distortion here. Just volume deformation. 

 

As our friends at DxO put it: "In practice, the principles of optical geometry dictate that it is impossible to maintain both straight lines and volume consistency."

 

Volume deformation, is this something that is only seen from a given focal length? As seen it is there on a 14mm, but what about a 16mm? 

[petergabriel]

Found the answer myself. It appears that 16mm (aps-c) is the threshold.

 

The sensitivity threshold is estimated to be about 15%, or in other words, a focal length of 24mm (eq. 24 x 36 mm); deformation above 25% (which appears below 17mm, eq. 24 x 36 mm), the problem is considered too big to avoid correcting. From DxO

Edited June 25, 2016 by petergabriel

[frod]

The only way you can avoid that kind of distortion is to use a fisheye and print onto the inside of a sphere

[rquindry]

If you were to make a large print and put your eyes close enough to it so that the angle viewing the print matched the angle of the lens, I believe it would look fine.

 

DxO makes a plug-in for Photoshop (which also comes as a standalone) that is deigned to reduce the effect of volume deformation. It's called DxO Viewpoint.

 

Here is your image after running it through that plug-in with settings that I chose. You can decide if it's improved it enough.

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