Distortion

[JohnP]

Hello:

Some general questions about distortion:

1. Is it correct to say that distortion cannot be avoided on wide angle lenses and that the wider the field of view the greater the distortion?

2. At what focal length does distortion become pronounced?

3. Is distortion of people/places in the foreground equal to that of distortion on the horizon?

4. Is distortion uniform across brands? In other words will the Elmarit 24mm show less distortion than a 24mm lens of a lesser brand?

5. Can distortion be corrected in post-processing (Photoshop)? Always?

Thanks,

John

 

[Matthew Allen]

Hello:

Some general questions about distortion:

1. Is it correct to say that distortion cannot be avoided on wide angle lenses and that the wider the field of view the greater the distortion?

2. At what focal length does distortion become pronounced?

3. Is distortion of people/places in the foreground equal to that of distortion on the horizon?

4. Is distortion uniform across brands? In other words will the Elmarit 24mm show less distortion than a 24mm lens of a lesser brand?

5. Can distortion be corrected in post-processing (Photoshop)? Always?

Thanks,

John

1. With a good prime lens (even a very wide one) distortion should be minimal. With certain compositions however, any ultra wide lens will produce 'stretched' perspective which some people confuse with distortion.

2. There's no meaningful answer to this - distortion depends on far more than just focal length.

3. Depending on the type of distortion it will have different effects. Perspective stretching will be most apparent at the edges of the frame.

4. Every lens design produces slightly different distortion - barrel, pincushion, 'moustache' etc. With a long zoom (e.g. a 28-200) you will typically see both barrel and pincushion distortions at different focal lengths.

5. There are specially designed programs for correcting distortion like PTLens, DxO etc. Not sure about PS as I don't use it myself.

Matthew

 

[ampguy]

answers

answers

1. Yes, and Yes. But for the 2nd part of this question, it is because of the increased difficulty in designing a rectilinear lens as the fov increases. I am defnining rectilinear as:

rendering all straight lines in the subject as straight lines in the image

2. Depends on the lens design, and angle taken of the subjects, if you're talking about wide angle distortion, it is generally more visible with wider fov lenses. With 35mm film size/ff sensor, most 35mm and wider lenses, exhibit this distortion, with better lenses exhibiting more rectilinear than others. Prior to the 35mm ASPH Cron, which has minimal distortion, less so than many 50mm "normal" lenses, many people relied on 50mm lenses as their standard lens, not necessarily for the field of view, which can be tight, but for the fact that lens makers often had the least distortion at this focal length in their products.

3. Please define your definition of distortion on the horizon.

4. No, it is not the same across makes, models, or brands. Some brands and samples have less than others. It is complex to test, as they will vary by aperture and angle to subject.

5. No, not perfectly. It can visibly make make some wide angle distortion photos (including fisheye lenses) appear semi-rectilinear.

Hello:

Some general questions about distortion:

1. Is it correct to say that distortion cannot be avoided on wide angle lenses and that the wider the field of view the greater the distortion?

2. At what focal length does distortion become pronounced?

3. Is distortion of people/places in the foreground equal to that of distortion on the horizon?

4. Is distortion uniform across brands? In other words will the Elmarit 24mm show less distortion than a 24mm lens of a lesser brand?

5. Can distortion be corrected in post-processing (Photoshop)? Always?

Thanks,

John

 

[Andrew3511]

The stretching of objects at the edge of the frame with wide angle lenses will become apparent with 28mm lenses and is very noticeable with a 21mm. It is a consequence of geometry. If a print is enlarged to the right size and viewed from the distance which gives the same angle of view as the taking lens (so viewing a 12x18 inch print taken with a 21mm at about 10 inches) this distortion disappears. Pincushion and barrel distortion are lens aberrations and can be corrected in post-processing and are sometimes affected by focussing distance, especially in lenses with floating elements to correct other aberrations at close focussing distances.

 

[rxmd]

Minor extra comments:

3. Is distortion of people/places in the foreground equal to that of distortion on the horizon?

The relationship here is strictly geometric. Both wideangle "stretching" and distortion from lens aberration depend on the position of the object in the frame. The distance to the subject is irrelevant in so far as an object in the background will show the same amount of distortion as an object in the foreground, provided that the background object is big enough to compare the two. (We are talking about wideangles, so objects on the horizon would usually have to be really big.) But yes, a mountain in the background will be distorted as much as a head in the foreground if both are at the edge of the frame.

4. Is distortion uniform across brands? In other words will the Elmarit 24mm show less distortion than a 24mm lens of a lesser brand?

Wide-angle "stretching" will be completely equal because it is only a result of geometry.

Lens aberrations are lens-specific. Incidentally the concept of a "lesser brand" may or may not translate into inferior performance with respect to specific optical characteristics. A "lesser" Zeiss Biogon 21/f4.5 beats anything Leica has to offer on aberrations. Whether or not that makes your pictures better is another question.

Your framing with a rangefinder is likely to be much less accurate than the projection of the lens. If you absolutely depend on having distortion-free wideangle pictures, such as for architecture, it might be more important to use an appropriate camera that will allow you more control over framing and perspective, such as an SLR or a view camera. If you just want an everyday lens, all modern lenses are so good here that this is nothing to worry about. Don't believe Internet hypes.

5. Can distortion be corrected in post-processing (Photoshop)? Always?

Wide-angle "stretching": no. You can, however, use tools such as PanoTools/Hugin to convert your picture from rectilinear projection to other projections, such as equirectangular "panoramic" projection, which will make the stretching less apparent.

Distortion from lens aberrations: yes, using tools such as DxO or PTLens, but it can be tricky to get the parameters for RF lenses.

Philipp

 

[pvdhaar]

Just as an aside, the lenses with the least distortion aren't always the best for every application. If you're shooting architecture, then sure, you want straight lines to come out straight. But for photojournalism you'll want a wide angle with a bit of barrel distortion to minimise the 'elongated heads' effect that you get at the sides of the frame..

The 'elongated heads' effect is because a completely recitilinear lens needs to work against perspective to correct for converging lines away from the center of the frame..

 

[visiondr]

A "lesser" Zeiss Biogon 21/f4.5 beats anything Leica has to offer on aberrations....Philipp

Prove it!?
Yes, the Biogon 21/4.5 has great numbers when it comes to low pincushion or barrel distortion. But, that's very different animal from 1st, 2nd and 3rd order aberrations.

 

[Chris101]

To cure "wide angle distortion" stand closer to the prints.

 

[visiondr]

I know that sounds goofy, but Chris is right. If you stand "into the space" of a wide angle photo, you'll the see the world as the lens "saw" it when the shutter opened. It's a cool effect, especially with a large print.

 

[ampguy]

good point

good point

as the lens saw it, but not like the eyes saw it through a rectilinear VF.

I know that sounds goofy, but Chris is right. If you stand "into the space" of a wide angle photo, you'll the see the world as the lens "saw" it when the shutter opened. It's a cool effect, especially with a large print.

 

[Sparrow]

All lenses “distort” the same amount, they all take a 3D world and map it onto a 2D image.

You can have a fisheye that bends the image but keeps the relationships of the image’s elements each to the other the same, or at the other extreme a rectilinear lens that keeps the image straight and changes the elements relative position.

Either way the distortion is the same, just like it is with maps, if you want distortion free you would need a hemispherical print

 

[rxmd]

Yes, the Biogon 21/4.5 has great numbers when it comes to low pincushion or barrel distortion. But, that's very different animal from 1st, 2nd and 3rd order aberrations.

I'm aware of that. I was really referring mainly to pincushion & barrel distortion.

I am also aware of my somewhat sloppy use of terminology. These are technically not "aberrations" in the strict sense of the word, just like wideangle stretching is not "distortion" in the strict sense of the word but just the result of perspectivic projection. The OP was mainly interested in distortion, which is where the lens is really good in spite of being from a supposedly "lesser" brand. That was my whole point.

Philipp