Do you always want a low distortion UWA?

[bakubo]

Something that I have thought about off and on for the last few years concerns the "distortion" of ultra-wide angle lenses. Those with less distortion generally cost more since it is usually a prized attribute, but I have noticed that with my Sony 11-18mm and Sigma 10-20mm lenses that even though I can use PTLens to correct the distortion there are times when I choose not to. Usually it is when there are people near the edge of the frame. Without correction they look reasonably natural, but with correction they are stretched and elongated. I wonder if lens designers actually consider this during the design? Of course, when you are photographing things with lines, such as a building, it usually looks better without the distortion. Over the years I have had some great examples, but this afternoon I was working on a few photos that display it reasonably well also -- just not as well as some in the past. When the people are even nearer the edge it is more pronounced. Take a look. The first photo has not been corrected with PTLens. The second has.

[Greg Beetham]

Henry, I see very little difference between the two, distortion wise...what am I supposed to be looking for?
Greg

[Birma]

I think the difference is pretty subtle in this example - the two people near the edges of the frame do appear more natrual (less stretched) in the first one. The building in the background on the right are still leaning back a long way in both shots so I guss it is only a small correction. I agree with the concept though - other that when trying to get architecture to line up properly the UWA effect is not unpleasant in my eyes.

[harveyzone]

A rectilinear wide angle lens distorts the corners of an image. That is what it is designed to do - to make things that would converge as they move away from you stay parallel. What you are seeing is what stops it being a fish-eye type wide angle lens.

PTLens does not correct these types of distortions. It corrects slight barreling, pincushioning or more complex distortions that are not supposed to be there. It does not correct the stretching on the edges/corners that the lens is designed to produce.

[KevinBarrett]

I'd say that if you only have lines converging on the center of the frame, you might as well invite as much "barrel" as the composition will handle.

[bakubo]

My point is that I wonder if they consider this when designing a lens and intentionally allow it to distort? For people and some other things a "distorted" view gives a more natural look to people than an "undistorted" view. It makes me wonder something else. If you have a very expensive lens with much less distortion is there an easy way (as easy as PTLens) to put distortion back in so that people near the edges don't look distorted?

Although I have seen this most with ultra-wides, I think, I have seen it to a lesser degree occasionally even with lenses that just go down to 18mm (such as 18-250mm).

[harveyzone]

My point is that I wonder if they consider this when designing a lens and intentionally allow it to distort?

They have to - it is these distortions that keep straight lines straight when parallel with the sensor. The choice is to have curved lines (like a fish eye) or to 'correct' these by stretching the corners.

For people and some other things a "distorted" view gives a more natural look to people than an "undistorted" view. It makes me wonder something else. If you have a very expensive lens with much less distortion is there an easy way (as easy as PTLens) to put distortion back in so that people near the edges don't look distorted?

An expensive lens will have a similar amount of distortion. This is how the lens has been designed. You can make it look more natural by putting some Barrel distortion back in to reproduce perspective. Here is the same image with a small amount of Barrel applied...

Although I have seen this most with ultra-wides, I think, I have seen it to a lesser degree occasionally even with lenses that just go down to 18mm (such as 18-250mm).

It will happen with all lenses that try to keep straight lines straight. It is just not that obvious on longer lenses, as the distortions are far less.

[David Kilpatrick]

PTLens will do a better job using Cylindrical Distortion instead of barrel - keeps the horizon straight, but reduces the face-stretching.

David

[01af]

My point is that I wonder if they consider this when designing a lens and intentionally allow it to distort? For people and some other things a "distorted" view gives a more natural look to people than an "undistorted" view.

Yes indeed. As a matter of fact, any decent wide-angle lens distorts on purpose. They don't distort because the lens designer was too dumb to understand how to design a distortion-free lens. Instead, the degree of residual distortion is very carefully and purposefully balanced with a whole bunch of properties. Accepting a bit of barrel-shape distortion in a wide-angle or standard lens will

• reduce projectional distortion (i. e. "face streching")
• reduce both natural and artificial vignetting
• reduce lens' size and weight
• reduce price

It's said when correcting an image for converging verticals then you should leave a tiny bit of convergence because it will look more natural to the eye than a perfectly straight image. Well, it's the same with distortion. A wide-angle image with a tiny bit of barrel-shape distortion will look more natural to the eye than a perfectly distortion-free image ... usually (not always, depends on subject).

It makes me wonder something else. If you have a very expensive lens with much less distortion is there an easy way (as easy as PTLens) to put distortion back in so that people near the edges don't look distorted?

Sure! Any software that can remove/reduce barrel-shape or pincushion-shape distortion also can do the contrary, i. e. add some distortion, and thus reduce "face stretching" (or the stretching of any kind of forms and shapes near the frame's edges, at the expense of increased barrel-shape distortion, see Tom's version of your image above).

It's impossible to map a three-dimensional world into a two-dimensional image in a distortion-free way. You will always get some sort of distortion; that's an intrinsic rule of geometry. That's why it's nonsense to say, a fish-eye lens distorts and a wide-angle lens doesn't. Actually, both do distort, but in different ways; the wide-angle's straight lines come at a price. All you can do is trade one kind of distortion for another, depending on your preference for a given subject. And with digital image processing, the choice is yours.

-- Olaf

[bakubo]

PTLens will do a better job using Cylindrical Distortion instead of barrel - keeps the horizon straight, but reduces the face-stretching.

PTLens only gives the choice of barrel/pincushion and fisheye correction, not cylindrical.

[bakubo]

Olaf and everyone else, thanks for your replies.

I am busy each day working on the Egypt trip photos because I would like to finish and get some put on my website before we head to Tokyo. I have been late in coming back to this thread because of that and also the shoulder/arm problem. Because Japan pretty much closes down for o-shogatsu I wasn't able to go see a doctor until yesterday. It is pretty much what I thought and there is not much that can be done about it other than wait until it gets better on its own. Very painful and the ibuprofen only helps a little. Not getting much sleep.

[Greg Beetham]

What's the deal with the sholder/arm problem Henry?
Greg

[bakubo]

What's the deal with the sholder/arm problem Henry?

A bit over a week ago, about Christmas Day or Christmas Eve, while still in Egypt I noticed that my right arm hurt a bit, but it wasn't bothering me much and about the only time I noticed it was when I used the mouse on the computer. A few days later I was back in Japan and the pain had increased significantly going from my neck and most of the way down my right arm, but with the center of the pain in my shoulder. My guess was that I had a pinched nerve in my neck. It was o-shogatsu (New Year holidays) in Japan though and pretty much nothing happens for a week or so. Except for an emergency room the hospitals, clinics, and doctors' offices were closed. Finally on January 4th a few reopened so first thing in the morning we went to the hospital. The doctor was a really good guy, maybe 2-3 years older than me, and he did an examination and asked lots of questions. He didn't think it was a cervical herniated disk so didn't order an MRI, but I did get x-rays done. It was pretty much what I had thought. He showed me how the gap between 2 of the vertebrae in my neck was a bit narrower than the others and how the opening of the right side where the nerve goes out was a bit constricted compared to the others. He is pretty sure that the nerve is getting pinched a bit there. He said that my x-ray is totally typical for someone my age though and, in fact, he has had the same problem off and on for the last few years. He said it would probably get better on its own after a few weeks or months. I can tell you that at its worst it hurts so much I can hardly think of anything else, but the ibuprofen and heat help some. When I get back to the States, if I still have it, I will probably see another doctor and just see what he says.

[David Kilpatrick]

I have had something like this after a fall. A chiropractor - most of it mumbo-jumbo frankly - yanked my neck/shoulder alignment back and it went away. It actually worked very quickly, the first session. I had signed up for a year... I don't think the later fortnightly then monthly treatments did as much good, I think could 'see' the misalignment (no X-rays at all) and knew how to manipulate to cure the problem.

David

[bakubo]

Over the years I have been to chiropractors a few times -- sometimes with good results, sometimes with not so good results. In my experience they either make it better or make it worse, but rarely do you leave in the same condition you came in.

One of the great things about Japan is the onsen and the whole Japanese onsen culture. Whenever I am in Japan I always accept any invitations to go to one. My wife went to a new one with her mother while I was in Egypt and she suggested we go there today because it is an especially nice one. It also has a big room with comfortable recliners and individual LCD TVs that you can relax in between baths. Of course, besides the various indoor onsen pools of various temperatures they had several rotemburo (outdoors onsen). They have big digital thermometers next to each one and most were 41-43C, but one was 45C and another was 19C. The air temperature outside was about 6C. I didn't get in the 19C one.

We were there for about 5 hours and bathed and relaxed 3 times in the onsen and also I watched a movie on the movie channel. The Japanese do onsen better than anyplace in the world. Here is the place we went today:

http://www.soratomori.jp/

The warmth made my shoulder and arm feel much better.