Barrell Distortion

[ChrisBlaze]

Will someone explain if barrel distortion is cause by the crop factor of a camera? If so, do you get barrel distortion on a FF camera?

[gjl711]

Barrel distortion is that fish-eye look, that is the center is more magnified than the edges. It's caused by a hemispherical image being mapped on to a flat plane. The center is bigger. A crop camera will produce less barrel distortion than a FF as you are using the center part of the lens.

[Wilt]

Barrel distortion is not 'caused by a crop' factor. It is caused by a lens. The lens is designed to make a circular image of a certain diameter. A sensor (or piece of film) is put into that image circle. If the sensor is large, it sees the image out closer to the edges. If the sensor is smaller, it sees less of the image out at the edges of the image circle.

When the lens has barrel distortion, it is more likely to be seen to a greater degree out near the outer parts of the image circle, so a larger sensor captures more of the distortion; they smaller sensor sees less of the outer parts of the image circle, and sees mostly the center area where distortions are not so pronounced.

[ChrisBlaze]

so besides PS, is there anything you can do while shooting to prevent or to lessen the effect of barrell distortion.

[SkipD]

so besides PS, is there anything you can do while shooting to prevent or to lessen the effect of barrell distortion.True barrel distortion is a "feature" of a lens. If a lens is manufactured in such a way as to produce barrel distortion, you can do nothing about it except to avoid purchasing that lens.

If the "distortion" you are talking about is, in fact, perspective distortion and not true barrel distortion, there's a lot you can do about it.

We need to get the facts straight prior to continuing this line of thought, though. Are you experiencing some sort of distortion? If so, what does it look like? What, if anything, have you done to test the lens to determine if it is truly distortion in the physical sense as opposed to just a perspective thing?

[ChrisBlaze]

We need to get the facts straight prior to continuing this line of thought, though. Are you experiencing some sort of distortion? If so, what does it look like? What, if anything, have you done to test the lens to determine if it is truly distortion in the physical sense as opposed to just a perspective thing?

well this pictures is one example:

http://chrisblaze.smugmug.com/photos/138456426-L.jpg

I have a lot more pictures that I took with my 17-40mm @ 17mm that are slanted, so I wanted to know if there is something I can do before the shot that will help out.

[SkipD]

What you see is NOT barrel or pincushion (the opposites of each other) distortion. While there may be a tiny bit of one or the other, what you have is essentially a perspective problem because you were too close to the subject and using too wide a lens - assuming you wanted parallel vertical building lines, etc.

The simplest way to correct for this once the image is made (though the results are usually far from perfect in my opinion) is software correction.

The best way to prevent the "distortion", assuming you cannot back up and use a longer lens, is to keep your camera's back vertically oriented (parallel to the building faces) and the lens horizontal (parallel to the earth) instead of pointing the camera's lens up or down. This is where a view camera's advantages really come into play. The lens can be moved up, down, or sideways while still pointing horizontally.

Picking a higher or lower vantage point and keeping the lens parallel to the earth would help a lot with the building edges. However, with a very wide angle view the corners are often stretched out (like in your shot - look at the lower left corner).

By the way - if you used the same focal length on a 35mm film camera (or one of the "full-frame" Canon DSLR's), the effect would be far more exaggerated.

[ChrisBlaze]

What you see is NOT barrel or pincushion (the opposites of each other) distortion. While there may be a tiny bit of one or the other, what you have is essentially a perspective problem because you were too close to the subject and using too wide a lens - assuming you wanted parallel vertical building lines, etc.

The simplest way to correct for this once the image is made (though the results are usually far from perfect in my opinion) is software correction.

The best way to prevent the "distortion", assuming you cannot back up and use a longer lens, is to keep your camera's back vertically oriented (parallel to the building faces) and the lens horizontal (parallel to the earth) instead of pointing the camera's lens up or down. This is where a view camera's advantages really come into play. The lens can be moved up, down, or sideways while still pointing horizontally.

Picking a higher or lower vantage point and keeping the lens parallel to the earth would help a lot with the building edges. However, with a very wide angle view the corners are often stretched out (like in your shot - look at the lower left corner).

By the way - if you used the same focal length on a 35mm film camera (or one of the "full-frame" Canon DSLR's), the effect would be far more exaggerated.


so in other words, instead of pointing up or down to get a shot, I would need to raise or lower the whole camera?

[Wilt]

so in other words, instead of pointing up or down to get a shot, I would need to raise or lower the whole camera?

If you did not have a camera with rise and fall movements (like a view camera) you could raise or lower the entire camera to level where the lens stay perfectly horizontal and the back (or sensor) stays perfectly vertical, with no tilting, in order to avoid the converging lines.

You photo has the opposite effect of the skyscraper than gets narrow as you look up, it is getting narrow as you look DOWN...perspective distortion as was described in another post.

Trying to 'fix' the converging lines in Photoshop can be done, but only in a limited amount! They 'stretching' of the pixels to widen the narrow part out will cause very visible pixel distortions when they are stretched too much!