I’ve just realised that I hid away a very useful tip in a rather long post the other day, one which its taken me rather a long time to realise. Which is:
With ultra wide-angle lenses, correcting distortion isn’t necessarily a good idea.
In particular, Lightroom’s default settings with the 10.5mm Nikon fisheye are quite unusable, and images taken at or near 16mm with the 16-35mm are often less pleasant.
The default profile with both lenses sets distortion correction to 100, but except in some special cases its best to set the default to 0.
Lightroom (and presumably ACR) lets you easily change the default. Here’s how to do it:
1. Go to the Lens Correction Panel, select the profile tab,
2. Make sure you have Enable Profile Corrections checked and the correct lens profile displayed.
3. Make the change you want – usually setting Distortion to zero.
4. Under the Enable Profile Correction line is the Setup, which will now be ‘Custom’.
5. Use the triangles to the right of ‘Custom’ to select ‘Save New Lens Profile Defaults.
The 10.5mm fisheye lens actually has very little distortion – but it has a fisheye perspective (I think an equisolid angle projection), enabling it to have a pretty huge angle of view – around 180 degrees across the image diagonal and around 145 degrees horizontal. The profile assumes it ought to be rectilinear, and this really just isn’t possible for such a wide angle of view. Only about half the image is usable, and it simply negates the idea of using the lens. You may occasionally want to use just a little distortion correction – perhaps a value of 20 or 30, but generally its far better to leave it to zero. If you want at less ‘fishy’ result, try a plugin like Fisheye Hemi, which renders the verticals straight (though if the lens wasn’t level they will converge or diverge.) PT Lens will also ‘de-fish’ images but in a different manner which loses a little more of the image, or you could play with the free Hugin panoramic software. PTGui is rather more expensive and works very well too, giving a choice of projections and if you want to make panoramas is the software I’d recommend for that.
At 16mm the 16-35 has very noticeable barrel distortion. But it’s only really noticeable on buildings and similar subjects. But what we do get noticeably in any very wide angle rectilinear lens is a distortion that increases towards the edges and corners of the frame. It’s generally most noticeable in circular or spherical objects and you can easily see it by viewing a ball through the camera and moving the camera to put it in the centre and then the edges and corners of the frame. If you think of the circular object producing a circular ray of light that will look circular if it hits the sensor at right angles, but as you move it away from the centre of the image, the light ray is hitting the sensor at a more oblique angle, producing this ‘distortion’.
Barrel distortion actually makes this effect less obvious, stretching out the subject in the middle of the frame and compressing the edges. The 4% or so distortion the designers allowed in the Nikon is actually remarkably effective when applied to roughly spherical objects like heads, making them look more natural, and the little increase in size in the centre brings out that part of the image, making it seem closer – and the main subject of the picture is often fairly close to the centre.
It’s a distortion that I suspect Mr Nikon (or whoever designs their lenses) may well have deliberately allowed or even encouraged at the very wide end, knowing both that it would enhance many images, but also that because of its uniform nature it can easily be removed for subjects where accurate drawing becomes essential.
By the time the lens is at 21mm, distortion in the lens is generally pretty low, and at 24mm roughly zero, with a little pincushion distortion above that, seldom enough to be noticeable except in the most critical images.
Correction of distortion always comes with some loss of sharpness, though only generally noticeable at a pixel peeping level. It is seldom necessary to correct distortion for this lens, unless you are an architectural photographer, and for most of us the best default will be to set distortion to 0 and save this as the new default for the lens.