End Colour Fringing

The Nikon digital 10.5mm semi-fisheye is one of my favourite lenses, although it needs to be used sparingly. I wrote about it at some length for About.com shortly after getting it, with various suggestions for using and altering the images it gives. Since then I’ve used it to create several images I feel proud of, subjects that just fitted the effect it gives, like this circle of druids at the spring equinox in London:

Druids in London (C) 2007, Peter Marshall
Spring Equinox at Tower Hill, 2007

Anyone reading this in Hungary who saw the recent ‘Europe of Culture – the culture of urbanity‘ show this year will have seen this picture I took at Contretype in Brussels, where the circular stairway of the Hotel Hannon provided another ideal subject.

Hotel Hannon (C) 2005, Peter Marshall

But the lens does have one severe problem, chromatic aberration, which needs to be corrected at least for good large prints. For the Hungary show, I spent ages working on the file, removing some of the more noticeable colour fringing using Photoshop.

But of course there are easier ways, and one of the best I’ve found is in Lightroom, which I now use for converting my RAW digital files. (People tell me the Nikon software does a good job, but even several years and 2 camera bodies later I still can’t bring myself to pay for the software that Nikon really should have supplied free with the cameras.) It isn’t just useful for the 10.5 Nikkor, but almost all the images I take when I want to make critical large prints, as nearly all zoom lenses show some chromatic aberration at most focal lengths (the Nikon 18-200, for example, is fine at 24mm, but away from this needs a little help.)

If there is anyone using Lightroom who has yet to find this, or anyone still wondering if Lightroom is worth the money, in the Development mode there is a panel headed ‘Lens Corrections‘ with two and a half sections. The first part has two sliders to control chromatic aberration, one for Red/Cyan and the other for Blue/Yellow. Here is a small section of an image taken by the 10.5mm, from close to a corner and at three times actual size to show the effect exagerated.

3:1 section of original
Before any correction – image at 3 times actual size

And here it is after adding -46 Red/Cyan and +32 Blue/Yellow

After Chromatic removal

There is still some colour fringing, although it is a lot improved. Below the two sliders is a ‘Defringe’ setting that controls the removal of blue fringing found in many digital images. If set to ‘All edges’ it finishes the job, giving an almost perfect result (and with a little tweaking of the sliders I could probably improve it slightly.) It actually makes the settings for chromatic aberration easier to determine if you set the ‘defringing’ first.

Image defringed

Lightroom will also do a little more for these images. Most pictures taken with the 10.5mm show some vignetting, usually giving images that are lighter at the corners. The lower half of the ‘Lens Corrections’ panel can deal with this, often looking best with values around -35 for amount and 21 for midpoint.

I spent some time playing with this today as I used the semi-fisheye for some pictures at Notting Hill Carnival over the weekend, which I’ll write about a little more later. Again it let me take pictures that could not have been taken any other way.

Peter Marshall

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