Field curvature + lens distortion in group shots

Started Aug 8, 2012 | Discussions thread
_sem_ Veteran Member • Posts: 4,983
Re: Field curvature + lens distortion in group shots

CherryO wrote:

1. What Nikon lens has the lowest field curvature and distortion between 20 and 24mm?

This is a problem of wide-angle perspective (projection), not field curvature or lens distortion.

DoF is usually thick enough with wide-angle lenses at normal apertures. If you need to shoot wide open, you can find the field curvature profile of any lens and arrange people accordingly.

Barrel distortion in fact helps heads in corners look more natural than a perfectly rectilinear lens.

2. Is there a trick that anybody knows of to reduce this effect (in situations when one can't get far enough away from the group to use a longer focal length)?

The best thing is to find a better location where you can use a normal lens.

Otherwise you can try adding some barrel distortion or a specific perspective transformation in post-processing. But mind this will be visible in any straight architectural lines in the background. Try composing so that dominant straight lines either run through the image centre or are cropped out if possible (tough in closed spaces), so that such distortions are less disturbing. Do not frame tightly so that there is space for cropping after corrections.
Regarding specific software:

  • DxO OP has a "volume anamorphosis" correction feature for this purpose

  • Fisheye Hemi plugin converts fisheye images to the Panini projection so that it only straightens the verticals (horizontals out of centre get a different twist). This often looks reasonable for wide people shots, see samples on Imagetrends website.

  • The free Hugin panorama software can convert among various projections and even estimate & correct lens distortion (provided that you make one good full pano set). It also works for perspective-converting single images (not only blended panoramas). Among others, two types of Panini projection may be used for the output. The user interface is a bit clumsy.

Mind that heavy stretching during perspective/distortion conversions may result in the loss of sharpness and weird look of busy details.

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