Photoclub Alpha

I have made a simple (f/2.8 and f/8 chart set) Adobe Lens Profile for the 16mm f/2.8 NEX E-series pancake lens. It seems to work well for closer distances, because that’s how it had to be made; CA is reasonably well corrected, vignetting is eliminated, and distortion of closer lines – maybe if you are looking through a door frame, etc – is very accurate. The profile was created using NEX-5 and 16mm.

You can get this profile here:

http://www.photoclubalpha.com/Sony NEX-5 (Sony E 16mm F2.8) – RAW.lcp

Right click to download/save the target file, and install this in:

Library>Application Support>Adobe>Camera Raw>Lens Profiles>Sony

Uncorrected 16mm shot

Using Adobe Camera Raw 6.2 RC with the profile active at default settings

JPEG profile added (17/08/10)

I have now added a JPEG profile from the same set of images as the raw – this is lucky, I didn’t think people would need a JPEG profile but happened to have the camera set to RAW+JPEG when the test shots were made, and this has been requested for those using HDR or other JPEG-only modes.

http://www.photoclubalpha.com/NEX-5 16mm JPEG.lcp

Above: HDR three-shot with 16mm, straight JPEG

HDR shot opened in Camera Raw without adjustments, but with the Profile enabled

Using the profiles

A full Adobe Profile is undertaken at several focus distances, apertures and zoom settings (or for prime lenses, just at a range of distances and apertures). The largest chart I can print is A2+ using the Epson 3800, and with a 24mm equivalent lens, this means having the camera surprisingly close to the target. The profile is therefore only 100% correct for subjects at 115cm from the camera, which corresponds to the 4X minimum focus distance suggested by Adobe.

I have found from using the 16mm that its optimum aperture for central sharpness is probably f/5.6, and that chromatic aberration and vignetting do not improve at stops smaller than f/8. There is a slight improvement in detail sharpness in the extreme corners at f/11 and f/16, but this is due to extra depth of field helping to cover a curved focus field. I therefore made test sets at f/2.8 and f/8 for this profile.

The geometric distortion is most visible with closer subjects such as the subject above (The Slave Girl, a bronze c. 1870 by John Bell, at Cragside House in Northumberland). This is a hand-held exposure of 1/4 at f/8, and is perfectly sharp despite the lack of stabilisation; every word of the interpretation can be read at 100%. I have found most shots are perfectly sharp with the 16mm given reasonable care, as you would take with a Leica, to breathe correctly and make a shake-free exposure. This is not the case with SLRs where the mirror action nearly always causes shake.

For more distant subjects, the 100% default setting of the ACR/LR Lens Correction panel can be reduced and where there are few straight lens removed entirely to secure the maximum field of view. Similarly, the vignetting correction can be reduced or removed entirely as the natural darkening towards the corners with this lens is attractive.

Although this profile is named to match perfectly the naming convention used by Adobe for the 18-55mm, I find that ACR 6.2 can not be relied on to use it for Auto as a default (if you work with more than one lens, Adobe Lens Correction soon proves unpredictable in this anyway). If you select Auto, then select Sony, the lens profile will be selected but the Auto button changes to Custom. If you then save new Lens Correction Defaults, or Camera Raw Defaults, ACR will attempt to force this profile on the 18-55mm and the reverse will also happen. So it’s necessary to check which profile is selected. Using ‘Previous Conversion’ for shots taken on the same lens is a quick way to get there.

The additional Manual Controls can be used on top of the profile (the second tab of the interface). The most useful are the geometric distortion (camera angle) corrections. The Chromatic Aberration/Colour Fringe controls can be fine tuned as the correction for CA while very effective relates only to the tested focus distance. CA may change with focus but my particular lens doesn’t seem to suffer from this. All that is necessary is to enable Defringe All edges as a default, and this will remove any hint of colour remaining. As a tip, setting Colour Noise Reduction to a high value can help remove CA and purple fringes in many shots processed through ACR/LR. The colour NR detects 1-2 pixel fringes just the same way it detects individual pixels, and neutralises much as it does noise.

- David Kilpatrick

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