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By Root 1854 0

types of lens profiles can be generated: raw and non-raw lens profiles. In terms of the geometric distortion and chromatic aberration lens correction you are unlikely to see much difference between these two types. With regards to the vignette adjustment, here it does matter more which type of source files were used. In the case of raw files, the vignette estimation and removal is measured directly from the raw linear sensor data. Now, if the Lens Correction filter were able to process raw files directly this would result in more accurate lens vignette correction results. Since the Lens Correction filter is used to process rendered image files such as JPEGs and TIFFs, it is therefore better to use the nonraw file generated lens profiles, where available. It is for this reason that the Lens Correction filter dialog displays the non-raw lens correction profile by default and only shows a raw profile version if there is no non-raw profile version available on the system. The raw profile versions are therefore only available as a backup. However, if you go to the Search Criteria section and mouse down on the fly-out menu you can select the ‘Prefer Raw Profiles’ option (see Figure 10.11). When this is checked the Lens Correction filter automatically selects the raw profiles first in preference to the nonraw versions, but overall I recommend you stick to using non-raw profiles as the default option.

Adobe Lens Profile Creator

You can use the Adobe Lens Profile Creator 1.0 program to help characterize optical aberrations such as geometric distortion, lateral chromatic aberration and vignetting and build your own custom lens profiles. It is available as a free download. Go to the Lens Profiles fly-out menu and choose ‘Browse Adobe® Lens Profile Creator Online…’. This leads you to a page from where you can download the program. Basically you need to print out one of the supplied charts onto matt paper and then photograph it as described on pages 564–565.

Interpolating between lens profiles

The zoom lens characteristics will typically vary at different focal length settings. Therefore to get the best lens profiles for such lenses you may need to capture several sequences of lens profile shots at multiple focal length settings, such as at the widest, narrowest and mid focal length settings. The Adobe Lens Profile Creator program can then use the multiple lens capture images to build a more comprehensive profile for a zoom lens. You can also build lens profiles based on bracketed focusing distances. For example, this might be considered a useful thing to do with macro lenses, where you are likely to be working with a lens over a wide range of focusing distances.

Lens Correction profiles and Auto-Align

The Auto-Align feature now shares the same lens correction profiles as used by the Lens Correction filter dialog. This is why you should mostly see much improved performance in the way the Auto-Align feature is now able to stitch photos together. Adobe have also added caching support so that the Lens Correction and Auto-Align Layers dialogs will open more speedily on subsequent launches after the first time you open either dialog. You will also see improved auto-alignment for fisheye photos that have been shot in portrait mode. However, for this to work properly it is necessary that all the source images are shot using the same camera, lens, image resolution and focal length. If these above criteria are not met, then you will most likely see a warning message.

Photographing a display

Ideally the Adobe Lens Calibration chart should be photographed using a carefully balanced lighting setup, especially if you wish to accurately estimate the amount of vignetting associated with a particular lens. One option is to photograph the Lens Calibration chart directly from the computer display. Providing the display you are using is an LCD type and is evenly illuminated all over, there is no reason why you can't make effective measurements by photographing the chart in this way.

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This shows the setup I used to photograph the Adobe