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John Paul Caponigro Photo Tip: Test for Vignetting
By John Paul Caponigro | Education/Inspiration |
May 5, 2007
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Vignetting is
In photography, vignetting is a reduction in brightness in the periphery of an image (corners and edges). Sometimes for better, sometimes for worse, a great majority of photographs contain vingetting. Darkening the corners and edges of an image directs the viewer’s attention towards the center of the image. When it becomes pronounced it may become distracting or produce an unnatural appearance.
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| By default, no adjustment is made; 0 – 0. |
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| Amount lightens corners and edges; 100 – 0 |
There are three types of vignetting; mechanical, optical, and pixel.
Mechanical or physical vignetting occurs with light emanating from object points located off-axis are partially blocked by external objects such as lens hoods, thick or stacked filters, secondary lenses, or elements positioned within the lens designed to limit chromatic aberrations and flares. Mechanical vignetting is sensitive to aperture and can be reduced by using smaller apertures.
Optical vignetting is produced by light falloff inherent in lens design. Wide angle lenses and lenses used in rangefinder and compact cameras are more prone to vignetting than longer lenses and retrofocus lenses used in SLR cameras. Like mechanical vignetting, optical vignetting can be reduced by using smaller apertures.
Pixel vignetting only affects digital cameras and is a biproduct of the physical depth of photon wells that capture light. As the angle of light that enters a well becomes more oblique pixel vignetting increases. Most digital cameras incorporate in-camera file post-processing routines to compensate for both pixel and optical vignetting.
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| Midpoint spreads the effect towards the center; 100 – 50. |
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| Upper and lower limits apply to the effects both sliders can achieve; 100 – 100. |
Vignetting is at it’s worst when lenses are focused at infinity. At close focus the field of view decreases and the image circle increases. The vignetted area is pushed outwards with the image circle and when the focus is close enough the optical or mechanical vignetting will be outside the frame. (Optical vignetting determines the size of the image circle.)
How to adjust vignetting with RAW converters
You can easily adjust the amount of vignetting an image contains in Adobe Photoshop, Adobe Camera RAW, or Adobe Lightroom.
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| When removing vignetting, the sliders can be used to produce the most uniform appearance. |
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| Save Settings in Photoshop for future use. |
To get the best results using Lens Vignetting adjustments you need to strike an optimum balance between the Amount (lightens corners and edges) and Midpoint (spreads the effect towards center) sliders. If Amount is set to 0, Midpoint will become inactive; no correction is made. Drag the Amount slider to the right to lighten and to the left to darken. The Midpoint slider let’s you control how much that adjustment spreads towards the center of the image; 100 targets the corners aggressively, while 0 extends the adjustment well into the center of the image.
Classically, when removing vignetting, the sliders are used to produce the most uniform appearance. Target the corners and edges. Avoid producing visible circles inside the edges.
With RAW converters, there are upper and lower limits you cannot exceed and the shape of the effect is fixed. You can exceed the limits of RAW converters and adjust the shape of the effect using Adobe Photoshop. These adjustments can be either in addition to or in lieu of RAW converter adjustments.
You can save custom settings for future use. In ACR 3 go to the Presets tab and use the submenu to select Save Settings. In the Save Settings window use the drop down menu to change All Settings to Lens Corrections and uncheck Chromatic Aberration. Give each setting an appropriate title. Within each tab you can load a custom setting or you can recall a settings in the Presets tab.
Vignetting Tests
You can test how much vignetting a lens produces and create standard corrections for images produced with it.
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| Presets in Lightroom can be save for future recall. |
Find a suitable test subject. Images that are more uniform in appearance display vignetting more readily than others. Large expanses of sky, flat walls, and even uniform pieces of paper will do. Uniform fields with little or not texture are ideal. Imaging Expo’s ExpoDisc can be useful for testing vingetting; as well as white balance, noise, and dust adjustment.
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| Specific fields can be saved and later combined with other saved presets. |
Test the variables. Make a number of exposures at various apertures. If you are using a zoom lens, make a number of exposures at various focal lengths and apertures. At a minimum, make tests when focused at infinity, when vignetting is at its greatest; you may also want to test the effect of significantly closer focus to see how much it is reduced.
Open the images in your RAW converter. Make appropriate compensations. Save those settings appropriately labeled for future use.
Once you have established standard corrections for lenses at specific apertures you can use saved settings to automate correction or as a baseline to begin further adjustment from.
Your settings may be good starting points for corrections for other lenses and cameras of similar types, but expect to make some minor compensations as there is always some unit to unit variation.
John Paul Caponigro is an internationally respected fine artist, author of Adobe Photoshop Master Class, and a member of the Photoshop Hall of Fame.
Get over 50 free PDFs and test files with your free subscription to "Insights" at www.johnpaulcaponigro.com.
Let us know if you found this article useful, and tell us what kinds of articles you'd like to see in upcoming issues. Send your comments and ideas to Lynne Eodice.
© Copyright 2008 by PHOTOWORKSHOP.COM
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Last Updated: Jul 3rd, 2009 - 15:04:15
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