John Paul Caponigro's "Lens Vignetting"
There are three types of vignetting -- mechanical, optical, and pixel
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 a faulty lens hood, thick or stacked filters, secondary lenses, or elements positioned within the lens designed to limit chromatic aberrations and flares. If the cause is something like the wrong lens hood or stacked filters at the front of the lens, stopping-down to a smaller aperture will make the dark edges more pronounced, and will not eliminate the vignetting.
|Optical vignetting is produced by light falloff inherent in lens design. This is the type of vignetting that concerns most photographers of today’s digital SLRs, especially since light fall-off from center to the edges is much easier to see in an on-screen digital image than it would be on a film negative. It’s a fact that all lenses will tend to transmit more light at the center of their optical axis than at the outer edges, especially at wider apertures. The amount of visible vignetting, however, will vary from one lens model to another -- 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. Some fast-aperture lenses, or wide-range zoom lenses, also tend to be more prone to visible levels of light fall-off at wide lens openings Optical vignetting can be reduced and in some cases nearly eliminated by using smaller apertures.
|Pixel vignetting only affects digital cameras and is a by-product of the physical depth of photon wells that capture light at each pixel. As the angle of light that enters a well becomes more oblique pixel vignetting increases. Even though this is a digital imaging phenomenon, it can be influenced by the lens in use. You’re more likely to experience this with wide-angle and/or wide-aperture lenses than you usually will with telephotos.
Vignetting is at its 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.)
Regardless, the cool thing is that there are various tools in today’s software to compensate for vignetting. With a few easy steps, it’s possible to minimize and in some cases eliminate it altogether.
Software adjustments for vignetting, using Canon’s Digital Photo Professional (DPP)
Whether you shoot RAW or JPEG images in your digital camera, there are software options to reduce any light fall-off you may encounter. For some Canon EOS users who shoot RAW original images, depending upon the camera and lens(es) you use, you may find all you need within Canon’s supplied Digital Photo Professional (DPP) software – version 3.2 or higher.
If one of the following cameras is used along with one of the following Canon EF or EF-S lenses, the Lens Aberration Correction function in DPP 3.2 and up will be active and available (please note that if a different camera or lens is used, the feature is disabled, and will be grayed-out on DPP’s screen).
|Canon EOS Cameras Offering Correction
|1Ds Mark III*
||1D Mark II N
|1D Mark III*
|1Ds Mark II
* Cameras that automatically put proper "Shooting Distance" on adjustable slider in DPP
|Canon Lenses Offering Correction
|EF 14mm f/2.8L**
||EF 50mm f/1.4
||EF 24-70mm f/2.8L
||EF-S 18-55mm f/3.5-5.6
|EF 14mm f/2.8L II
||EF 85mm f/1.2L**
||EF 28-70mm f/2.8L**
||EF-S 17-55mm f/2.8 IS
|EF 20mm f/2.8
||EF 85mm f/1.2L II
||EF 24-105mm f/4L IS
||EF-S 60mm f/2.8 Macro
|EF 24mm f/1.4L
||EF 17-35mm f/2.8L**
||EF 28-200mm f/3.5-5.6
||EF-S 55-250mm f/4-5.6 IS
|EF 28mm f/1.8
||EF 16-35mm f/2.8L**
||EF 28-300mm f/3.5-5.6L IS
|EF 35mm f/1.4L
||EF 16-35mm f/2.8L II
||EF 100-400mm f/4.5-5.6L IS
|EF 50mm f/ 1.2L
||EF 17-40mm f/4L
||EF-S 18-55mm f/3.5-5.6 I
** Discontinued as of May 2008
If you have RAW files taken with one of the compatible cameras and a compatible Canon EF/EF-S lens, open a RAW file in DPP and click on the EDIT IMAGE button at the top of the screen. The image will appear enlarged, in its own window. If you don’t see the toolbar at the side of this window, select View > Tool Palette to make it appear. Click on the top tab of the palette for Noise Reduction/Lens Correction (NR/Lens).
Check the box next to “Peripheral Illumination”. Canon’s engineers have measured and programmed-in the actual expected level of lens vignetting for specific Canon lenses, when used on the compatible camera bodies mentioned above. It even reads and considers the focused distance used in the particular photo you’ve got on-screen. With this one check-box, you can automatically reduce or eliminate visible vignetting. And you still have the ability to manually move the software’s sliders to further adjust vignetting control, if you desire. After you click OK, when you process this RAW file, the Peripheral Illumination adjustment is automatically applied.
As mentioned above, Canon’s built-in correction only works for RAW original files, not JPEGs, and the Lens Correction can only be used if specific cameras *and* lenses are used. For users of other equipment, or if you shoot JPEGs, there are still methods to reduce any visible vignetting, using Adobe Photoshop CS3 – either the program alone, or by using its companion RAW file processing software (Adobe Camera RAW). Adobe’s Lightroom software likewise offers tools to accomplish this.
Please note that there may be other third-party software programs from other manufacturers that may let you accomplish the same or similar tasks as those described here.
Software adjustments for vignetting, using Adobe® software
Adobe Photoshop CS3 has a variety of built-in Lens Correction controls. Among them are a pair of sliders to give very fine control to reduce any vignetting in your images. With Photoshop CS3, this is possible for any image, regardless of whether it’s a RAW or JPEG original.
Photoshop CS3’s corrections are in its Filter menu:
FILTER > DISTORT > LENS CORRECTION... will bring up a new window with a full tool palette. Unlike Canon’s DPP option, there’s no one-check automatic correction; you’ll have to use the sliders to determine the amount of correction needed.
However, the benefit is that once you have a specific correction in place for a given lens, lens aperture, and so on, it can be saved and then called up for future use with other images, shot at the same settings with that same lens.
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 PresetsSave 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.
You can test how much vignetting a lens produces and create standard corrections for images produced with it with Adobe’s Photoshop CS3, Adobe Camera RAW, or Adobe Lightroom software.
Find a suitable test subject. It must be light colored, and uniform in tone. An ideal starting point is the clear NORTH sky, on a sunny day. Other possibilities include flat light-colored walls, and even uniform pieces of paper will do. Uniform fields with little or not texture are ideal. Imaging Expo’s® ExpoDisc and similar products that attach to the front of the lens can be useful for testing vignetting; as well as white balance, noise, and dust adjustment.
Test the variables. Make a number of exposures at various apertures. Start with your widest aperture, and work your way down, in full-stop aperture increments. If you are using a zoom lens, make these test exposures at various focal lengths and at the same range of 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 ( as described above).
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 variation from one lens model to another.
John Paul Caponigro is an internationally respected fine artist, a member of the Photoshop Hall of Fame, author of Adobe Photoshop Masterclass, the DVD series R/Evolution, and a renowned Canon Explorer of Light. Learn more about him and his work at The Canon Digital Learning Center, or at www.johnpaulcaponigro.com
The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.
All images are copyright JP caponigro, Rudy Winston