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Vignetting & Light Falloff

Vignetting and light falloff aren't something we would normally test in our digital SLR reviews, primarily because cropped sensor digital SLR's and don't exhibit much falloff. With full frame sensors, however, there's a far more real risk of corner shadowing (especially with wider lenses), though it's unusual for it to be an issue in everyday photography.

Technically vignetting refers to a darkening of the corners of the frame due to a physical obstruction such as the rim of the lens barrel or a filter, light falloff refers to a reduction in the amount of light reaching the far corners of the frame due to the angle of incidence of the light reaching there. Light falloff is sometimes referred to as cos4 vignetting. In this section of the review we will refer to this effect as falloff for simplicity (and more likely accuracy) however it could well be either or both vignetting / light falloff.

Since the v1.1 firmware upgrade the D3 has offered a fairly effective four level Vignetting Correction option (Off, Low, Normal, High) which uses masking to brighten up the corners of JPEGs in-camera. This functionality has also been added to the latest version of CaptureNX. For more information and to see the results of each setting see the section at the bottom of this page.

Testing


Measurement Areas
We aim the camera at a white wall (about 0.5 m away) which is evenly lit by two soft boxes (producing about 10 EV across the entire wall), and a heavy diffuser placed over the front of the lens. A sequence of shots are now taken at every aperture from maximum to F11 (beyond this there's only a very slow roll-off from the lens & camera combinations we tested) with a variety of lenses.

These images are then processed by our own analysis software which derives an average luminance (Lum) for the four corners of the frame (5% each) as well as the center (10%), the corners are averaged and the difference between this and the center of the frame is recorded. This value can then be plotted (see graphs below) as a representation of the approximate amount of falloff.

Hence falloff of -30% would mean that if the luminance center of the frame was at exactly 100% (pure white) the average luminance of the corners would be 70%. Anything more than -20% may well be visible in everyday shots, although this depends on the framing of the shot and the exposure.

Range of falloff

The chart below demonstrates the difference that these figures above can make, we took the blank wall luminance value of 75 (about 190,190,190 RGB) as our normal level. Remember that these patches are solid and the actual effect of shading is a softer gradual roll-off which would never be so obvious. The thumbnails are created by breaking the fall off into the same bands for clarity, so the same comment applies to them.

Fall off results

As you can see with wide zoom lenses on the D3 you can expect fairly strong corner shading when shooting wide open, though how much varies considerably from lens to lens; some zooms are better in this respect (the 28-70mm F2.8 is far better than the compact 24-85mm, for example). With decent quality optics the effect is minimal once close the aperture down a couple of stops (once you get past F5.6 you'll struggle to see the shadowing in most shots).

Although you can see fall off in some shots with some lenses, whether or not it's seen as a 'problem' (one that's common to all larger format sensors) will vary from user to user. It's easy to remove (and can now be fairly effectively removed in-camera), and in most situations simply won't be an issue.

Lenses: AF-S 14-24mm F2.8 G, 28-70mm F2.8 D and 24-85mm F3.5-4.5 G

AF-S Nikkor 14-24mm F2.8 G ED fall off thumbnails

 
@ 14mm
@ 24mm
F2.8
F3.5
F4.5
F5.6
F6.3

AF-S Nikkor 24-85mm F3.5-4.5 G Fall off thumbnails

 
@ 24mm
@ 85mm
F3.5  
F4.5
F5.6
F8
F11

Vignetting Correction

As mentioned above just before this review was published Nikon announced a firmware upgrade for the D3, one of the key features of which is a new (and rather rudimentary) 'Vignetting Control' option in the Shooting menu. The new menu offers four levels of vignetting control (Off, Low, Normal and High) and is applied to camera TIFFs and JPEGs (an update to Capture NX offers a vignetting control slider with a -100 to +200 range that is similar to the tool in Adobe Camera Raw).

What's not clear from either the documentation offered by Nikon or the results below is whether the correction applied in-camera is in any way tailored to the characteristics of the lens in use (i.e. whether the camera contains profiles for individual lenses) it would appear not to be. As the graphs and thumbnail graphics below show it would appear that the amount of correction applied is pretty regular. We also tried a variety of lenses at different focal lengths and different apertures and loaded the RAW files into CaptureNX with Vignetting Correction set to 'High' (RAW files are tagged with the VC setting). In every single case the result was that the Vignetting Correction slider was preset to 70%, which would seem to imply there's no lens-by-lens profiling.

There are a few lenses that aren't compatible with the new feature (the 14mm f2.8 and 16mm f2.8 fisheyes, 20-35mm f2.8 D, 24-85mm f2.8-4.0 D and all DX and PC Nikkors), though this is presumably simply because they produce way too much vignetting to safely correct using masking.

All in all , if corner shadowing is a problem for you (in most cases I actually like a bit of vignetting from an aesthetic point of view, but that's just me) then the system does a pretty good job of reducing the it, meaning you can shoot at - or near - maximum aperture on most lenses if you use the high setting.

Nikon warns in its documentation that 'Depending on the scene, shooting conditions, and type of lens, TIFF and JPEG images may exhibit unevenness or variations in peripheral brightness, while Custom Picture Controls and Nikon Picture Controls that have been modified from default settings may not produce the desired effect. Take test shots and view the results in the monitor'. So if you intend to make use of it on a regular basis we'd suggest you do some testing with your own lenses at the various settings to ascertain the optimal setting for your needs.

Lenses: AF-S 14-24mm F2.8 G, 28-70mm F2.8 D and 24-85mm F3.5-4.5 G

Vignetting Correction Settings thumbnails (14-24mm at F2.8)

 

AF-S Nikkor 14-24mm F2.8 G
@ 14mm F2.8

AF-S Nikkor 14-24mm F2.8 G
@ 14mm F2.8

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Vignetting Correction Settings thumbnails (24-85mm at maximum aperture)

 

AF-S Nikkor 24-85mm F3.5-4.5 G
@ 24mm F3.5

AF-S Nikkor 24-85mm F3.5-4.5 G
@ 85mm F4.5

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