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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.

The D3X offers the same Vignetting Correction option as the D3 (with v1.1 firmware upgrade). It offers 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 Capture NX.

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. For this test we then took a sequence of shots at maximum aperture and at different Vignetting Control settings.

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.

Vignetting Correction test results

As mentioned above the D3X's Vignetting Control feature is identical to the D3's (with firmware v1.1). Vignetting Control offers four levels (Off, Low, Normal and High) and is applied to camera TIFFs and JPEGs. Capture NX2 offers a vignetting control slider with a -100 to +200 range that is similar to the tool in Adobe Camera Raw.

There are a few lenses that aren't compatible with this 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.

The D3 was the first Nikon to come with this feature and we've examined its capabilities quite extensively in our Nikon D3 review. Therefore for the purposes of this review we've tested Vignetting Control only at maximum aperture (this is where vignetting or falloff is most likely to occur) on two lenses - the Nikkor 14-24mm F2.8 and and older lens, the Nikkor 28-70mm F2.8. The results are very similar to what we saw on the D3. The system does a pretty good job of reducing corner shadowing. This means 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 and 28-70mm F2.8 D

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
@ 24mm F2.8

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Vignetting Correction Settings thumbnails (28-70mm at maximum aperture)

 

AF-S Nikkor 28-70mm F2.8
@ 28mm F2.8

AF-S Nikkor 28-70mm F2.8
@ 70mm F2.8

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