Previous page Next page

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.

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 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 5D Mark II you can expect fairly strong corner shading when shooting wide open, though how much varies considerably from lens to lens (the EF 16-35mm F2.8 L II USM, for example, has some shading at 16mm even at F11). Unsurprisingly the 5D Mark II has almost identical fall-off characteristics as the original EOS 5D. Thumbnails from other lenses are included further down the page.

Whether light falloff is a problem will depend on the scene being shot and also user preference. In most cases the 'problem' can be corrected quite easily in software, but in the most extreme cases (such as shooting the EF 24-105mm F4 L IS USM wide open at the 24mm end) the vignetting is not possible to fix completely even with the Vignetting slider set to full in ACR. This is especially evident in situations where there is a lot of blue sky or shooting into strong light sources (although to be fair Canon's own DPP software can fix these cases near-perfectly).

Lens: EF Canon 24-70mm F2.8 L USM

Canon EF 24-70mm F2.8L USM fall off thumbnails

 
@ 24mm
@ 70mm
F2.8
F3.5
F4.5
F5.6
F7.1
F10

Canon EF 50mm F1.4 USM Fall off thumbnails (F1.4-F2.5)

F1.4 F1.6
F1.8 F2.0
F2.2 F2.5

Canon EF 16-35mm F2.8 L II USM Fall off thumbnails

 
@ 16mm
@ 35mm
F2.8
F3.5
F4.5
F5.6
F7.1
F10

Canon EF 24-105mm F4 L IS USM peripheral illumination correction

The 5D Mark II features Canon's new peripheral illumination correction, first seen on the EOS 50D. This uses falloff profiles specific to each lens design, and therefore won't work with third-party lenses. Since the EF 24-105mm F4 L IS is included in a kit with the 5D Mark II, it is useful to test the effectiveness of the new feature with this lens. The default setting for peripheral illumination correct is Enable. The thumbnails below show that the in-camera correction appears to work very well.

First at the 24mm end:

 
OFF
ON
F4.0
F5.6
F8.0
F11
F16

And at the 105mm end:

 
OFF
ON
F4.0
F5.6
F8.0
F11
F16
Previous page Next page
1390
I own it
161
I want it
426
I had it
Discuss in the forums

Comments

reanim888

As I know when the original 5D debuted three years ago, it wasn't clear why most enthusiasts would want such a camera. Though it captured excellent, high resolution images, it was slower and bigger and more expensive. Today the market has changed significantly, and it's clear that the market is ready for full-frame digital SLRs that can turn out high image quality. High quality is one thing, but being a camera that can deliver high quality over a wide range of lighting conditions and different ISO settings is what makes the Canon 5D Mark II such a compelling choice, and a clear Dave's Picks.
It's really very very good.

1 upvote