Review by Markus Stamm, published July 2012
Introduction
Sigma offers a trio of fast wide angle lenses, featuring focal lengths of 20, 24 and 28 mm. All three lenses share a maximum aperture of f/1.8 and a very short minimum focus distance, which allows for interesting and often dramatic perspectives of close subjects.
In this review we'll have a look at how the 24mm lens performs on our current FX test camera, the Nikon D3x. Due to the similarities of the lenses, the three reviews share large portions of text.
The lens belongs to the high end line of Sigma lenses (EX) and, from the mount to the focus ring, the build quality is actually on a high level. However, the frontmost part that holds the inner lens tube wobbles quite a bit.
The broad focus ring works as a clutch to switch between AF and MF mode. When pulled towards the camera, the lens can be focused manually, while the AF still works as long as the camera remains in AF mode. This way the lens allows for FTM (full time manual focusing), a feature usually only available on Nikon AF-S or Sigma HSM lenses with ultrasonic wave drives.
Typical for many Sigma lenses the focus ring of the EX 24 rotates in "Canon" style, which is the exact opposite of how these rings work on Nikkor lenses. If you're used to the Nikon way of focusing, the Sigma lens may be a challenge for your muscle memory. In addition, you'll have to remember that the focus assist in the viewfinder assumes a Nikon lens and consequently suggest the wrong direction of focus ring movement.
As can be seen in the product shots below, the lens extends a bit when focusing towards closer distance. The front element does not rotate, so using a polarizer is easily possible.
Our review unit still featured the old crinkle finish that was typical for Sigma EX lenses for many years. However, Sigma changed the outer finish to a smoother one for the whole portfolio. You can have a look at our review of the
Sigma EX 28/1.8 to get an impression of what the current finish looks like. If you purchase the EX 24 new today, it will also feature this smoother finish, unless it has been sitting on the store's shelf for a few years already.
The lens has no built-in AF motor and relies on a drive screw operated by the camera (which makes it incompatible with entry-level DX cameras that no longer feature this screw drive). Thanks to a rather short focus path the AF works quite fast.
SpecificationsOptical construction10 elements in 9 groups including 2 aspherical elements
Number of aperture blades9
min. focus distance0.18m (max. magnification ratio 1:2.7)
Dimensions83.5x82.5mm
Weight485g
Filter size77mm (non-rotating)
Hoodpetal-shaped, bayonet mount (supplied)
Other featuresLens provides distance (D) information to the camera
Distortion
The lens shows a moderate amount of barrel distortion. This can be visible in critical shots especially with straight lines near the image borders. However, the distortion is uniform and easy to correct in post processing.
The chart above has a real-world size of about 120x80cm.
Vignetting
The Sigma lens shows a pronounced amount of light fall-off towards the corners. Wide open, the corners darken a lot. As usual stopping down reduces the issue, but even at rather small apertures there is still almost half a stop of vignetting left.
We're performing our vignetting analysis based on (uncorrected) JPEGs straight from the camera. The JPG engine of the Nikon D3x features a rather flat gradation curve, thus has a moderate contrast characteristic, resulting in comparatively low vignetting figures - the corresponding Canon figures are roughly 40% higher due to the more aggressive default contrast setting.
MTF (resolution)
The lens shows very good resolution in the image center wide open, which increases to excellent levels by stopping down to f/4.
The borders and corners are a very different story, though. The borders are just fair wide open, but recover to good resolution when stopped down to f/5.6. The extreme corners are even worse wide open, but also recover to good values from f/5.6 onwards.
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding
Imatest Explanations.
Chromatic Aberrations (CAs)
Chromatic aberrations (color shadows at harsh contrast transitions) are quite pronounced and range from 1.4 to well above 2 pixels at the image borders throughout the tested aperture range.
However, CAs can easily be corrected in software or by the camera itself (most modern Nikon DSLRs remove CAs themselves if you shoot JPGs).
Bokeh
One of the primary usage scenarios for a large aperture lens is to separate the main subject from the background. In such an image the quality of the bokeh (out-of-focus blur) is of major significance.
At large apertures, the EX 24 shows quite smooth bokeh in front of the focal plane, but some signs of nervousness behind it, especially in the transition zone.
Background highlights also look quite nervous and in addition show pronounced outlining. Towards the image borders, they are cut off at large aperture due to mechanical vignetting.
Both the general bokeh quality as well as background highlights improve in quality by stopping down. However, with a wide angle lens one needs to get quite close to the main subject to still get a significant amount of background blur. The lens' very short MFD comes handy here.
Bokeh Fringing
Bokeh fringing (non-coinciding focal planes of the various colors) is a common issue with relatively fast glass. As you can notice below, the halos have different colors - magenta (red + blue) in front the focus point and green beyond. Truly "apochromatic" lenses don't show this kind of fringing but these lenses are very rare - especially below 100mm. Unlike lateral lateral CAs, bokeh fringing cannot easily be fixed in post processing.
Typical for most fast primes, the EX 24 shows some amount of fringing at large aperture settings, which can of course be reduced by stopping down.
Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/1.8f/2.8f/4.0f/5.6f/8.0Sample Shots
The following sample shots were taken with a D3x and RAW-converted via CaptureOne.
Click on a thumbnail to view the original file (opens in a separate window).
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed160
Focal Length24.0mm
Aperture:f/2.8
Exposure1/6400s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed100
Focal Length24.0mm
Aperture:f/8.0
Exposure1/400s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed100
Focal Length24.0mm
Aperture:f/8.0
Exposure1/200s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed100
Focal Length24.0mm
Aperture:f/4.5
Exposure1/500s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed100
Focal Length24.0mm
Aperture:f/3.5
Exposure1/1000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed100
Focal Length24.0mm
Aperture:f/4.5
Exposure1/800s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/4.0
Exposure1/2000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/2.5
Exposure1/5000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/2.8
Exposure1/2000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/6.3
Exposure1/640s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/5.6
Exposure1/250s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/5.0
Exposure1/1250s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/1.8
Exposure1/5000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/4.0
Exposure1/2500s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/8.0
Exposure1/800s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/6.3
Exposure1/1250s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/5.6
Exposure1/1250s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/8.0
Exposure1/1000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/7.1
Exposure1/320s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/8.0
Exposure1/200s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/1.8
Exposure1/4000s
MakeNIKON CORPORATION
ModelNIKON D3X
ISO Speed125
Focal Length24.0mm
Aperture:f/8.0
Exposure1/250s
Verdict
Just like its slightly longer sister lens, the Sigma AF 24mm f/1.8 EX DG leaves us with a mixed feelings. The center resolution of the lens is nothing to complain about, at least when stopped down, while the borders and corners disappoint especially at large apertures. Vignetting is quite pronounced wide open. CAs are a somewhat pronounced while distortion is well under control for a wide-angle lens.
The bokeh is somewhat nervous at large apertures, but improves considerably when stopped down a little.
The build quality is a bit of a negative surprise because of the wobbling inner lens tube.
So, just like the EX 28/1.8, it's not an attractive choice for landscape shooters, but because of its very short minimum focus distance it's an interesting lens to shoot close-ups with wide perspectives. Optical Quality:
to
Field Quality:
(Landscapes)
(Close-up fun)
Mechanical Quality:
(downrated due to wobbling)
Price/Performance:
What does this mean ?
