Canon 50mm f/1.8 II
By Jim Tanner

Center Sharpness
The DxO Blur Plots and Figure 1 below display a sizeable quantity of data about the Sharpness of the Canon 50mm f/1.8 II lens itself and how it performs relative to the six lenses we included in this 50mm shoot-out. When you first see the blur plot for this lens, the extreme softness of the corners at f/1.8 and f/2 is very eye-catching. But the soft corners are exaggerated by the center frame sharpness which according Figure 1 is slightly less than 1.4 blur units, a pretty good wide-open value for any lens, much less for one that sells for about $70. Continuing with the Blur Plots, you can see the corner softness decrease (from the high value at f/1.8) at f/2; and by f/2.8, the severe softness is gone. At f/4 and beyond, each Blur plot is relatively flat and remains quite sharp until f/16 when early diffraction effects (which are, of course, even greater at f/22) set in.
Those blur plots are informative and a lots of fun!

Figure 1. Center Sharpness: Canon 50mm f/1.8 II versus Six-Lens Average

Now, more about Figure 1 which depicts (in purple) the center-frame sharpness for the Canon f/1.8 over its full aperture range. Also shown (in black) is a plot of the group average (of the six lenses employed in this review) blur value for the aperture range (f/1.2-f/45) spanned by the six lenses included in this shootout. The group average is shown at apertures where data is available from two or more lenses (f1.4-/22). Even a casual inspection shows that the Canon f/1.8 holds it own very well against the entire field! In fact, over this range the f/1.8 lens has an average blur factor of 1.26 blur units against a group average of 1.23. This is a really superb performance for the least expensive lens of the group; one whose owners have claimed its value for years.

Corner Sharpness
As we remarked earlier, the DxO Blur Plots show pretty severe corner softening for f/1.8 and f/2.

Figure 2. Corner Sharpness: Canon 50mm f/1.8 II versus Six-Lens Average

This is amplified by Figure 2, which plots curves of the Corner Sharpness measured in DxO blur units for both the Canon 50mm f/1.8 II lens and for the group average of the six lenses. The extreme corner softness for this lens at f/1.8 and f/2 is also shown here. Two points seem significant. First, the group plot also shows significant corner softness, albeit somewhat less than that of the Canon f/1.8, for f/1.8 and f/2. Second, from f/4 through f/22, the Canon f/1.8 and the group performances are essentially identical. The group average for the full aperture range (f/1.8-f/22) of the Canon f/1.8 is 2.2 blur units while the Canon f/1.8 average is 3.1 blur units.

Chromatic Aberration
The usual DxO Chromatic Aberration plot (back on the main page for this lens) shows the Maximum and Average Chromatic Aberration for the Canon 50mm f/1.8 lens over the full aperture range of the lens. There is nothing particularly noteworthy about the data, that is, there are no wild swings or particularly high values over the full spectrum.

Figure 3. Chromatic Aberration: Canon 50mm f/1.8 II versus Six-Lens Average

The two purple curves of Figure 3 depict the same data shown in the graph we just discussed, a graph that is included with each SLRgear lens review. The black curves of Figure 3 show the group maximum CA and average CA at each of the nine apertures in the f/1.8-f/22 range. It is very clear that the Canon f/1.8 does significantly better than the group. (!) The six-lens averages (max = 4.9, ave = 2.1) are about double those (max = 2.5, ave = 1.1) for the Canon f/1.8. Once again, the Canon 50mm f/1.8 II performs admirably when compared to the other lenses, all of which are more expensive.

Shading (Vignetting)
The DxO Shading (Light Falloff, Vignetting) graph indicates an initial (f/1.8) Shading slightly less than 0.4 EV which falls rapidly through the lens aperture range (f/1.8-f/22) to a fairly constant value less than 0.1 EV. There's little, if anything, unusual here.

Figure 4. Shading: Canon 50mm f/1.8 II versus Six-Lens Average

Again, the purple curve of Figure 4 repeats the graph shown on the DxO plot, with the group performance added in black. Over this range (f/1.8-f/22) the group average is 0.15 EV while the Canon f/1.8 has an average value of 0.12 EV, an insignificant difference.

Distortion
DxO Analyzer performs two measurements for distortion by a lens, the Maximum Distortion and the Average Distortion over the entire frame. The Canon 50mm f/1.8 II has values (max = 0.15%, ave = 0.07%) while the six-lens values are (max = 0.14%, ave = 0.06%). Two of the other five lenses displayed better values than these for the Canon 50mm f/1.8 II, but the distortion levels shown by the Canon 50mm f/18 are very good by any standard.

AF Operation
On the Canon 20D, the Canon 50mm f/1.8 II takes less than a second to go from infinity to closest focus (about 34 cm). It's certainly not USM and grinds a bit; even so, it focuses very efficiently. At closest focus, the width covered is about 14 cm. (That is, it's by no means a macro-focusing optic.) There is no distance scale on the lens; the manual focus ring is very narrow and a bit tedious to use; but once again, it only costs $70.

Build Quality and Handling
The lens is very light, seems fragile, and mostly plastic. But, don't forget, it is amazingly sharp in the center (with some corner sharpness wide open), does very well in its other characteristics, and only costs $70!

The Competition
The Table below summarizes the performance of the six lenses over the (f/2.8-f/16), the largest aperture range common to lenses in this shootout. In a later report, we will expand this table graphically by showing the full-aperture-range performance for each leans against each other lens for Center Sharpness, Corner Sharpness, Chromatic Aberration, and Shading. This will be a total of 60 graphs which reveal the dirty details of this intense competition.

Conclusion
This lens has received a lot of attention as one of the true bargains in the Canon lens offerings. Its f/1.8 maximum aperture is great for available-light shooting; and when you stop it down, it really delivers excellent optical performance. Wide open, this lens is sharp enough in the center, but very soft in the corners. On a subframe body, its other characteristics are surprisingly good wide open, with very low chromatic aberration, modest (about 1/3 stop) vignetting, and very low distortion (0.15%, barrel). When you stop it down, the f/1.8 does nothing but improve, and at apertures from f/2.8 through f/11 (best at f/5.6-f/8), it's flat-out excellent, very sharp from corner to corner, with very low CA, and practically no light falloff in the corners.

There's no getting around it, this is an inexpensive lens, which is immediately evident the moment you pick it up and feel its feather-light largely plastic construction. That said, it delivers surprising performance at a very reasonable price.

This is a great example of how knowing the performance characteristics and limitations of your equipment can help you work around them. Even at f/1.8, this lens is quite sharp in the center, so if you put your available-light subjects in the center of the frame, you'll get surprisingly sharp images at a very wide aperture. Likewise, those times when you need excellent sharpness across the frame for landscape or architectural shots, just stop down to f/8, and you will see performance worthy of a lens many times the cost of this one. With street prices hovering around $70, this lens is almost irresistible.