Studio Tests - 35mm full frame
The EF 50mm F1.8 II performs much like any other 'fast 50' on full frame, with pronounced softness across much of the image area at large apertures, but giving truly excellent results on stopping down. It's not quite as good as the EF 50mm F1.4 USM when compared like-for-like (central sharpness is similar but the corners slightly softer), however it's very close indeed.
|Sharpness||The 50mm F1.8 is sharp in the centre even at F1.8, but the corners (and much of the rest of the frame) are very soft. Corners sharpen up progressively on stopping down, and by F5.6 look very good indeed. The very best performance is at F8, where this sub-$100 lens produces truly superb results right across the frame.|
|Chromatic Aberration||Lateral CA is extremely low, and even on the EOS-1Ds Mark III there's no visible fringing. There's also only a very slight level of colour blur due to spherical aberration - overall nothing of any real-world consequence.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. The 50mm F1.8 II behaves much like any similar lens on full-frame; there's significant vignetting (2.7 stops) wide open, but this disappears progressively on stopping down and is insignificant by F3.5.|
|Distortion||Distortion on full frame is about 1.2% barrel; just a hair less than the 50mm F1.4 USM, and potentially visible in the occasional shot with straight lines right across the frame (although scarcely problematic, and easy enough to fix in software).|
Full-frame compared to APS-C
Eagle-eyed viewers will no doubt have noticed that the MTF50 sharpness data at any particular focal length/aperture combination is distinctly higher on full-frame when compared to APS-C. This may at first sight appear unexpected, but in fact is an inevitable consequence of our presentation of the sharpness data in terms of line pairs per picture height (and thus independent of format size).
Quite simply, at any given focal length and aperture, the lens will have a fixed MTF50 profile when expressed in terms of line pairs per millimeter. In order to convert to lp/ph, we have to multiply by the sensor height (in mm); as the full-frame sensor is 1.6x larger, MTF50 should therefore be 1.6x higher.
In practice this is an oversimplification; our tests measure system MTF rather than purely lens MTF, and at higher frequencies the camera's anti-aliasing filter will have a significant effect in attenuating the measured MTF50. In addition, our testing procedure involves shooting a chart of fixed size, which therefore requires a closer shooting distance on full frame, and this will also have some influence on the MTF50 data.
Specific image quality issues
As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. We used the lens on both APS-C and full-frame bodies, namely the EOS 450D and the EOS 5D.
As we've come to expect from large maximum aperture lenses, flare can sometimes be an issue with the 50mm F1.8 II. With it's deeply recessed front element, the lens effectively has a permanently attached hood, and so is generally resistant to veiling flare from light impinging the front element at an angle. However the moment you point the camera towards the sun things can start to go wrong, although on the whole the lens generally seems to fare a bit better than its F1.4 big brother in this regard.
With the sun in the corner of the frame, the lens is showing large, bright red flare patterns in the opposite corner when shot at wide apertures. Stopping down progressively reduces these in size, but halation patterns around the sun increase instead; overall the best results are achieved at intermediate apertures around F5.6-F8. However to be fair the lens regains its poise very quickly as the light source is moved further off-axis, and is generally resistant to flare problems in normal shooting situations.
|F2.0, Canon EOS 5D||F5.6, Canon EOS 5D|
|F22, Canon EOS 5D||F4.5, Canon EOS 5D (sun out of frame)|
Background Blur ('bokeh'): lots of little pentagons
One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. The 50mm F1.8 can produce substantially blurred backgrounds at wide apertures, a huge advantage for portrait shooting especially on APS-C.
Unfortunately though, the character of the background blur is not tremendously attractive. This is substantially due to the lens's diaphragm construction, which uses just five blades with totally straight edges (most modern designs use curved blades). This means that the moment the lens is stopped down, point highlights are rendered as pentagons, often resulting in a remarkably distracting rendition of backgrounds that resembles nothing more than a primary-school attempt at tessellation. And things aren't so much better at F1.8; while the apertures is at least round, highlights are rendered bright-edged and harsh. Overall it's a pity Canon didn't implement a slightly more complex diaphragm construction with seven or eight blades, as this behaviour somewhat spoils the performance of an otherwise extremely fine lens.
|F4.5, Canon EOS 450D||F2.8, Canon EOS 5D|
|50% crop, lower right||50% crop, top centre|
Lateral chromatic aberration is negligible in our studio tests, and is equally near-impossible to find in real-world shots; quite simply it's not an issue when using this lens. However some bokeh chromatic aberration can occasionally be visible at F1.8-F2.2; in the example below there's a little green and magenta fringing, but the overall harshness of rendition is more visually objectionable than the CA.
|F2.2, Canon EOS 5D||100% crop|
Optical performance at wide apertures
Our studio tests show that this lens is not at its best at wide apertures on full-frame; central resolution is just fine, but the corners are extremely soft and subject to significant darkening through vignetting. However in this regard it's also important to appreciate that with the extremely small depth of field afforded by a 50mm F1.8 lens, and assuming a reasonably centrally-placed subject, the likelihood of any object in the corners of the frame being remotely in focus is in fact minimal, and corner resolution therefore near-irrelevant.
The images below illustrate the lens's performance for those inclined to shoot flat subjects at wide apertures, here using the 13Mp EOS 5D (this is admittedly not the most aesthetic of test subjects, but about as interesting as you'll get when looking for soft corners wide open on this type of lens). Contrast is clearly a bit low at F1.8, and the corners suffer from a combination of low contrast and significant vignetting (although the actual resolution of fine detail isn't too bad). Stop down to F4, and much as we saw on APS-C, the lens produces perfectly good results from centre to corner.
|Canon EOS 5D||Canon EOS 5D|
|100% crop, centre||100% crop, centre|
|100% crop, top right corner||100% crop, top left corner|