COMPARISON OF
50 mm 1:1.8 II, 50 mm 1:1.4, and 50 mm 1:1.2 L CANON LENSES

 
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 This test aims at comparing the sharpness of 50 mm lenses currently available in the Canon range. These lenses have different relative apertures (1.8, 1.4, and 1.2) and various prices (the 50 mm f/1.2 L Series being far more costly).

From left to right: 50 mm f/1.8 Mark II, 50 mm f/1.4, and 50 mm f/1.2 Series L.

All lenses are attached to the same camera, ie. a Canon EOS 5D.

The main test consists in shooting point sources. We chose a far away row of street lights located length wise in the field of view. This will clearly show optical aberrations in a synthetic and non-subjective way. With a point source it is indeed easy to locate issues such as spherical aberration, astisgmatism, coma, mounting problems (off-centering).... The lateral and axial chromatic aberration can also be assessed but we only carried out a partial analysis because the sources selected did not have a rich spectrum (high-pressure sodium vapor lamps). Note that the response we see can be regarded as the Fourier transform, the FTM, (and conversely) but with the advantage of an intuitive 2D vision.

We chose not to rely on the AF system of the camera which is not accurate enough. Focusing is performed manually by carrying out many iterations. Focus is reached at the center of the field of view without taking into account the edges of the image.

The camera was installed on a solid tripod and we used a remote control. Images are in JPEG format with the minimum compression.

The following image shows the target field: a far away row of street lights. Three areas are partially detailed (yellow squares) at the center and on the extreme edges of the Canon 5D 24x36 sensor.

The following images show the result (100% scale) for various apertures (sometimes the measure is Not Applicable (NA) when the corresponding aperture is not available).

The 50 mm f/1.2 at an aperture of f/1.2 shows good sharpness at the centre of the field. On the edges, we can see astigmatism and a form of coma, which cannot be avoided with such a focal and aperture due to the field covered (+/- 18 mm). The f/1.2 at full aperture exhibits nearly the same behavior as the f/1.8 also at full aperture. However, careful examination shows that the f/1.2 has a slight advantage due to a better correction of field aberrations (i.e. the image contrast will be better at the edges with the f/1.2, even at its widest aperture).

The 50 mm f/1.2 used at f/1.4 compared to the 50 mm f/1.4 used at full aperture is also an interesting test. Here again the f/1.2 model is a little bit better at the edge of the image. The 50 mm f/1.2 at full aperture and at f/1.4 are not that different and only the spherical aberration at the field center is reduced (but it was already not very strong). The 50 mm f/1.2 has good image quality at full aperture for this category of lenses.

At an aperture of f/1.8 the lenses behave very differently. The 50 mm f/1.2 shows very similar performance over the whole field whereas the 50 mm f/1.4 and the 50 mm f/1.8 still have problems with this aperture.

The 50 mm f/1.8 shows a good performance for its price tag, particularly at the field center.

The 50 mm f/1.2 and the 50 mm f/1.8 are nearly identical when used at an aperture of f/2.8.

The three lenses produce identical results from f/4.

The 50 mm f/1.2 is characterized by the image quality for apertures bigger than f/1.8, which can justify its price, even if its performance are not far above the cheaper models. The manufacturing quality of the 50 mm f/1.2 is clearly superior to the other two models.

Here is a test with the Canon 50 mm f/1.2 and the Canon 24-70 mm f/2.8 L zoom lens adjusted at a focal of 50 mm.

SHARPNESS ON A STAR-FIELD IMAGE

The constellation of Orion is photographed with the Canon 50 mm f/1.2L lens attached to an EOS 350D. The original IR-cut filter is replaced by a special Baader filter for a better transmission of the hydrogen Halpha line. The unit is fixed on a simple tripod. The elementary exposure time is very short (4 seconds) to avoid the rotational movement of the Earth. The observation is made since an urban site, very polluted by the artificial light. The preprocessing, from RAW files, is standard (bias, thermal signal, division by the flat-field corresponding to the aperture, registration and addition).

Below, a global view of the field and the identification of detailed area. The zone observed in bottom left, corresponds to the limit edge of the EOS 350D detector.

Crops (at the original scale):

The image becomes very fine at f/1.8 for the center of the field (the contrast remains correct with higher aperture). At the edge of the field, moderate lateral chromatism is noticed. It should be remembered that ir-cut filter transmission curve is translated toward the red. The bleue glow is the result of the Baader filter modification (the short wavelength curve is significantly shifted toward the UV after the modification - see the transmissions curves here). It is confirmed that even in edge of field, a significant proportion of the signal is concentrated on a small surface.

DAYLIGHT SHOTS

VIGNETTING

 Photometric curves along the horizontal axis of the EOS 5D detector (from RAW files and after removing the electronic bias signal).

Sample shots...

Images USM 50 mm f/1.2 + Canon EOS 5D

50 mm f/1.2 @ f/1.2
50 mm f/1.2 @ f/1.4
50 mm f/1.2 @ f/2.0
50 mm f/1.2 @ f/5.6

50 mm f/1.2 @ f/1.2 - 400 ISO - 0.5 second. Canon EOS 5D.

Canon 50 mm f/1.2 stopped at f/1.8 + Canon EOS 350D modified Baader (extended red response) at 400 ISO.
The setup is fixed on a tripod (no equatorial mount). Stack of 30 x 4 seconds frames (2 minutes exposure). Crop of the center field.
The Barnard's loop is faintly visible.

The sharpness at the field center of the 50 mm f/1.2 is clearly demonstrated from the full aperture. The whole field shows a good quality for such an extreme aperture. These images also show that the 50 mm f/1.4 has a good quality for an attractive price tag.

To sum up, the 50 mm f/1.2 has a better image quality compared to the f/1.4 (and of course to the f/1.8). The 50 mm f/1.2 at f/1.8 is equivalent to the 50 mm f/1.4 at f/2.8 - an important consideration for some applications. Depending on the user needs and requirements, price differences may or may not be justified. For my part, I likes the 50 mm f/1.2!

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