Tokina FíRIN 20mm f/2 FE AF - Review / Test Report - Analysis
Lens Reviews - Sony Alpha (Full Format)

Distortion

Prime lenses tend to produce minimal image distortions and that applies to the Tokina FíRIN 20mm f/2 FE AF as well - mostly at least. Technically the distortions are very low but there's a wavy sub-frequency. That being said things are perfectly straightened out with image auto-correction.

Vignetting

Tokina shares a weakness with most fast lenses - high vignetting at maximum aperture. At around 3EV (f-stops) the light falloff is very obvious at f/2. Stopping down reduces the issue but it remains visible unless you activate image auto-correction. In this case, the vignetting is acceptable at f/2 (1.5EV) and mostly gone from f/2.8 onward.

MTF (resolution)

The Tokina FíRIN 20mm f/2 FE AF does a fine job in terms of resolution albeit it's not perfect - which is hardly surprising given the fast ultra-wide character. The most stunning aspect is the excessive sharpness in the wider center zone of the image field. The results are pretty much perfect here and between f/2 and f/5.6, the lens is surely capable of outperforming the 42-megapixel sensor of the test camera in this zone. The quality drops towards the borders/corners, of course, with f/2 as a weak spot. The borders are still Okay at this setting but the corners are soft. Stopping down to f/2.8 helps but better choose at least f/4 for good results. The sweet spot of the lens is reached between f/5.6 and f/8 with very good to excellent borders and very good corners. f/11 remains perfectly usable. Beyond diffraction has a more significant impact.

The field curvature is minimal. The centering quality of the tested sample was good.

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)

On Sony cameras, you don't really have to worry about chromatic aberrations due to image auto-correction. However, if you prefer to disable this, the CAs remain below disturbing limits. Please note, however, that color blooming effects can be seen in extreme contrast transitions at f/2.

Bokeh

Wide-angle lenses tend to have a very rough rendition of out-of-focus areas. While we haven't "formally" tested the aspect, the field results indicate that the Tokina FíRIN 20mm f/2 FE AF is better that most lenses in this class. Edge-transitions are pretty smooth, for instance. Below are two sample images taken at f/2 (also available in full-size format on the next page).

Stars & Flare

Another aspect sometimes asked by readers is whether a lens can produce star effects with strong light sources. The image below was taken at f/11 and, as you can see, the sun is showing rays indeed.

The image is also showing some flare effects. Now please note that there is no lens which is free of flare and glare. You can pretty much always find an angle where strong frontal or stray-light produces side effects. The Tokina produces some greenish blobs here which is not real but this is still better than rainbow colors that we have seen elsewhere.