In this article, I would like to see how well my lenses distribute the gathered light over the sensor area.
I want to keep this article rather short and will spare you the dozens of images, because looking at a white wall isn’t that much fun anyways.
What is Vignetting?
Vignetting can be observed with photographic lenses of all focal lengths at all sizes and in every single prize category. Even the very expensive Leica glass and the Zeiss OTUS lenses suffer from vignetting.
Its effect is usually stronger the smaller the lenses and the larger the aperture opening, but even some comparably huge modern lenses, such as the Sigma ART 50/1.4 or the Zeiss MILVUS 50/1.4 suffer from strong vignetting.
The explanation for this effect is not so simple (see this Wiki article for more information):
The glass has to spread the light gathered evenly on the sensor area. However, with large apertures and small lens bodies (to save size and weight) there will always be some optical vignetting added to the pixel vignetting only occurring in digital cameras. The amount of natural vignetting is more common in wide-angle lenses, though.
One can easily remove vignetting in post-processing in most cases, because it’s even around the frame and most modern lenses have a camera profile in Lightroom that will correct for distortion and vignetting. (Some manufacturers won’t even let you chose whether to leave vignetting in the image or not. Yes, Fuji, I’m talking to you!)
Vignetting with portrait photography can be a desired effect, because it increases the viewers focus on the subject.
However, with landscapes, architecture and especially astrophotography vignetting is very nasty because it results in an unevenly lit image. (In the case of astrophotography this will also require you to brighten the image in the corners and thus induce more noise.)
How did I test?
I shot this comparison about 1m away from a white screen (home theatre) with a bare YN560 IV flash on either side of the camera. Because of the high gain of my screen, I had to place the flashes several metres away at minimum power and set the camera to iso 50 to prevent a washing out at f/1.4.
I “measured” the amount of vignetting using the Histogram in Lightroom. In a first step, I selected a tiny crop of the frame in the image centre (see screenshot below) and changed the exposure so that the Histogram would touch one of the vertical lines. I did this for all images shot at all apertures (adjusting the white balance every time, to get a clean border on the Histogram) and noted the exposure values in an excel sheet.
Then, in a second step, I moved that tiny crop to the top left corner of the frame (again, for all images taken), adjusted the white balance and corrected the exposure so that the Histogram would again be in the exact same spot. I noted these values in my excel sheet too and took the difference to evaluate the amount of vignetting at any measured f-stop.
In a first series, I would like to show you what the images look like with all the lenses shot wide open.
Notice that I did not correct the white balance and that some lenses display significant colour casts. The Yongnuo and the Colour-Ultron are the most neutral lenses in the line-up, as you will see in the upcoming colour-cast comparison.
Also, due to differences in aperture values, light transmission and the aforementioned colour casts, not all images appear to be of identical brightness. This has no influence on my calculations, as I handled every image individually.
Upon stopping down 1 (or 1,33) stops, the situation already looks much better for all the contenders.
Now, let’s look at my calculations, because the images – at least in my opinion – are incredibly hard to judge.
The first table shows the vignetting amounts in EV-steps (stops). I also coloured the individual numbers to provide a nicer overview.
Now, here’s the whole thing in percentages, showing you how much of the light gets lost in the image corners. (1 EV is half as bright, thus 50% and 2 EV means 2 times half the light, thus 75%)
The Fujinon (non-EBC) and the Planar T* 50/1.4 have the best results in my comparison. The Nikkor 50/1.2 Ai-S suffers from the strongest amount of vignetting wide open, but it quickly deals with this issue and delivers the best result by f/2. Unfortunately, at f/2.8 only the Fujinon and the Planar deliver great results again.
The slower lenses start at similarly bad values as the faster ones do, but they come nowhere close to the latter at f/2 and the vignetting is significantly stronger than in most (not the Rikenon, Olympus and Takumar, though) of the faster lenses by f/2.8.
By f/4, with the exception of the Tessar, you don’t have to fear vignetting with any of the lenses anymore. The Fujinon and the Planar can both be used without hesitation at f/2.8 even.
This comparison clearly shows the advantages of super-fast lenses. On one hand, they let in much more light, but on the other hand, the vignetting is noticeably better once stopped down to the same aperture values as their slower brothers.
The Fujinon, after already winning the Bokeh Balls comparison (see this article here), again shines brightly over its younger brother and all the other lenses in the field. The only one to keep up is the Planar T*.