Fuji X-Trans Flare / Ghosting Issue

I love Fuji X-series cameras – they have exceptionally good image quality, superb handling and they are just a lot of fun to shoot with. I have completed reviewing all Fuji X cameras that I have had during the last few months, including the X-Pro1, X-E1, X-M1 and the X100S. In short, an amazing array of cameras from Fuji. One issue that I overlooked while reviewing the cameras though, was the spotted ghosting issue caused by the X-Trans sensor in rare situations, as demonstrated below (shot with the Fuji 60mm f/2.4 Macro lens).

UPDATE: this turned out to be an issue with all mirrorless cameras that have a short flange distance. Please read this post to understand the issue in detail.

Since I am currently working on reviewing all Fuji X lenses, I had to go through each lens to test things like optical performance, chromatic aberrations, vignetting, distortion and flare / ghosting. During my flare / ghosting test, which involves photographing a scene with the sun in the frame at different apertures, I noticed a very interesting phenomenon – each lens that I used would produce spotted ghosts that looked very defined in a straight square pattern, in addition to the lens ghosts that we normally see from lenses. At first, I thought it was a lens issue. But then as I tested one lens after another, whether it was a native Fuji or a Zeiss lens, every single one of them showed the same pattern. After a couple of lenses, I realized that these patterns are not from optical characteristics of the X lenses or the types of coatings used in them, but rather internal reflections involving the X-Trans sensor.

When does it happen?

If you are wondering when you would potentially see this kind of pattern ghosting, it only happens in very rare situations, where a very bright source of light (such as sunlight) is in the frame and the lens is stopped down to f/11 and smaller apertures. At larger apertures the pattern is mixed with normal flare / ghosting and is not quite visible, but as soon as you get to f/11, the pattern shows up in most shots, depending on where the source of light is is positioned within the frame (see more on this below).

Proof that it is not lens reflections

It is normal for any lens to produce ghosting and flares when they are directed at bright sources of light. It happens due to internal reflections occurring within the lens. However, these reflections vary from one lens to another and they certainly vary by focal length. In the case of the Fuji X lenses, they each show different tolerances to ghosting and flare, but those optical characteristics are recorded separately from the pattern ghosting that I demonstrated in the very first image. Take another look at that same image and notice that the magenta / green ghosts from the lens actually show up from the center to the right of the image frame. The “rainbow” patterns surrounding the sun have nothing to do with those ghosts and those are coming from another source. Considering that the pattern is repetitive in a square box, I think that it is coming from the X-Trans sensor. Probably has to do with microlenses on the surface of the sensor that are very prone to reflections. Since the light is falling at extreme angles to the surface of the sensor when it passes through a small aperture opening, the angle of light is most likely the cause of such microlens reflections. Interestingly, this effect is minimized when the sun is in the center of the frame, as demonstrated below (shot with the Fuji 27mm f/2.8 lens at f/11):

However, the moment you move the source of light away from the center, all Fuji X-series cameras show the same problem. Here is an example of the same rainbow pattern that is seen in an image shot by the Zeiss Touit 32mm f/1.8 at the same aperture of f/11:

And here is another example from the Fuji 18-55mm f/2.8-4 OIS shot at f/16:

As you can see, this pattern appears no matter what lens is used, which shows that it has nothing to do with optical reflections.

How to reduce rainbow ghosting

Unfortunately, those of us that like to photograph sunrises and sunsets with the sun in the frame using the Fuji X series cameras will have to think of ways to reduce this problem, since there is no other way to deal with it for now. Here is a list of suggestions to reduce the effect:

1. If it is acceptable to your framing, position the source of light as close to the middle of the frame as possible – this seems to reduce the issue. However, this might not matter if the source of light is too bright, since the pattern might actually spill all over the frame.
2. Try not to photograph very bright sources of light in the first place. During sunrises and sunsets, the sun should not be very bright when it is close to the horizon, which will naturally reduce such reflections. See if there are any natural ways of partially blocking the sun (such as trees, branches or leaves). I have done it a few times and it actually works even at very small apertures, as demonstrated below:

   

3. Try not to go beyond f/8 if the rainbow pattern is noticeable at smaller apertures. If you are maxing out on the shutter speed, it is best to use a neutral density filter rather than stop down the lens.