Bright light that shines directly through from the front or side is an unavoidable situation that every photographer faces from time to time, whether it is at sunset, dusk or night, or a strong spotlight used for indoor shots. Under such extreme conditions, ghosting of the light source often appears, which becomes visible mirror-imaged to the optical axis (i.e. to the center of the image). It doesn’t look good and disturbs the overall image composition.
So when designing the Distagon T* 2,8/15, a great deal of attention was paid to preventing such light reflections as much as possible. With success, as Bertram Hönlinger from the ZEISS Customer Care Center explains: “Especially when it comes to digital cameras, as a lens manufacturer we are often faced with the problem that back reflections are emitted into the lens from the filter package in front of the image sensor, usually consisting of various low-pass filters and IR cut filters directly in front of the surface of the sensor. Depending on the radius of curvature of the individual lens surfaces, ghost images of the light source can reappear in the image field. In the design we solved this problem as follows: through a smart choice of the radii of curvature of individual lenses, these back reflections can, in most cases, be moved to the outside of the image field. During the development and prototype stage, simulations and tests revealed how the Distagon T* 2,8/15 responded to that effect and whether changes in the optical design were needed. That is the most important point for us. Other manufacturers do not place as much value on that.”
The excellent suppression of reflections by the Distagon T* 2,8/15 is clear to see with interior shots where there is strong surrounding light, for example with spotlights that shine directly into the camera, as Donat Nussbaumer was delighted to discover in his pictures of a large room in the Culture and Congress Center in Lucerne: “The bright lighting in the theater is focused on the stage and therefore also toward the place where I was located as the photographer. The light shone directly into the lens. However, with the Distagon T* 2,8/15 it was possible to capture the image without any bothersome reflections. Instead, the spotlights and the rays’ consistent, star-like form, appear as highlights in the motif in the truest sense of the word.”
Like all current ZEISS camera lenses, the Distagon T* 2,8/15 comes with the complex ZEISS T* anti-reflective coating. In addition, the edges of the lenses are treated with a special deep-black lacquer to ensure maximum dampening of reflections and stray light, which it should be added cannot always be eliminated 100% in extreme light situations.
“The intensity of the unavoidable residual reflections is therefore much lower than the brightness of the actual light source in relationship to the darkest sections of the scene,” explains Hönlinger. “The sun in the photograph below, for example, is 15 exposure steps brighter than the rest of the picture. Any reflection that could materialize, whether caused by back reflections on the lens surfaces or mechanical components in the lens, should of course not have the same brightness. It is precisely this dampening effect that we achieve through the multiple coating and sophisticated procedure to blacken the edges of the lenses. As a result, the residual reflection does not stand out so much anymore.”
Light reflections are not only a technical challenge for development engineers. They are also a practical problem for photographers having to deal with extreme lighting situations in their daily work. The outstanding reflection dampening of the Distagon T* 2,8/15 makes such work far easier, as Matt Walker can attest. “There are many San Francisco Bay Area photographers who live for low fog days at the Golden Gate Bridge. This photo captures an autumn storm front entering the bay. This was my third time using the Distagon T* 2,8/15, and my second time shooting into the sun. I was amazed at this lens's ability to handle direct sunlight. I looked at every shot taken on this morning, and not one image showed any signs of sun flare. I use ZEISS lenses for sharpness and color, but the virtual lack of sun flare on the Distagon T* 2,8/15 is a real bonus.”