Years ago, every photographer used to say that you should never backlight a portrait subject due to the way that lenses render the scene. For a long time, it was very difficult to get any sort of detail on a subject when the sun was behind them. But then things started to change. Lens technology and glass coatings became better and better which delivered more contrast in a scene and brought out more details despite the subject being backlit.
To explore why and how this change happened, we talked to Zeiss, Sigma and Tamron about how it all came about.
While the backlighting a portrait subject trend has really started to take off within the past five years, the technology to get this started has been in place since at least 1973. Zeiss shared a document with the Phoblographer entitled “From the Zeiss T-coating to multi-layer coating”
The document details how advancements in technology have cut down on reflections on glass surfaces and references how in 1817 a study was done on how reflections on glass structures decrease with their exposure to the environment.
Quite obviously, technology has evolved.
Glass Element Design, Lens Coatings and How They Work
To give a bit more backstory, the lens coatings applied to glass elements were able to cut down a bit on lens flare and detail loss, but what also really helped was UV filters and reflections were cut down with polarizers. As digital sensors became better, they were able to capture more information in the dynamic range–which also contributed to the progression of backlighting. Soon Sony, Nikon and everyone else were apparently releasing information about the coatings on the glass elements and how they’d progressed.
To divert from the coatings for a second, amongst these companies was Tamron–who only a few years ago announced new rebranding with their SP system of lenses. “Our lenses start with a very high specification.” says Pat Simonetti of Tamron. “This along with modern glass such as LD/XLD/aspherical really make a difference and eBAND and BBAR coatings play a crucial role in contrast. Pat continues to explain that what aspherical elements do is give a lens less distortion in addition to improving corner resolution power–which therefore improves contrast. Further, both the LD & XLD elements in Tamron’s lenses will reduce flare and also improves overall resolution power therefore improving the contrast.
Indeed, coatings alone can’t do this and part of it comes from the design of the lenses. In fact, the loss of contrast in backlight situations is caused by several different effects inside the lens and the camera. “One of the most important is the multiple reflection of light between all surfaces where we have a transition from air to glass or glass to air.” states Dr. Hubert Nasse, Staff Scientist over at Zeiss. “In the very old lenses (before about 1950) these surfaces had no coating, and thus a reflected beam of light was just attenuated by about 4 f-stops.” This design attributed to a large number of cemented surfaces, where one glass element is directly attached to the next neighbor by a kind of glue with similar refractive index. In fact, the only way that lenses could be made practically useful was to have a small number of air-glass interfaces.
The surface reflection was a severe limitation of lens complexity. So advancements were made not only in lens design but also with the coatings. Indeed, the reflection on the surfaces created a lot of limitations. But this changed after the application of thin layer coatings to the glass surfaces and in 1935, Carl Zeiss Jena was awarded a patent for this. “The single layer coating improved the attenuation of the surface reflection to about 6-7 f-stops.”
From what we know, these coatings have evolved over time to become better and better not only in chemical formula, but in how they’re applied. “The use of coatings on the glass elements such as the super multi layer coating help drastically.” stated Patrick Santucci, the Marketing and Technical Representative for Sigma Corporation of America for the Pacific North West. “It is quite common on Sigma lenses nowadays.” Of course, we saw this when Sigma unveiled their Global Vision lineup of products and they showed the world how much different and better lenses could be. At the same time, Zeiss had unveiled the Otus lineup–which also tried to really push the way that lens technology progressed.
Way back in the day, to improve the lens coating technology, they started to realize that a single layer coating could not minimize the surface reflection within the whole visible spectrum. 6-8 thin layers were applied which became known as the Zeiss T* coating. These layers reduce the reflection effectively within the complete visible spectrum. Today a modern multilayer coating causes an attenuation of the reflected light by 8-10 f-stops.
Further, they also help with the effects of ghosting and flares–which are more or less caused by two reflections. In fact, Dr. Nasse states that a lens with modern coating with otherwise identical design the flare level will be weaker by 12 f-stops compared to a very old lens. That makes a big, big difference.
Then there’s all the other really crazy cool things that many of us have probably never thought of. “Another cause of loss of contrast can be the scattering of light by the mechanical parts which hold the elements.” states Dr. Nasse. “The development of much deeper black, light absorbing surfaces and a more careful design of their shape helps to minimize also this contribution.” Combined with modern computer modeling of lenses, we’re able to create much better optics.
Every one has known that you should always use a lens hood. There are many benefits to this including protecting the lens, cutting down on flare and adding contrast to the scene. “Lens hood is always recommended to prevent flare because what can cause it is a point light source hitting the front of the lens and so the more you can shield the front element from this potential, the better protection you have.” states André Costantini from Tamron. “When shooting directly into a light source, as the hood isn’t doing anything to protect the front element, it is having no effect.” That should be kept in mind specifically with backlighting and that’s where the coatings and modern design comes in. But if your subject is backlit and the light is a bit off to the side, then you’re a bit better off.
The following words are from Dr. Nasse at Zeiss:
“The main purpose of the lens hood, besides from some mechanical protection, is to prevent strong light from falling to the surfaces inside the camera near the sensor window.
A well-made lens hood blocks most of the unnecessary light. Let us look to three different kinds of backlight:
1) The backlight is dominated by one very bright small light source, like the sun. And this light source is well within the field of view of the lens. Then the lens hood contributes practically nothing to flare reduction.
2) When the same strong light source is just outside of the frame, the light will certainly still go through the lens and hit the walls of the black box in the camera.
From there it is scattered into the frame window on a short way and causes a flare effect. This is prevented by the lens hood. The longer and deeper it is, the better. Sometimes even very oblique rays from a strong light source cause some light scattering from front parts of the mount or even from dust particles on the first lens surfaces. For these cases the lens hood is also helpful.
3) When backlight is not caused by a strong point light source but by a large bright area, like on a misty day, then we have a combination of the two first cases. The lens hood helps to reduce the effect of the bright areas outside the frame.”
If you’re shooting backlit portraits, here are a number of lenses that each of the companies recommend in their lineup:
Tamron 35mm f1.8 Di VC USD: This latest 35mm lens offering from Tamron is surprisingly good.
Tamron 85mm f1.8 DI VC USD: Perhaps my favorite lens that Tamron currently offers.
Sigma 50mm f1.4 Art: A favorite of many photographers and arguably one of the sharpest lenses on the market today.
Sigma 85mm f1.4 EX: A classic. Not as sharp as some modern lenses, but still excellent overall.
Sigma 50-100mm f1.8 Art: Recommended for APS-C camera owners.
Zeiss Batis 85mm f1.8: For the money, it’s tough to beat it.
Zeiss Milvus 85mm f1.4: My favorite Milvus lens.
Zeiss 135mm f2: The reason why this is recommended is because of the Apochromatic design. “What makes it ideal for that is because chromatic aberrations (axial chromatic aberations) are corrected with elements of special glass with anomalous partial dispersion.” states Nicole Balle, Marketing Manager Americas for Zeiss. “The chromatic aberrations are therefore significantly below the defined limits. Bright-dark transitions in the image, and especially highlights, are reproduced almost completely free of color artifacts.”
Zeiss Otus 85mm f1.4: The creme de la creme of 85mm lenses on the market now.