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Carl Zeiss SLR Objective Lenses:
The Lenses for Digital Video and Photography |
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The briefly flashing eyes of the hero, the crumbling asphalt of the urban street canyon in which he he'll soon vanish, the unknown being gradually appearing in the foreground. Narration through pictures is always a matter of the technique used. Details and effects, such as the look of the film or the follow focus captivate the audience and pull the observer right into the action. Amazing effects can be realized in films and photography using the SLR objective lenses made by Carl Zeiss if you capitalize on their special features and follow one or two tips.
Video or film look?
The unmistakable look of moving pictures is the result of tiny details: for example, the color fidelity that is particularly evident in the hues of skin color, the specific aesthetics of movements captured at 24 frames per second as compared to the frames of TV, and the lower depth of field which makes the cinematic presentation of objects possible.
The low depth of field is a particularly attractive design tool, but at the same time a true challenge of digital cinematography. When the surroundings are imaged out of focus, the view of the observer is automatically directed to a point of interest which the cameraman can deliberately extract from the surroundings.
For a long time, low depth of field remained a domain of 35 mm film. This is due to the laws of physics as the comparatively small sensors of digital video cameras (1/3 to 2/3 of an inch in size) do not allow for low depth of field. Consequently, 35 mm film allows a person in a room to be set apart from the furnishings by the deliberate use of low definition.
Depth of field via adapters: high effort, low-light transmission power
One way of attaining targeted blurring in digital films is the use of DOF adapters (DOF: depth of field). The best known approach to this issue was first provided by P&S-Technik (Germany) and later included in the products of Redrock (USA) and SG-Pro (England). The digital video camera captures a 35 mm intermediate image that is reproduced on a rotating ground glass screen by a high-speed camera lens. Particularly popular in this context are the purely manually-operated Canon-FD lenses and the manual Nikon lenses of the past. The moving picture thus attains a soft aesthetic appearance, a grainy look – a smooth, non-digital overall image with no hard edges. The grain of the ground-glass screen introduces blur as a result of the motion blur of the screen. In this context, the rotating speed and the type of surface must be selected carefully to ensure that the image does not appear mushy or diffuse. Since the intermediate image needs to be flipped – i.e. unreversed and upright – another optical component, the flip module, is required. The back focus – i.e. focusing onto the imaging surface of the screen – must be set and fixed with high precision by the filmmaker to ensure that the images do not blurred.
This procedure also generates the desired depth of field in digital films. One crucial drawback is that the complex set-up leads to a loss of light intensity equivalent to up to three aperture stop settings. Considering that HD video cameras already have difficulties in low light conditions, this is a further shortcoming.
Depth of field without tricks: the full-format sensor is key
The Canon EOS-5D Mark II is the first camera to enable cinematographic depth of field without additional loss of light intensity, a feature that makes it truly useful for professional film-making. The most interesting feature of the EOS-5D-Mark II to the video photographer is optical imaging onto a full-format sensor with the same geometric dimensions as 35 mm analog film. The recording is in full HD: progressive 1080p. The camera initially utilized some kind of semiautomatic system which made it quite difficult to manually set the aperture stop. This was impractical for professional use, but this handicap was remedied with the release of the eagerly awaited firmware update 1.1 in June 2009. Aperture stop, ISO sensitivity and exposure time can now be set independently of each other in the manual mode. For filmmaking, the camera features sensational low light behavior. Even at night, exposures can be taken without any significant noise – provided you have a high-speed lens. One drawback is that the camera only offers a fixed frame rate of 30 fps, making users anticipate the next firmware update that will accommodate the frame rate of 25 fps in Europe.
Fixed focal length or zoom? Dedicated objective lenses for video-photography
Fixed focal length lenses have tremendous advantages over zoom lenses – especially in digital videography. Their speed is at least twice as high: the Canon EOS 5D Mark II excels through its superior low light behavior. It is therefore self-evident that only the fastest lenses, i.e. 1.4 - 1.2, should be used with the unit because even the most sensitive sensor is useless if too little light passes through the lens.
Working in full HD, you need to have razor-sharp images. Fixed focal length lenses produce much sharper images than zoom lenses and tend to exhibit less distortion at the periphery. This applies, in particular, to the Zeiss T* lenses. Moreover, fixed focal length lenses tend to exhibit substantially less "pumping" than zoom lenses. Pumping is observed when the geometry of the object appears to change while focusing. However, only the sharpness should shift while focussing, not the dimension of the image recorded.
Common and important fixed focus lengths:
The most important fixed focal lengths are 50 mm (the normal lens), 28 mm (wide-angle for landscapes and indoors), and the 85 mm telephoto lens which excels in portrait photography and "over-shoulder images" in which a person in the foreground is deliberately kept out of focus.
Autofocus or manual focus?
A film-maker uses selective focus mainly for scene design purposes and therefore as a creative element of style. For this reason, camera lenses are used in the manual mode exclusively in videography even if they feature autofocus. In addition, all autofocus strategies fail in high quality videography such as measuring fields and face recognition. Although lenses for SLR cameras can be switched to manual mode, this is basically only a minor application. They often run imprecisely, or even with substantial play in the worst case, and the focal points that are so important for videography are difficult to reproduce.
Purely manual lenses such as the ZEISS lenses are designed for manual focal adjustment. They offer much better precision than manually operated autofocus lenses.
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| Fig. 1: Canon EOS-5D-Mark II equipped with the Planar T* 1.4/50 ZE and Chrosziel Follow Focus |
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| Fig. 2: Canon EOS-5D-Mark II used as a video-camera: ready-for-use Chrosziel rig equipped with the Planar T* 1.4/50 ZE, Chrosziel Follow Focus, Redrock Mattebox, and Marshall Field Monitor |
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Why lenses from Carl Zeiss are particularly well-suited for videography:
- Carl Zeiss lenses are characterized by their high speed and are designed solely for use as manually adjusted lenses – ideal for videography.
- They produce razor-sharp images and enable selective focus. Their maximum aperture of 1.4 is optimal as larger aperture stops such as 1.2 have such a small focusing range that the overall image appears blurred. Limitation to 1.4 is therefore a realistic value.
- The lenses come with an excellent manual focus ring whose motion is perfectly suited for follow-focus.
- The lenses have a special look, the images appear fresh and the bokeh effect (area of blur) appears very classy. The bokeh plays a particularly important role in the overall impression of the image.
Accessories for videographers
As soon as you start working with the new ZEISS lenses, you develop a desire for selective focus adjustment. The following accessories are helpful and recommended for this:
- Rig, lifting the camera to the standardized level of the optical axis and facilitating the attachment of follow focus and matte box
- Follow focus: despite the precise motion of the focus ring, it is difficult to smoothly and precisely adjust the focus using the lens ring. The follow focus should be as precisely as possible. Only then can the capabilities of these sophisticated lenses be fully utilized.
- Matte box to eliminate stray light and as a holder for filters such as ND (neutral density, for situations with too much light, sunlight, snow, etc.), polarizing filters (intensify sky, eliminate reflections) etc.
- Monitor for focus assessment, preferably with "peaking" display of the focal point using other colors
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| Fig. 3: The Planar T* 1.4/50mm equipped with gear ring (Chrosziel) for the follow focus. The reverse gear drive shown on the left is extremely important for intuitive operation. |
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Based on the technical data alone, it is difficult to explain the differences in pricing of the accessories which are substantial in some cases. It’s the details that count: for example the direction of focus shift. The follow focus supplied by Munich-based Chrosziel has a reverse gear drive which I find extremely important. The intuitive component offered by a reverse gear drive should not be underestimated. Intuitive means that you rotate forwards to move the focal point farther away. The precision of the rig is evident from the firm and fixed attachment of the parts and by how easy they are to disassemble when needed without hurting your hands.
Until now, Chrosziel has supplied a fixed gear ring for the standard zoom of Canon. The fixed ring that is seated directly on the lens ensures optimal precision that vastly exceeds the precision of flexible universal rings. Since the cameras are usually sold with this zoom, it is very wide-spread. However, it is not the optimal choice for high quality videography. Since I used to work with the DOF adapter quite a bit in the past, I became familiar with the advantages of the Canon FD lenses for purely manual focusing. It was therefore a great joy to me when purely manually focusing ZEISS lenses finally became available for Canon cameras. For my applications, it would also be ideal to have a manual aperture ring. Currently, the aperture stop is controlled electronically by the camera which is a slight drawback.
Chrosziel was kind enough to custom-manufacture a gear ring for my 50 mm lens – I cannot imagine better customer service. It has come to my attention that Chrosziel is considering adding fixed gear rings to their product line for ZEISS lenses. The crank on the follow focus is also very convenient and important to me: it makes it much easier for me to overcome the limited range of angles that can be set with my left hand. The monitor with peaking function is indispensable as it allows me to assess the focus properly. Chrosziel supplies the matching solution in an additional kit for this application as well.
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| Fig. 4: Carl Zeiss SLR lenses are ideally suited for precise follow focus. |
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| Fig. 5: The crank on the follow focus is a necessity, especially for camera lenses. |
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| Fig. 6: The matte box accommodates the filters and provides protection against stray light. |
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| Fig. 7: The matte box must be sealed tightly on the objective lens (here with neoprene) to prevent uncontrollable reflections from forming on the surfaces of the filters. |
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| Fig. 8: The fixed gear ring on the lens. |
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Objective lenses for videography and photography
The strengths of the lens – such as high-speed, razor-sharp images, a noble look and beautiful background blur – can also be advantageous to normal photography. Photographers must be aware of the following:
- Snapshots are not a strength of ZEISS lenses since focusing usually takes more time than with autofocus lenses.
- Planar-T* lenses are ideal for fully designed images with high aesthetic appeal.
- The imaging performance is so good and the images so sharp that checking via the measuring field of the camera does not provide sufficiently accurate feedback although it generally works. The manual assessment of focus via the viewfinder is also problematic, but the "live view" feature can help. It magnifies the image in the display by a factor of 5 to 10 and you can see how far the measuring field determination or rough setting using the viewfinder are from the true focal point. While this permits perfectly focused images, it takes time. Having a good monitor with a "peaking" feature significantly simplifies focusing in videography.
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| Fig. 9: Free-hand night exposure: made possible only by the high speed of the Zeiss 50 mm lens. |
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Conclusion
In my experience, the new SLR lenses from Carl Zeiss are first class and unparalleled in digital videography with the Canon EOS-5D-Mark II. As lenses for purely manual focussing, they are perfectly suited for this application. The brilliant look of the lenses, their crispness, and the stylish bokeh are excellent additions for photography unless you talking about snapshots and not well-balanced, perfectly-designed pictures for which you can takes your time. Nothing here is left to automatic controls! And this feature is the strength of these lenses. The photographer has everything under control and has the opportunity and the means to produce very good pictures.
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| | About Thoralf Abgarjan
Thoralf Abgarjan produces multimedia content for music and advertising: music composition and production for Expedia.de, Exquisa, Erdinger, ADAC, ÖAMTC, film projects for Koch-Universal, Musik-Media-Verlag, YAMAHA, ADAC, ÖAMTC and many others.
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October 2009 |
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