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What is the bokeh of a projector lens?

What is the bokeh of a projector lenses without aperture blades, such as Leitz Hektor and Zeiss Visionar?


Lenses without aperture blades, such as projector lenses, often produce a unique bokeh different from traditional photographic lenses. The bokeh’s characteristics in such lenses are influenced by the absence of an adjustable aperture, leading to some distinct effects.

Circular Bokeh

Without aperture blades to shape the opening through which light enters, the bokeh produced by these lenses tends to be perfectly circular, assuming the lens itself is round. This is because there’s nothing to alter the shape of the out-of-focus light points, resulting in a bokeh that retains the natural roundness of the lens’s optical design.

Consistent Across Apertures

In traditional photography lenses, changing the aperture can affect the shape and quality of bokeh because the aperture blades form a more hexagonal or octagonal shape as they close. Since projection lenses and other lenses without aperture blades lack this mechanism, the bokeh quality and shape remain consistent regardless of the light entering the lens or the focus distance. The only variation comes from the inherent optical design of the lens and the distance relationships in the scene.

Smooth Transition Zones

The transition zones in the bokeh from in-focus to out-of-focus areas might appear smoother in lenses without aperture blades. This is due to the unobstructed pathway of light through the lens, leading to a more uniform rendering of out-of-focus areas. The smoothness of these transition zones can contribute to a more pleasing, less distracting background.

Influence of Lens Optical Design

While the absence of aperture blades leads to circular bokeh, the overall quality and character of the bokeh (such as its softness or the presence of optical aberrations like chromatic aberration) are still significantly influenced by the lens’s optical design. Elements such as the curvature of the lens elements, the glass quality, and any coatings applied to the lens surfaces will affect the bokeh’s appearance.

Creative Potential

Photographers and videographers sometimes use projection lenses adapted to cameras specifically for their unique bokeh characteristics. The circular, consistent bokeh can add an artistic or vintage feel to images and videos, especially when a dreamy or ethereal background is desired.

Projector Lenses Examples

Lenses without aperture blades, like Ernst Leitz Wetzlar Hektor’s 85mm f/2.5 projection lens (sample image of the post), offer a distinctive bokeh that can be highly valued for creative photography and filmmaking. The absence of aperture blades simplifies the optical path, often resulting in a natural, circular bokeh that many find appealing for its simplicity and consistency.

Zeiss Jena Visionar Projector Lenses

Zeiss Visionar projector lenses, such as the 141mm f/1.9 and 119mm f/1.9, are intriguing examples of optical engineering originally designed for scientific and industrial applications, primarily projection systems. These lenses were engineered to deliver sharp, clear images in projection settings, making them ideal for detailed visual tasks. Due to their construction, Visionar lenses offer excellent light gathering and depth of field, highly advantageous features in their native projection roles, and are also appealing for photographic experimentation.

Adapting Visionar lenses for mirrorless and DSLR photography is becoming popular among photographers who value these lenses’ distinct optical characteristics, such as their ability to produce exceptionally smooth and creamy bokeh, thanks to their large apertures. The lenses’ bokeh often features a circular and uniform appearance, sometimes accompanied by a slight swirl that gives images a dramatic, vintage-like effect. This makes them particularly favored for portraits and artistic photography, where the photographer aims to highlight the subject with a vivid separation from the background or to impart a unique aesthetic to their images. Zeiss Visionar lenses are easy to adapt to modern cameras as their tube diameter is circa 62.4mm, and they fit into the M65 helicoid directly, or you can use an M65 extension tube with clamps and a helicoid attached to it. An M65 to EOS or RF adapter should be used to shorten the distance between the lens rear glass and the sensor to achieve infinity.

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