The Kodak 12-inch 305mm F4.8 soft focus portrait lens is mounted in a Number 5 Universal shutter.
Think about the 1950s glamour portraits of Hollywood stars like Marilyn Monroe, and this is what this lens creates.
The soft focus effect of this lens is obtained by controlled spherical aberration, which is much different than lenses that use chromatic aberration.
Spherical and chromatic aberration are two types of optical aberrations that can affect the performance of lenses, including their ability to create a soft focus effect. Early 19th-century meniscus single-element lenses are good examples of lenses that have chromatic aberration. As optical engineering improved over the decades, more complex lens designs like the achromatic doublets started addressing this aberration.
With “perfect” tack sharp lenses in the 20th and 21st centuries being the norm, photographers seek out the vintage 19th century lenses because of their flaws that produce a softer and more ethereal image. The optical engineers of that time worked hard to eliminate those errors and now companies in the 21st century like LensBaby and Lomography for example are creating lenses based on these optical designs. It is a funny world in which we live.
Spherical Aberration:
- Definition: Spherical aberration occurs when light rays passing through different parts of a lens are focused at different points. This happens because the shape of a spherical lens causes light rays passing through the edges to bend differently than those passing through the center.
- Impact on Soft Focus: Spherical aberration can produce a soft focus effect. It creates a slight blur, as not all the light converges at the same point. This can be desirable in some photography and cinematography applications, where a softer, dreamier look is preferred. Lens designers sometimes intentionally introduce spherical aberration to achieve this effect.
Chromatic Aberration:
- Definition: Chromatic aberration, also known as color fringing, is caused by a lens’s inability to focus all colors of light at the same point. It happens because different wavelengths of light (different colors) are refracted by different amounts as they pass through a lens.
- Impact on Soft Focus: Chromatic aberration typically manifests as colored fringes around high-contrast edges in an image. While it doesn’t directly contribute to a soft focus effect, it can degrade image quality. High levels of chromatic aberration can create a sense of softness, but this is usually considered an undesirable distortion rather than a pleasing, artistic effect. This type of aberration also can look sharper on the ground glass and then produce a much softer image on film. Field testing is required to confirm the actual soft focus effects at various apertures.
