Forum Übersicht - Objektive » Patentschrift zu den Minolta Portrayer-Filtern

Liebe Mitglieder,

Minolta hatte ab Mitte der achtziger Jahre zwei spezielle Weichzeichner-Filtersätze im Programm, das Minolta Portrayer Set P (speziell für die Portraitfotografie) und das Portrayer Set S (für allgemeine Weichzeichnungseffekte), die jeweils in E55- und E72-Fassung (leider hierzulande nur in diesen Größen) verfügbar waren (in Fernost gab es auch eine Variante mit E77-Fassung und eine mit quadratischen 76mm Filtern) und in mit rotem Filz ausgeschlagenen Holzschatullen oder (später) mit blauem Filz ausgeschlagene Kunststoff-Klappetuis angeboten wurden:
(E55) Minolta Portrayer Set P1 + P2 + P3 (7255-181, 0-43325-72009-3, Umkarton: 9202-7255-91)(E72) Minolta Portrayer Set P1 + P2 + P3 (7272-181)(E77) Minolta Portrayer Set P1 + P2 + P3 (7277-181) Siehe auch: http://www.mi-fo.de/forum/viewtopic.php?t=34287(#76) Minolta Portrayer Set P1 + P2 + P3 (7203-181) (Quadratische Filterscheiben aus Glas mit Abmessungen 3,0"x3,0" bzw. 76x76mm für einen speziellen Filterhalter. Der Minolta Gelatin Filter-Holder (6805-100) ist definitiv nicht geeignet, nicht nur weil dieser laut Anleitung für 3,0"x3,0" / 75x75mm Filter gedacht ist, sondern auch, weil die Filterscheiben für diesen Halter zu dick sind. Siehe auch: http://www.mi-fo.de/forum/index.php?showto...ost&p=99573)(E55) Minolta Portrayer Set S1 + S2 (7255-182)(E72) Minolta Portrayer Set S1 + S2 (7272-182)Insbesondere die P-Filter wiesen die meines Wissens bis heute einmalige Eigenschaft auf, selektiv nur die Hauttöne weichzuzeichnen, wohingegen andere Farbtöne unbeeinflußt blieben. Damit bot sich dieser Filtertyp insbesondere für die Portrait- und Aktfotografie an.

Vielleicht interessiert sich ja der ein oder andere für den technischen Hintergrund zu diesem Filtertyp. Nun, durch Zufall habe ich neulich die zugehörige Patentschrift gefunden, die sich mit der Fertigung und dem Funktionsprinzip dieser Filter befaßt:

http://www.google.com/patents?id=BJk9AAAAEBAJ

Patent number: 4480896
Filing date: 1982-01-18
Issue date: 1984-11-06
Inventors: Souichi Kubo, Yukio Okano
Assignee: Minolta Camera Kabushiki Kaisha

ZITATOptical filter suitable for portrait photography

Abstract

An improved soft focus optical filter is provided and comprises a plurality of effective filter areas on a transparent substrate. The filter areas are designed specifically to modify the modulation transfer function of the filter so that a selective soft focus effect is achieved only for transmitted green light.

[...]

Claims

What is claimed is:

1. An optical filter for use with a sharp imaging lens, comprising a transparent substrate and a plurality of transparent minute spots disposed at random on said substrate for producing a phase difference between a wave front transmitted through said spots and that transmitted through the portion of the substrate other than said spots, said phase difference. Delta. satisfying the following condition for producing a selective soft focus effect only for green light transmitted through said filter: ##EQU6## wherein m is an integer selected from 1, 2, 3 and 4, and. Lambda.G is a design wavelength selected within the green wavelength range.

2. The invention according to claim 1, said optical filter further satisfies the following condition: ##EQU7## wherein Aa is the smaller total area between the total area of said spots and the total area of the portion other than said spots, while Ab is the larger total area.

3. The invention according to claim 1, wherein said plurality of transparent minute spots comprise round spots of identical diameter.

4. The invention according to claim 1, wherein said plurality of transparent minute spots include round spots of different diameters.

5. The invention according to claim 1, wherein said plurality of transparent minute spots comprise ellipsoidal spots arranged so that the axes of ellipsis point to random directions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical filter for use with a photographic objective lens, and more particularly to an optical filter suitable for portrait photography.

2. Description of the Prior Art

A portrait photographed with an ordinary, sharp objective lens reproduces sharply the spots, freckles, wrinkles etc. of a face, thereby creating an unfavorable impression. To improve this, various soft focus lenses and soft focus filters with sharp lenses are provided. However, since such soft focus lenses and filters produce soft focus effects not only on the facial spots etc., but also on the other areas of the picture, for example, a dress, hair etc., a desirable portrait can not be obtained by them. Therefore, a desirable portrait in which the facial spots, freckles, wrinkles, and other common blemishes are reproduced softly and the other areas except for the human skin are reproduced sharply, is not obtained by the above-mentioned device.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical filter capable of producing desirable portrait photography with a sharp objective lens in such a way that a soft focus effect is produced on the color of human skin, such as a face, hands and feet, while a sharp tone effect is given to a dress, hair etc.

To attain their object, the inventors made subjective evaluation experiments on sharpness for various portraits produced by filters having selective soft focus effects only for a predetermined color. From the result of such experiments, the inventors have found that desirable portrait photography described above can be obtained by using a filter having a selective soft focus effect only for transmitted green light. The present invention provides such a filter suitable for portrait photography. The reason they are capable of obtaining a desirable portrait by such a filter is considered as follows. The human skin generally absorbs the green light because of hemoglobin in the blood, thereby causing its color to appear to be magenta. Facial spots, freckles, wrinkles etc. are distributed on the background of the magenta color. A facial image formed by use of optical filter having a selective soft focus effect only for green light, results in the spots, freckles etc. being imaged mainly by magenta light whose color is a complementary color of green, whereby the spots, freckles etc. become inconspicuous with an approximation in magenta color to the surrounding skin. For such reason, the optical filter according to the present invention, when used with a sharp lens, produces an entirely soft image with detailed facial contrast. Additionally, since this filter brings about no soft focus effect on the red and blue light ranges, most portions of an object, except the skin color, is imaged sharply. Therefore, by use of such and optical filter with a sharp lens, a desirable portrait in which the facial spots etc. are reproduced softly and the other portions except for human skin, for example, a dress, hair etc. are reproduced sharply, can be obtained.

[...][/quote]
Ein weiteres, wesentlich älteres Minolta-Patent zu optischen Tiefpaßfiltern legte bereits zuvor einige Grundlagen für diese Entwicklung.

Viele Grüße,

Matthias

PS. Zu Archivzwecken hier ein paar Aufnahmen dieser Portrayer-Filter: http://snapstill.blogspot.com/2009/06/mino...yer-fliter.html
http://www.sonydslr.com.tw/alpha/viewtopic...=10&t=17762