Forum Übersicht - SR-Bajonett-Objektive » Das Minolta Varisoft-Objektiv 2,8/85mm in Patenten

Liebe Mitglieder,

neben anderen unkonventionellen Lens Designs brachte Minolta im Laufe der Jahrzehnte auch zwei Soft-Focus-Objektive auf den Markt, bei denen der Grad der Weichzeichnung stufenlos einstellbar war.

Das erste dieser Objektive erschien 1977 für das Manuell-Fokus-System mit SR-Bajonettanschluß und MC-Kupplung, das Minolta Varisoft 2,8/85mm, eine Konstruktion mit sechs Linsen in fünf Gruppen. Im Laufe der Jahre erschienen drei Varianten des Objektivs, die sich allerdings nur im Aufdruck unterschieden. Zunächst hieß das Objektiv Minolta Varisoft Rokkor 2,8/85mm und Minolta Varisoft Rokkor-X 2,8/85mm, später dann einfach nur Minolta Varisoft 2,8/85mm. Eine dedizierte MD-Variante des Objektivs gab es meines Wissens nicht. Der Weichzeichnungseffekt, der durch ein einstellbares Maß sphärischer Abberationen erzeugt wird, hängt auch stark von der verwendeten Blende ab, weshalb eine Verwendung des Objektivs in Blenden- oder Programmautomatik - außer in Varisoft-Stellung "0" - nicht besonders sinnvoll erscheint.

Da MINMAN im Moment leider nicht verfügbar ist, verweise ich zur Illustration dieses Objektivs auf Rokkorfiles:

http://www.rokkorfiles.com/85mm%20Page%201.htm

Viele Jahre später brachte Minolta 1994 dann das Minolta AF 2,8/100mm Soft Focus für das SLR-System rund um das A-Bajonett heraus, ein echtes Autofokus-Objektiv mit 7 Linsen in 7 Gruppen und ebenfalls mit stufenlos einstellbarer Weichzeichnung. Sony hat dieses optisch hervorragende Portraitobjektiv leider nicht in das eigene Objektivprogramm übernommen.

http://www.mhohner.de/sony-minolta/onelens/af100f28soft

Wie auch immer, vielleicht hat Euch schon immer mal interessiert, wie eine solche Varisoft-Funktion eigentlich funktioniert. Hier finden sich die zugehörigen Patentschriften, in denen etliche mögliche Varianten solcher Objektive vorgestellt werden:

US-Patent 4124276, eingereicht von Minolta am 1976-12-15, Patent erteilt am 1978-11-07:

http://www.google.com/patents?id=MCs4AAAAEBAJ "Soft Focus Lens System"

Einleitung:
ZITATSoft focus lens system

Abstract

A variable soft focus lens system particularly adapted for photography is provided. The soft focus lens system includes at least two lens groups defining a meniscus shaped air space there between. The relative width of the air space can be variable by movement of one of the lens groups relative to the other. This movement can introduce a controlled amount of spherical aberration to provide within certain parameters a soft focus image with an acceptable Petzval sum and flatness of the image plane. Various embodiments of the present invention within the inventive parameters can be utilized and include both stationary and variable soft focus lens system.

Inventors: Okano; Yukio (Minamikawachi, JP), Nakamura; Akiyoshi (Sakai, JP), Ogura; Toshinobu (Tondubayashi, JP)
Assignee: Minolta Camera Kabushiki Kaisha (JP)
Appl. No.: 05/750,824
Filed: December 15, 1976

[...]

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an objective soft focus lens system for use in photography and more particularly to an improved soft focus lens system that eliminates undesirable aberrations.

2. Brief Description of the Prior Art

Soft focus lens system have been used in the photography field for a considerable period of time. Various different soft focus lens systems have been suggested such as those disclosed in U.S. Pat. No. 2,233,591; U.S. Pat. No. 1,370,885; U.S. Pat. No. 3,843,235; U.S. Pat. No. 3,397,023; U.S. Pat. No. 3,045,530; U.S. Pat. No. 2,959,105 and U.S. Pat. No. 3,476,457. Various apodization optical systems have also been described for achieving a blurred or soft focus image of a target photographing object. Frequently, soft focus filters have been suggested which are permanently mounted in a lens barrel, traversely removable from the lens barrel or attached to the end of the lens barrel.

One of the known ways of designing a soft focus lens system is to intentionally increase the amount of spherical aberration beyond the normal tolerance limits. By varying the spherical aberration introduced into the image an adjustable soft focus lens system can be achieved and such a system is disclosed in British Pat. No. 198,569 published June 7, 1923. The object of the British patent reference was to provide a soft focus objective and high speed anastigmatic combination lens system. This was accomplished by providing at least two sets of lenses wherein one lens was adjusted relative to the other lens set for the purpose of changing the lens from an anastigmatic to a soft lens.

The prior art has experienced difficulties in achieving a satisfactory commercial soft focus lens system that can be economically produced free from undesirable aberrations. These undesirable aberrations are usually introduced into the lens system by any variation in the introduction of spherical aberration. Frequently, the focus of the lens of the total lens system is usually not maintained during the variation of the spherical aberration and the operator has to re-adjust the focusing of the total lens system when the spherical aberration is varied. As can be readily appreciated the adjustment of the focus of the total lens system can be difficult when viewing a soft tone image through the viewfinder.

The prior art has not suggested an improved soft focus lens system that is capable of providing a highly desirable portrait image with a minimum of aberrations.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved soft focus lens system wherein the resulting softness of the transmitted image can be varied by changing the degree of spherical aberration without introducing additional undesirable aberrations.

Another object of the present invention is to provide a soft focus lens system which can be initially focused and maintained in a focused position irregardless of the variation in the softness of the transmitted image.

Still another object of the present invention is to provide an improved soft focus lens system wherein the form of the transmitted image is continuously variable between a sharp tone and a maximum soft tone while being kept in a focused condition with a minimal introduction of undesirable aberration.

A further object of the present invention is to provide an improved soft focus lens system which is capable of transmitting a soft focused point image consisting of a finally focused nucleus and a flare surrounding it for performing an ideal soft tone picture.

An improved soft focus lens system is provided having a pair of lens groups. Means are provided for varying the position of a first lens group relative to the position of the second lens group for varying the spherical aberration introduced into the lens system to provide a desirable soft focus transmitted image. Means are also provided for maintaining the focus condition of the total lens system during any variation of the position of the first lens group and the second lens group. A meniscus shaped air space can be formed between the first and second lens group and can be variable during the introduction of the spherical aberration. The first lens group can have a rear refracting surface that is concave to the point of intersection of an off-axial ray trace with the optical axis. A second lens group can have a second refracting surface also concave to the point of intersection and forming with the first refracting surface the meniscus shaped air space. The radius of curvature, r.sub.A of the first refracting surface and the radius of curvature, r.sub.B of the second refracting surface may be determined within the following ranges, respectively with the focal length of the lens system represented by f:

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

[...][/quote]

US-Patent 4214814, eingereicht von Minolta am 1978-03-07, Patent erteilt am 1980-07-29:

http://www.google.com/patents?id=vb08AAAAEBAJ "Variable Soft Focus Lens System"

Einleitung:
ZITATVariable soft focus lens system

Abstract

A variable soft focus lens system particularly adapted for photography is disclosed. The lens system incorporates two lens groups, a first object side lens group having an image side, rearmost surface convex to the image side, and a second, image side lens group having an object side, foremost surface concave to the object side. An airspace separating the first and second lens group has a meniscus shape concave to the object side. A good quality soft tone image having undersirable aberrations well within tolerable limits, is attained by shifting at least the second lens group along the optical axis relative to the first lens group whereby the airspace separating the two lens groups and a spherical aberration of the entire lens system is varied. An image does not lose proper focus while the spherical aberration of the system is varied. The second lens group has a refractive power within specified limits in relation to the refractive power of the entire lens system.

Inventors: Ogino; Shuji (Osaka, JP), Ogura; Toshinobu (Tondabayashi, JP), Okano; Yukio (Osaka, JP), Nakamura; Akiyoshi (Sakai, JP)
Assignee: Minolta Camera Kabushiki Kaisha (Osaka, JP)
Appl. No.: 05/884,357
Filed: March 7, 1978

[...]

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a soft focus lens system, and more particularly to a soft focus lens system for use in photography wherein the image quality is capable of being altered to achieve a desired degree of softness as a result of varied spherical aberration of the lens system.

2. Brief Description of the Prior Art

Soft focus lens systems have been used in photography for a considerable period of time. Various different soft focus lens systems have been suggested such as those disclosed in U.S. Pat. No. 2,233,591; U.S. Pat. No. 1,370,885; U.S. Pat. No. 3,843,235; U.S. Pat. No. 3,397,023; U.S. Pat. No. 3,045,530; U.S. Pat. No. 2,959,105; U.S. Pat. No. 3,476,457; U.S. Pat. No. 1,463,132 and U.S. Pat. No. 1,446,634. U.S. Pat. No. 2,381,098 discloses a lens system wherein movement of the lenses may introduce or remove softness of an image.

One of the known ways of designing a soft focus lens system is to intentionally increase the amount of spherical aberration beyond the normal tolerance limits acceptable in sharp focus photography.

Some soft focus lenses known in the prior art have been designed to permit variation of the spherical aberration of the lens system thereby allowing the photographer to obtain a desired degree of softness of a photographic image.

Such prior art lenses with variable spherical aberration usually comprise a three-group lens system having an intermediate negative lens group, shiftable along an optical axis, and a lens system including a shiftable front element, the latter being disclosed in British Pat. No. 198,569, published June 7, 1923.

Generally in order to obtain a soft focus image, it is sufficient to generate only a large spherical aberration, with other undesirable optical phenomena such as astigmatism, coma and other aberrations preferably being corrected as it is conventionally done in ordinary photographic lenses. The prior art systems have not enabled one to obtain an entirely satisfactory soft-focus picture because varying the spherical aberration is usually accompanied by deteriorations in other aberrations, thus rendering a resulting picture more or less indistinguishable from a picture taken with a poorly compensated lens. Furthermore, since shifting of any lens group to vary the spherical aberration brings the lens system out of focus, it has been necessary to refocus the lens system every time a change in the spherical aberration has been made as the lens system was adjusted to obtain the desired degree of softness. It can be readily appreciated that adjustment of the focus of the entire lens system can be difficult when viewing a soft tone image through a viewfinder.

The ordinary soft focus lens of the prior art having a preset non-variable spherical aberration, is always in a soft-focus condition and, as a result does not lend itself well to focusing when it is used as a lens for a single reflex camera.

Improvements in the design of soft focus lens systems including the feature of variable spherical aberration were suggested by U.S. Pat. No. 4,124,276 issued on Nov. 7, 1978 which is assigned to the same assignee as the present application. The variable soft focus lens systems disclosed in that patent require however, that at least two lens groups be shifted at different rates along the optical axis as a variation in the spherical aberration is made, as shifting only one of the lens groups so as to create a soft image would result in an unacceptable defocusing of the image. Shifting two or more lens groups at a differential speed, as it is necessary in that system, however requires an elaborate mechanism.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a variable soft focus lens system wherein the amount of spherical aberration is variable while other aberrations are properly corrected.

It is another object of this invention to provide a variable soft focus lens system of simple construction which permits selective variation in spherical aberration while maintaining the object in focus.

It is still another object of this invention to provide a variable soft focus lens system wherein, with the object being maintained in focus, the spherical aberration can be selectively varied by shifting only a single lens group.

The above stated and other objects and advantages are attained by a lens system having two lens groups separated from each other by an airspace. A first lens group has an image side surface convex to the image side and a second lens group has an object side surface concave to the object side. The airspace between the first and second lens group has the shape of a meniscus concave to the object side.

The lens group on the image side has a refractive power limited to a small value within a range defined by the formula

wherein. PHI. is the refractive power of the entire lens system and. PHI..sub.B is the refractive power of the lens group being located on the image side.

The spherical aberration of the entire lens system may be varied, and therefore may be adjusted to attain a desired degree of softness of the image by moving the image side lens group along the optical axis and thereby increasing or decreasing the meniscus shaped airspace between the two lens groups. Focus of the image is maintained while the spherical aberration and thus the desired degree of softness is selected.

The design of the lens system of this invention permit a rather simple construction of a barrel in which the lens system is mounted, as only the second, image side lens group is shifted when the spherical aberration is adjusted. The desired spherical aberration and hence the softness of the image is attained in this lens system while other undesirable optical phenomena such as astigmatism are minimized thereby providing a good quality soft picture.

The object side lens group of the present invention may be of any type such as those of the Tessar, triplet or Gauss type while the second, image side lens group preferably comprises two lenses.

The features of the present invention which are believed to be novel are set forth in particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings.

[...][/quote]

Viele Grüße,

Matthias