Forum Übersicht - SR-Bajonett-Objektive » Minolta VFC 2,8/24+Minolta 2,8/35 Shift CA-Patent

Liebe Mitglieder,

Ende der siebziger Jahre brachte Minolta einige sehr unübliche Objektive für die kreative, aber auch die wissenschaftliche Fotografie heraus, darunter auch zwei bis heute einmalige Objektive mit variabler Objektfeldkrümmung (variable field curvature = VFC), bei der man die Bildebene bei Bedarf durch Drehung an einem Ring am Objektiv stufenlos konvex oder konkav durchbiegen konnte.

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

http://www.rokkorfiles.com/24mm%20VFC.htm Minolta 2,8/24mm VFC
http://www.rokkorfiles.com/35mm%20Page%201.htm Minolta 2,8/35mm Shift CA

Das Shift-CA-Objektiv mit zusätzlicher Shift-Funktion wartete darüberhinaus auch noch mit einer seilzuggesteuerten Blendenübertragung von der Kamera ins Objektiv auf (eine bis vor kurzem technisch einmalige Lösung - erst die neuen Shift-Objektive von Nikon bieten ebenfalls eine automatische Blendensteuerung durch die Kamera an, inzwischen natürlich vollelektronisch). Auch die maximale Shift-Auslenkung des Objektivs wurde durch eine trickreiche Mechanik auf das jeweils optisch maximal zulässige Maß in Abhängigkeit von der Richtung der Auslenkung begrenzt.

Vielleicht hat Euch schon immer mal interessiert, wie die Funktion der variablen Objektfeldkrümmung eigentlich funktioniert hat. Nun, hier findet sich die zugehörige Patentschrift:

US-Patent 4231636 eingereicht von Minolta am 1978-07-19, Patent erteilt am 1980-11-04.

http://www.google.com/patents?id=Fy4wAAAAEBAJ

Hier die Einleitung:
ZITATBACKGROUND OF THE INVENTION

Variable field curvature lens system

Abstract

An optical lens system is provided having the capability of selectively varying the peripheral field curvature to improve focusing for nonplanar objects and for special photographic effects. The lens system can include in sequence, a first lens group of positive refractive power, a second lens group of negative refractive power and a third lens group of positive refractive power. The specific refractive power of the first and second lens group are designed so that the optical ray traces from an object on the optical axis at infinity will run approximately parallel with the optical axis in the space between the second and third lens groups. The first and second lens groups being movable as a unit relative to the third lens group to change the field curvature without varying the back focal distance of the lens system.

Inventors: Abe; Haruo (Sakai, JP)
Assignee: Minolta Camera Kabushiki Kaisha (Osaka, JP)
Appl. No.: 05/926,196
Filed: July 19, 1978

[...]

1. Field of the Invention

The present invention relates to an optical lens system and more particularly to an improved variable field curvature lens system.

2. Description of the Prior Art

Recently a relatively fast wide angle lens system was introduced in the commercial photography field. The design parameters of this system permitted the introduction of a variable field curvature (VFC) to render an object in sharp focus on the film plane, even though the object depth of field may be concave or convex relative to the flat image plane.

Ordinary photographic objective lenses are designed and aberrationally corrected so that all points in a perpendicular plane at which the lens is focused will appear sharp on the film. In practice, however, objects to be photographed are rarely confined to such a plane. Usually subjects are three dimensional with parts located at various distances from the camera. With the ordinary SLR flat-field objectives, the photographer has only the depth of field, which can be obtained from stopping down the lens, to rely upon to render such subjects or parts thereof in sharp focus. The variable field curvature lens permitted an object to be placed in focus not only along the optical axis but also the marginal or off axis points of the object can be placed in focus by a continuous changing of the curvature of field from flat to concave or to convex through the adjustment of a control ring on the barrel. This capability of permitting the varying of the curvature of field allows the photographer to achieve a sharp focus for rounded, recessed or other three dimensional subjects without relying solely upon the depth of field.

The photographer would also have the ability of using this bulging or recessed field to creatively render primarily two dimensional subjects deliberately out of focus at the center or around the edges of the field of view. This lens system further utilized a "floating" focusing system, in which relative movement of lens components were varied independently to provide edge to edge sharpness even at the closest focusing distances at full aperture. This automatic correction was operative and effective with either a flat field or any curvature introduced into the field to provide top image quality whether the lens was used as a special variable field curvature lens system or as an ordinary wide angle lens.

A mechanism for focusing a variable field curvature lens is disclosed in the U.S. Pat. No. 3,904,275. Additional relevant prior art can be found in a Japanese publicly available published patent application disclosure No. 48-2823, 1973 and the German Offenlegungsschrift No. 2224429, 1972.

A practical application for a variable field curvature lens system can be found in the television industry. Traditionally the light receptive surfaces of the ordinary image or vidicon tubes, have been flat. In attempting to record an object scene having considerable depth or an object scene wherein the prominent object features are curved, it is necessary to utilize a lens system that would provide a flat image plane for a curved object on the image tube.

Conversely, certain recent image tubes, for example, the highly sensitive image tube developed by Tokyo Shibaura Electric Company, Ltd., known as the SEM tube, have utilized light receptive surfaces which are curved. In this regard, it is necessary to bring a flat object scene into focus on a curved image light receptive surface. A suggested alternative comprises the use of an ordinary lens system and optical fiber elements to carry the flat image formed by the ordinary lens system to the curved light receptive surface, but such device would add considerable to the total cost of the video system.

Generally, the above variable field curvature lens systems have utilized at least two groups of lenses, front and rear, for ordinary focusing purposes. During focusing, the front and rear groups are shifted at a predetermined relatively different rate to prevent change of the curvature of field while for the purpose of introducing a variable curvature, the front lens group alone will be shifted along the optical axis. As can be appreciated, the front lens group must then be provided with a means of shifting it at a predetermined speed ratio with respect to the rear lens group and further a different mechanism for selectively shifting the front lens group alone during a VFC operation. This dual requirement complicates the construction and manufacturing of a variable field curvature lens system and accordingly increases its cost in an already extremely cost competitive photography field.

A relatively simple and cost competitive VFC lens system is still an object of the prior art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved variable field curvature lens system which permits the variation of the field curvature independent of any automatic compensation of the field curvature during a focusing operation.

It is another object of the present invention to provide a variable field curvature lens system wherein the relative positions of a first and second lens group can be held constant during a focusing operation and can be manually varied to permit the introduction of variable field curvature.

It is still another object of the present invention to provide a variable field curvature lens system wherein at least two relatively movable lens groups have complimentarily refractive powers to permit an optical ray trace from an object at infinity to parallel the optical axis as it exists from the image side lens group.

It is a final object of the present invention to permit the two relatively movable lens groups to be moved along the optical axis as a single unit relative at least a third lens group without varying the total back focal length of the lens system.

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 be best understood by reference to the following description, taken in conjunction with the accompanying drawings.

[...][/quote]
Ich hoffe, daß Sony irgendwann diese Ideen aufgreift und solche Objektive auch für das A-Bajonett herausbringt.

Viele Grüße,

Matthias

ZITAT(matthiaspaul @ 2009-01-08, 20:02) Ich hoffe, daß Sony irgendwann diese Ideen aufgreift und solche Objektive auch für das A-Bajonett herausbringt.[/quote]
Da habe ich schon 20 Jahre vergebens gehofft, daß Minolta selbst diese Optiken für Dynax bringen würde

Viele Grüße,

Manfred