GB2469332A - Lens adaptor - Google Patents

Abstract

A lens adaptor 20 for coupling a lens with an aperture control lever to a video camera has an aperture actuator 14 for engaging with and moving the aperture lever on the lens. An externally accessible handle 12 is provided so that the aperture actuator can be moved when the lens adaptor is coupled to the lens and camera.

Description

MECHANICAL APPARATUS

This invention relates to lens adaptors for fitting stills photographic lenses to video cameras.

Typical lens adaptors for the above purpose are of simple construction, and have a fitting for mounting to a stills photographic lens, such as a Single Lens Reflex (SLR) camera lens, on a first face, and a fitting for mounting to a video camera on a second face. It is desirable to be able to mount SLR lenses on a video camera as such a mounting provides a cost-effective way of achieving e.g. telephoto or narrow depth of field effects using a video camera. A user of such an adaptor is saved the cost of video-camera specific lenses, as they can use SLR lenses already in their possession and many second hand SLR lenses are available for a low cost.

Older SLR lenses have, in addition to focus and possibly focal length (zoom) control rings on their outside, an aperture control ring on the lens body that allows a user to manually control the aperture of the lens, and hence the amount of light that passes through it and its depth of field. However, more modern SLR lenses, and in particular those designed to work with digital SLR cameras, have not got such an external control ring for the aperture, the aperture of the lens instead being controlled by the camera body when the lens is mounted to it. This means that, when using traditional lens adaptors with modern SLR lenses, the user is no longer able to control the aperture of the lens, as there is no control element on either the lens or lens adaptor. There is therefore a need for a lens adaptor that will allow manual control of the aperture of the lens when it is mounted to a video camera.

According to a first aspect of the invention there is provided a lens adaptor for coupling a lens to a video camera, the lens comprising an aperture control lever for adjusting the aperture of the lens, said lens adaptor comprising an aperture actuator for engaging with and moving an aperture control lever of a lens; and a handle for moving the aperture actuator, wherein the handle is externally accessible for allowing the aperture actuator to be moved when the lens adaptor is coupled to a lens and a video camera.

Preferably, the lens adaptor further comprises an aperture control ring, the aperture control ring being rotatably mounted on the body of the lens adaptor, further wherein: the aperture actuator is coupled to the aperture control ring; and the handle is coupled to the aperture control ring for rotating the aperture control ring and aperture actuator. This aperture control ring provides a cover for the slot in the side of the body of the lens adaptor to prevent the ingress of light, said slot being present in the case that the aperture actuator is rotated around the axis of the lens adaptor by the aperture control ring in order to allow the aperture actuator to move.

Preferably, the aperture control ring further comprises a recess complimentary with a protrusion on the body of the lens adaptor, for securing the aperture control ring to the body of the lens adaptor. This helps to secure the aperture control ring to the body of the lens adaptor and prevents excess strain being put on other components coupled to the aperture control ring.

Preferably, the recess on the aperture control ring is elongated to allow the aperture control ring to rotate within a certain limit. This prevents excess strain being put on the aperture actuator by preventing the aperture control ring from rotating past reasonable limits.

Preferably, the aperture actuator is coupled to the aperture control ring by a screw thread, for adjusting the aperture actuator. This allows the lens adaptor to control the aperture of different lenses with different aperture control lever configurations.

Preferably, the handle is mounted to the lens adaptor via a screw thread for providing a friction lock to prevent the aperture actuator from moving when the handle is fully screwed in. This provides a mechanism for fixing the aperture once it is set at a desired level.

The invention will now be described, by way of example, with reference to the drawings in which: Figure 1 is a schematic plan view of the lens adaptor from the first face; Figure 2 is a schematic side view of the lens adaptor; and Figure 3 is a schematic plan view of the lens adaptor from the second face.

The present embodiment depicts a lens adaptor for use with a particular type of SLR lens and video camera. However, the principles described may readily be adapted for use in other lens/camera combinations.

Figures 1, 2 and 3 show schematic views of an embodiment in accordance with the invention. Lens adaptor 20 comprises main body 2, a hollow cylinder with a flat, annular base, the base further having three camera attachment flanges 4 on its outer circumference.

Lens coupling apparatus 6 comprising a ring having three, inwardly protruding flanges is mounted on top of body 2 using three screws 8.

The camera attachment flanges 4 depicted in the Figures are suitable for coupling with a Sony (RTM) PMW-EX3 video camera. In order to be so compatible with the camera, the flanges 4 have an outer diameter of approximately 84 mm, compared with an outer diameter of 78 mm for the rest of the base of body 2. The flanges have a width of 35 mm. Other embodiments for coupling with different cameras may have different sizes, configurations and numbers of flanges, or even use a different type of fitting altogether, for example a bayonet fitting. Additionally, these different fittings may require a different shape main body 2, for example forgoing the flattened base and having a simple cylindrical body 2.

Lens coupling apparatus 6 as depicted in the Figures is suitable for coupling to Nikon (RTM) SLR lenses such as the G series designed for digital SLR cameras. Such a coupling is known, and available commercially. As the coupling apparatus is attached using screws 8, it is simple to remove lens coupling apparatus 6 and replace it with different coupling apparatus suitable for attaching different types of lens.

In this embodiment, the main cylinder of body 2 has an outer diameter of approximately 57.5 mm, and the overall length of body 2 is approximately 18 mm.

Nikon (RTM) DX lenses such as this embodiment is designed to engage with have their aperture controlled by the camera they are mounted to in normal use, as described above.

The control of the aperture is achieved by the camera body engaging with and actuating a lever that protrudes from the back of the lens. By moving this lever, the aperture of the lens is adjusted. In order to provide manual adjustment of the aperture of the lens when otherwise mounted it is therefore necessary to somehow engage with and move this lever.

There is an additional difficulty when trying to achieve this end in a lens adaptor as this must be carried out within the constraints of appropriate dimensions to ensure that focal lengths of lenses are taken account of. Furthermore, this adjustment is preferably achieved without allowing extra light to enter the camera-adaptor-lens assembly which may otherwise impair the image quality.

Lens adaptor 20 further comprises aperture control ring 10. This ring is shown with an extended base attached to it having conical sides that may be used for marking with graduations, calibrated or otherwise, to indicate the position of aperture control ring 10. In other embodiments, aperture control ring 10 need not have the extended base and, in extreme cases, may even comprise only a fraction of a ring, in such cases being mounted in some kind of track or retention mechanism or similar. Coupled to aperture control ring 10 is handle 12 that may be used to rotate the aperture control ring 10 around body 2. Handle 12 may be mounted to the aperture control ring 10 via a threaded hole, such that when handle 12 is "tightened" part of the handle engages with body 2 and forms a friction lock that impedes the rotation of aperture control ring 10.

Protruding through a slot (not visible in the figures) in the wall of body 2 and mounted to aperture control ring 10 is the aperture actuator 14. This lever extends into the void in the middle of lens adaptor 2, and when coupled to a lens is capable of abutting and moving the aperture control lever of the lens. As such, movements of the aperture control ring 10 via handle 12 actuates the aperture control lever of the lens and adjusts the aperture of the lens.

Advantageously, aperture actuator 14 may be threaded like a screw, to allow the adjustment of its protrusion for fitting lenses with different locations of aperture control levers.

The slot through which aperture actuator 14 extends preferably has its centre around 3 mm to 4 mm from the top of body 2, and extends approximately 29° around the body 2. Aperture control ring 10 may be equipped with a mechanism for preventing the ring turning so far as to put strain on aperture actuator 14 by pressing it against body 2. Such a mechanism may comprise, for example, a recess cut into aperture control ring 10 that is complementary to a protrusion in body 2 for the permitted range of motion. Such a protrusion, if on top of the control ring 10, may further serve to retain the control ring against the body 2 and therefore further prevent excess strain on aperture actuator 14 when the control ring 10 is pulled away from body 2.

A single embodiment of the invention has been described above, with some potential modifications laid out. The skilled man will realise that other modifications may be made to the embodiment described within the scope of the invention. For example, rather than the annular ring described for aperture control ring 10, the aperture control mechanism of the lens adaptor could be replaced with a single lever, pivoted at the body 2, that could be moved from the outside and engage with the aperture control lever of the lens. The invention should only be limited by the following claims.

Claims (7)

1. CLAIMS1. A lens adaptor for coupling a lens to a video camera, the lens comprising an aperture control lever for adjusting the aperture of the lens, said lens adaptor comprising: an aperture actuator for engaging with and moving an aperture control lever of a lens; and a handle for moving the aperture actuator, wherein the handle is externally accessible for allowing the aperture actuator to be moved when the lens adaptor is coupled to a lens and a video camera.
2. 2. A lens adaptor as claimed in claim 1, further comprising an aperture control ring, the aperture control ring being rotatably mounted on the body of the lens adaptor, further wherein: the aperture actuator is coupled to the aperture control ring; and the handle is coupled to the aperture control ring for rotating the aperture control ring and aperture actuator.
3. 3. A lens adaptor as claimed in claim 2, wherein the aperture control ring further comprises a recess complimentary with a protrusion on the body of the lens adaptor, for securing the aperture control ring to the body of the lens adaptor.
4. 4. A lens adaptor as claimed in claim 3, wherein the recess on the aperture control ring is elongated to allow the aperture control ring to rotate within a certain limit.
5. 5. A lens adaptor as claimed in any one of the claims 2 to 4, wherein the aperture actuator is coupled to the aperture control ring by a screw thread, for adjusting the aperture actuator.
6. 6. A lens adaptor as claimed in any preceding claim, wherein the handle is mounted to the lens adaptor via a screw thread for providing a friction lock to prevent the aperture actuator from moving when the handle is fully screwed in.
7. 7. A lens adaptor substantially as herein described with reference to and as shown in any combination of the Figures.