BACKGROUND OF THE INVENTION: One problem associated with using photographic apparatuses such as cameras is that, on the one hand, the user wants to minimize the amount of excessive light entering the camera through the lens, also called stray light, and on the other hand, the user wants to obtain clear, crisp and sharp pictures by letting a sufficient amount of light enter the camera as described. Both of the above objectives should be accomplished without covering the corners or the sides of image projected onto the film.

One method of cutting down the stray light known in the art is by utilizing an extendable lens hood. This hood screens off superfluous light entering the lens from other direc- tions than those directly from the intended subject for the picture to be taken. To accommodate for different focal length lenses, the hood is usually arranged as a bellows, or similar extendable device, having a first end attached to the lens and a second end open towards the subject. The length of the bellows can be changed by sliding the second end of the hood on a saddle. An extendable lens hood of this type is described in US 4,497,549.

The user of the camera has to have some indication as to how far the lens hood can be slid forward for any given lens, without cutting of the corners or the sides of the picture projected on the film frame by the lens hood being slid forwards too far. This indication can be accomplished by supplying an engraved or otherwise marked scale on the saddle, indicating allowable positions for the second end of the hood for any given lens.

A possible drawback associated with the above lens hood is that the scale will be very complicated because the optimal setting of the lens hood not only varies with what lens is used, but also with what opening is set of the diaphragm of the lens and the actual focusing distance used. A smaller opening permits a further extension of the lens hood compared to a larger opening and a close focusing distance also permits a further extension of the lens hood than a focusing distance closer to infinity, i. e. far away subjects. Thus, if all possible settings for all possible lenses are to be taken into account, this will result in a scale having a large number of markings. Such a scale is practically impossible to produce. As an alternative, every lens could have its own lens hood with a scale pertaining only to that lens and having markings for different openings correlated to different focusing distances. Also this type of solution has drawbacks, the cost for the user being one, because the user would have to purchase several extendable lens hoods, one for each lens.

A further alternative is for the user to memorize, through experience, which extension length of the hood works best with which lens. This is probably a big drawback for most users who want to be able to use their camera without complicated, expensive and lengthy initial trial periods.

A further type of adjustable lens hoods is shown in US 4,441,794. A camera, having a fixed or variable focal length lens either fixedly or interchangeably attached to the camera, is provided with a sunshade mounted to the lens and having a fixed opening. The sunshade is provided with an axially adjustable mask within the sunshade. The mask may be mounted at either the front or the rear opening of a bellows, e. g. a bellows of accordion-type. The position- ing of the mask is performed using a gear mechanism which is coupled to the lens focal length setting mechanism and which is operated either electrically using electric motors or manually using the lens focusing ring.

A possible drawback associated with this lens hood system is that there is no provision to take into consideration what the actual diaphragm setting is of the lens. A larger diaphragm opening generally requires a larger lens hood opening and a smaller diaphragm opening generally permits a smaller lens hood opening to be used.

SUMMARY OF THE INVENTION: The object of the present invention is to provide an arrangement with which it is ensured that the above drawbacks are mitigated by providing a device and method for minimizing vignetting and stray light in a photographic apparatus, which device and method are easy to use but will give superior control over the amount of vignetting and stray light in all circumstances.

Said object is achieved by a photographic device comprising a camera body; an interchangeable lens, and an extendable lens hood, where said camera body comprises a first side having a first mounting device arranged to mount said interchange- able lens to said camera body and said extendable lens hood

is arranged to be mounted onto said interchangeable lens opposite to said first mounting device of said camera body and said extendable lens hood comprises a first drive means arranged to extend or retract, respectively, said lens hood, where said interchangeable lens comprises a first set of electric contact means which cooperate with a second set of electric contact means arranged on said camera body for electrically conveying information on the actual focal length setting, the actual focusing distance set and the diaphragm opening set in said interchangeable lens to a calculating means arranged in said camera body, said extendable lens hood further comprising a third set of electric contact means which cooperate with a fourth set of electric contact means arranged on said interchangeable lens for electrically conveying information on the desired setting for the extension of said lens hood, as calculated by said calcu- lating means, to said first drive means and/or conveying information regarding the actual extension of said lens hood to the calculating means of said camera body.

BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be described in greater detail in the following with reference to the accompanying drawings, in which Fig. 1 shows an elevational side view, as seen from the rear of the camera body, of a camera assembly according to the present invention, Fig. 2 shows an elevational side view, as seen from the front of the camera body, of a camera assembly according to the present invention, Fig. 3 shows an elevational side view of one embodiment of a first drive means according to the invention, and

Fig. 4 shows a top view of a camera body with the top removed.

PREFERRED EMBODIMENT: Figs. 1 and 2 show a photographic apparatus suitable for use according to the invention, in this example, a camera comprising a camera body 100, a film cassette 200, a rear camera body cover 300, an interchangeable lens 400, and an extendable lens hood 500. The camera could be either a still camera, i. e. for taking still pictures, or a movie camera, i. e. for taking moving pictures or sequences of still pictures.

The camera body has a first side 110 equipped with a first mounting device 120 for mounting the lens 400 to the camera body 100 and a second side 130 equipped with a second mounting device 140 for mounting the film cassette 200 or a rear camera body cover 300 to the camera body 100. The second side 130 is located opposite to the first side 110.

The first mounting device 120 is advantageously a standard- ized quick-change connection such as a bayonet fitting. A camera body top 160 is provided on the upper part of the camera body 100. The camera body top 160 may be a viewfinder of some sort such as a prism viewfinder or a collapsible hood. In Figs. 1 and 2, the camera body top is shown as a collapsible hood in its folded position. The film cassette 200 and the rear camera body cover 300 can not be mounted to the camera body 100 both at the same time.

The film cassette 200 is designed to carry a roll of film (not shown) and keep a film frame of the film in a flat state facing the camera body 100. The film cassette 200 may further have film winding means and film counter means (neither is shown in the Figs.).

In an alternative embodiment, a video camera is used, which of course does not use a film cassette but a video tape cassette.

The interchangeable lens 400 comprises a first set of electric contact means 410 which cooperate with a second set of electric contact means 150 arranged on the camera body 100 for electrically conveying information on the actual focal length setting, the actual focusing distance set and the diaphragm opening set in the interchangeable lens to a calculating means 170 arranged in the camera body, as shown in Fig. 4.

The extendable lens hood 500 is arranged to be mounted onto the interchangeable lens 400 opposite to the first mounting device 120 of the camera body. The extendable lens hood 500 comprises a movable front end 505, aimed away from the lens 400, and a fixed back end 507 which is attachable to the lens. The front end 505 and the back end 507 are connected by a extensible shading means 502, e. g. a bellows. The front end 505 has a first opening 506 and the back end 507 has a second opening 508 for admitting light into the lens when the lens hood is attached to the lens.

The extendable lens hood further comprises a first drive means 520 arranged to extend or retract, respectively, the lens hood in a direction A parallel to a longitudinal axis of the lens 400.

As shown in Fig. 3, the first drive means 520 advantage- ously comprises a two-part sled mechanism which comprises a first part 530 and a second part 540. The first part 530 is connected to the back end 507 and the second part 540 is connected to the front end 505 so that the front end is slidingly movable relative to the back end of the lens hood. The first drive means 520 further comprises one or

more sensors 525 for detecting the actual extension of the lens hood, i. e. the distance between the front end 505 and the back end 507, and a drive actuator means 522 for propelling the front end 505 of the lens hood via the second part 540 of the first drive means 520. The actuator means is advantageously an electric motor or, for manual operation, a lever or screw mechanism. The sensors 525 are electrically connected to the calculating means 170 in the camera body 100, which will be described below.

The extendable lens hood 500 further comprises a third set of electric contact means 510 which cooperate with a fourth set of electric contact means 420 arranged on the inter- changeable lens 400 for electrically conveying information on the desired setting for the amount of extension of the lens hood, as calculated by the calculating means 170, to the first drive means 520. Typically, four separate contacts are required for a manual lens hood, i. e. without a separate electric actuating means for propelling the driving means. For powering an electric actuator means, five or six contacts are necessary, depending upon if a separate ground is used for the electric actuator means.

The drive means 520 of the lens hood 500 is electrically connected to the calculating means 170 of the camera body 100 via the first set of electric contact means 410, the second set of electric contact means 150, the third set of electric contact means 510 and the fourth set of electric contact means 420, including electric leads (not shown) incorporated in the lens hood, lens and camera body for connecting the different sets of electric contact means.

The first drive means 520 advantageously gets its electric energy from a battery (not shown) stored in the camera body

100. This could be the same battery which powers the other electric functions of the camera or a separate battery.

The setting of the lens shade extension according to the invention may be performed either as an automatic operation or as a semi-automatic operation. The differences will be described below.

In the automatic operation, when a user changes the setting of the lens, either the focal length or the aperture (dia- phragm opening), the calculating means 170 in the camera body 100 is sent a signal from the lens via the first and second set of electric contact means 410,150 respectively and the calculating means then compares the actual setting of the extendable lens hood extension, read via the third and fourth set of electric contact means 510,420 respect- ively and the first and second set of electric contact means 410,150 respectively from the sensors 525 in the first driving means 520, with a pre-set value stored in a memory table, or the like, in the calculating means 170. If the actual setting of the extendable lens hood extension differs from the stored pre-set value, the calculating means issues a correction signal to the-first driving means which then proceeds to set the lens hood extension to the desired value.

It is also possible to use the device and method above together with an autofocus system to obtain a fully automatic system for focusing, aperture setting and lens hood extension setting.

In the semi-automatic operation, the lens hood extension displacement is performed manually but the calculating means 170 emits a signal when the amount of extension of the lens hood is correct and a different warning signal

when the lens is extended too much for the lens and its setting, i. e. when there is a risk of vignetting.

The lens hood 500 is advantageously combined with a removable mask (not shown) having a smaller opening than the first opening 506 of the front end 505 of the lens hood. The mask screens off incoming light to permit a shorter lens hood extension than otherwise necessary when using long focal length lenses. The lens hood is, in this case, also provided with means to detect (not shown) whether the mask is in place or not and to compensate the lens hood extension setting accordingly through the calculating means 170.

The invention lends itself to still cameras, both film and digital types, as well as to video and motion picture type cameras, but is especially advantageous for use with cameras having zoom lenses where the optimal setting of the lens shade is difficult or complicated to accomplish.

The invention is not limited to the description above nor to the examples shown on the drawings, but may be varied within the scope of the appended claims. For example, the shape of the cross-section of the extendable lens hood is shown as substantially quadratic or square but any suitable shape may be employed for the lens hood, for example substantially round. The extendable lens hood is shown as a soft bellows type lens hood, but could be shaped as plates or tubes which slidingly fit inside each other. An alternative to having electric contacts in the lens hood and lens, to perform the electrical contact between the lens hood and the lens/camera body, is to use an electric cable for connecting the lens hood sensors and first drive means directly to the camera body and the calculating means.