1. Field of the Invention
The present invention relates to a varifocal lens for a TV camera which in particular may be mounted on an end scope, having a lens barrel, which is provided with guide indentations for radial pins may be moved toward each other for setting the focal length and together for focussing.
By way of illustration, TV cameras have increasingly been employed for taking endoscopic pictures. Such TV cameras must be as small and lightweight as possible in order not to hamper the physician during the operation. TV cameras with varifocal lenses, which would permit adjustment of the field of vision and adaption to various instruments have, for this reason, only been proposed now and again without having had any particular impact in practice.
An object of the present invention is to provide as small and light as possible a varifocal lens for a TV camera, which is particularly meant to be mounted on an endoscope.
An inventive solution to the object of the present invention and its further embodiments is described in the following.
An inventive step is that the lens barrel is guided in a support bearing, which is fixed in relation to the encasement of the TV camera, in such a manner that it can be moved in the direction of the optical axis of the lens and is secured to prevent rotary motion. Furthermore, the guide indentations are slits, which are open at the front and at the back and consist of a straight section abutting upon the front or rear end of the barrel and running parallel to the optical axis, a section running concentrically to the optical axis, and the hereto abutting actual cam for controlling the movement of the lens groups.
As a result the following advantages are yielded:
The lens mounting can be inserted into the lens barrel through the front or rear slits in such a manner that the lens barrel does not have to be constructed out of two half shells that consequently would have to be securely joined by means of a medium, thereby increasing the diameter. The support bearing, which prevents rotary motion while permitting moving the lens for focussing, does not increase the diameter of the varifocal lens.
Due to the one-piece construction of the lens barrel, it suffices to arrange onto the lens barrel a second barrel in such a manner that it can be rotated, the inner surface of which is provided with indentations running parallel to the optical axis for the pins to engage. The focal length of the varifocal lens can easily be set by turning this second barrel.
For varying the focal length, the second barrel may, of course, be turned manually or by means of a setting lever.
However, it is particularly advantageous if a tooth system is provided on the outer surface of the second barrel, which meshes together with a castellated wheel, as in this manner a simple knurled wheel on the outer side of the varifocal lens is all that is needed for setting the focal length permitting, as opposed to a setting ring that runs concentrically to the optical axis, easy one-handed operation for setting both the focal length as well as focussing. The knurled wheel for focussing may, by way of illustration, engages the eccentric, elliptical indentations in the second barrel by means of pins.
The stability of the slit lens barrel and a steadiness of the setting are substantially increased by means of the further embodiment wherein the lens mountings, on the one hand, give the lens barrel stability and, on the other hand, as a result of this embodiment they cannot tip.
A further embodiment described in claim 4 hereto, which is provided with two lugs that run parallel to the optical axis, makes very compact assembly possible as the support bearing can be provided at the point of separation between the lens and the tube for the TV camera, where it takes up practically no additional room.
Yet a further embodiment, which is provided with knurled wheels for focussing as well as for setting the focal length, is ergonomically advantageous, as it makes one-hand operation possible without changing the lever position.
A water protection rim also contributes to solving the object to of the present invention as no measures that would increase volume or weight, like those required according to the state of the art, are needed when flanging the varifocal lens to an endoscope in order to prevent water from running onto the front cover.