Lighting device with afocal projection optics and corresponding method of operation
A lighting device includes a light source configured to emit a light beam through an afocal projection optics along a propagation path of the light beam from a negative lens to a positive lens. The lighting device includes a further negative lens interposed and mobile along the propagation path of the light beam from the negative lens to the positive lens. The lighting device also includes an optical element interposed in the propagation path of the light beam between the negative lens and the further negative lens. The optical element includes a cylindrical lens, a prism or an axicon.
1. A lighting device, comprising:
a light source configured to emit a light beam through an afocal projection optics along a propagation path of the light beam from a negative lens to a positive lens;
a further negative lens interposed and mobile along the propagation path of the light beam from the negative lens to the positive lens; and
a mobile support member carrying at least two different optical elements selected from a cylindrical lens, a prism and an axicon, the mobile support member configured to selectively interpose in the propagation path of the light beam between the negative lens and the further negative lens an optical element selected out of said at least two different optical elements.
2. The lighting device of claim 1 , wherein the mobile support member comprises a motorized effect wheel.
3. The lighting device of claim 1 , wherein the negative lens comprises a simple negative lens.
4. The lighting device of claim 1 , wherein the positive lens comprises an achromatic doublet.
5. The lighting device of claim 1 , wherein one of the at least two different optical elements comprises the prism, and the prism includes a pyramidal prism.
6. The lighting device of claim 5 , wherein, when the pyramidal prism is selectively interposed in the propagation path of the light beam between the negative lens and the further negative lens, a tapered side of the pyramidal prism is facing towards the positive lens.
7. The lighting device of claim 1 , wherein one of the at least two different optical elements comprises the axicon, and when the axicon is selectively interposed in the propagation path of the light beam between the negative lens and the further negative lens, a tapered side of the axicon is facing towards the positive lens.
8. A method of operating a lighting device according to claim 1 , the method comprising moving the further negative lens along the propagation path of the light beam:
bringing it closer to the negative lens and away from the positive lens, or
moving it away from the negative lens and bringing it closer to the positive lens.
9. The method of claim 8 , comprising selectively changing the optical element interposed in the propagation path of the light beam.