Infrared detection device and masking section

1. An infra-red detection device comprising:

an infra-red detection section;

a plurality of optical elements arranged to direct infra-red radiation to the infrared detection section; and

a masking section arranged to partially mask a first optical element of the plurality of optical elements, such that a first part of the first optical element is masked and a second part of the first optical element is not masked, and such that the masking section is arranged to attenuate infra-red radiation directed via the first optical element, wherein

the first optical element is such that a detection zone associated with the first optical element is unaffected by the presence or absence of the masking section, and

the first part of the first optical element is masked by a portion of the masking section that is opaque to infrared radiation.

2. The infrared detection device of claim 1 , wherein each optical element is a Fresnel facet.

3. The infra-red detection device of claim 1 , wherein the masking section partially masks optical elements positioned along respective first and second, substantially perpendicular, directions from the first optical element.

4. The infra-red detection device of claim 1 , wherein the masking section partially masks a lower optical element arranged, when in use, to have a detection zone lower than a detection zone of the first optical element.

5. The infra-red detection device of claim 4 , wherein attenuation by the masking section is less for infrared from the detection zone of the first optical element than for infrared from the detection zone of the lower optical element.

6. The infra-red detection device of claim 4 , wherein a proportion of the first optical element masked by the masking section is less than a proportion of the lower optical element masked by the masking section.

7. The infra-red detection device of claim 1 , arranged such that at least one upper optical element has a detection zone higher, when in use, than the detection zone of the first optical element, and the upper optical element is not blocked by the masking section.

8. The infra-red detection device of claim 1 , wherein at least one optical element is completely masked by the masking section.

9. The infra-red detection device of claim 1 , wherein the masking section is removable.

10. A kit comprising the infra-red detection device of claim 1 and a plurality of masking sections, the masking sections arranged to differ from each other by masking different optical elements and/or masking different proportions of the optical elements.

11. A method of modifying an infra-red detection device having an infra-red detection section and a plurality of optical elements arranged to direct infra-red radiation from respective detection zones onto the infra-red detection section, the method comprising:

partially masking a first optical element of the plurality of optical elements by placing a masking section such that a first part of the first optical element is masked by a portion of the masking section that is opaque to infra-red radiation, wherein

the first optical element is such that the detection zone associated with the first optical element is unaffected by the presence or absence of the masking section.

12. The method of claim 11 , further comprising removing previous masking section before partially masking the first optical element.

13. The infrared detection device of claim 1 , wherein the masking section has a slot shaped hole corresponding to an unmasked portion of the first optical element.

14. The infrared detection device of claim 1 , wherein the masking section is in contact with the first optical element.