Change page style: 

NICI Pupil Masks

You are here

Pupil masks together with the Focal Plane Masks define the coronagraphic configuration of NICI.   Pupil masking is accomplished with two mechanisms: the Spider Mask wheel and the Pupil Mask wheel.

The Spider Mask wheel provides a fixed-size mask for the telescopecentral obscuration, as well as the telescope spider vanes. The mask rotatesautomatically to maintain vane alignment as the telescopetracks. The mask's central obscuration radius is 0.270 x the telescope pupil radius, compared to 0.164 for the telescope central obscuration.The mask spider vanes are 30 times the thickness of the imaged telescope vanes.

The Pupil Mask wheel provides a selection of masks to stop down the outer edge of the telescope pupil. In the optical path, thiswheel lies behind the spider rotator and ahead of the beamsplitter. The available Lyot masks are listed below. Since theSpider Mask includes the central obscuration, the initial Pupil wheel maskshave none; they are simply holes cut in metal plates with no substratein order to eliminate one transmissive element. We recommend the use of the 95% pupil mask.

NICI Pupil Mask Wheel
Position Mask Name /
Diameter as % of Pupil
Gemini ID
1 Block --
2 95% G5731
3 90% G5732
4 85% G5733
5 80% G5734
6 Apodized G5735
7 Open --
8 100% G5730

Gemini Observatory Participants