Observatory Dome

Hi,

I remember seeing an observatory with an unusual shutter, but I don't
remember where. It was a hemispherical dome which rotated in azimuth,
business as usual. The shutter as a round hole, which was on a separate
sector of the sphere. This sector would rotate as well in order to
change the altitude of the hole. Has anybody seen this ? I have no idea
where I saw this, but it's kind of cool.

Thanks.

Eric.