Technical description of the emCCD all-sky imagers

Image of Imager The all-sky imagers that use the electron multiplication CCD technology are manufactured by Keo Scientific. Each imager has telecentric and non-vignetting optics, and the field of view of the fish-eye lens is 180 degrees. A mechanical shutter protects the filters and CCD from direct sunlight.

The filter wheel can accommodate eight narrow bandwidth interference filters. One filter holder is left "free" to be able to acquire non-filtered images. Every station has six filters: green, blue, red, and a background filter for each colour.

The signal-to-noise ratio and the dynamic range of this system are much higher compared to the previous generation devices. The imaging mode is frequently modified to be synchronised with other measurements in the same region but it typically consists of one green and one blue line image at least every 10 sec, as well as one red line image every 30 sec.Standard imaging modes include at least 20 images per minute. The data are stored in 16-bit png/jp2 files with 512x512 pixel resolution.
Photo: Jyrki Mattanen

Technical specifications

Fish-eye lens Mamiya Sekor 24mm f/4
Additional optics Telecentric lens elements
Filter wheel 8-position filter wheel for 3" filters
Filters Wavelengths 427.8nm, 438.0nm, 540.0nm, 557.7nm, 620.0nm, 630.0nm (BW 2.0nm)
Re-imaging optics Schneider Optics Inc. Century Achromatic Diopter +3.5
CCD camera lens Canon 50mm f/0.95
CCD camera Andor iXonEM + DU-888 (1024x1024 pixels)

More information: Kirsti Kauristie