Technical description of FMI all-sky cameras

Description of the old all-sky cameras

Image of Imager The "old" all-sky cameras use a downward-looking film camera and a spherical mirror to image the whole sky. There are also three light standards and a small display that are imaged at the same time.

There are no filters, and the colours depend on the type of film that is used. The light standards have a known "colour" and can be used in calibrating the results.

Normally the camera takes one image per minute, but it is possible to take images every 20 seconds (for campaigns etc.). There are a couple of fixed exposure times; mostly an exposure of two seconds is used and every tenth image is exposed longer.

The operation of the imager is started and stopped manually, and after the film is full, one has to develop it before use. The films are the copied to video tapes (BetaCam) from which interesting events are digitised for computer use.

Technical specifications

Camera Baillard Bolex Type H 16 M-5 (16mm)
Camera objective Angenieux B 25mm, 1:0.95
Spherical mirror Segment 208.5mm, r=140.0mm, f=690mm
Image intervals 20s or 1, 2, 10, 20, or 60 minutes
Exposure times 2, 4, 8 or 16s
Green light standard FO4/G/300 (540nm)
White light standard FO8/W/300 (560nm)
Red light standard FO8/R/30 (608nm)

More information: Kirsti Kauristie