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TechnologyTelecentric lens systems for wide-field low-F# monochromatic imagingModern integrating CCD cameras with cooled detectors allow low-light level imaging of atmospheric phenomena. In many cases it is desirable that this imaging be monochromatic, so that spatial spectral data are obtained to relate to various excitation processes.Normal camera lenses have large ray angles to the principal ray throughout their optical path, and so are unsuitable for use with narrow-band interference filters. The shift of transmission wavelength with filter angle increases as the angle squared, so that larger ray angles rapidly requires much wider filters. To overcome this problem, telecentric systems can be designed, where the principal ray of all image-forming cones across the field of view cross the image plane parallel to the optical axis. Thus the maximum ray angles through the filter are determined only by the F-number of the lens. For low-light-level imaging, it is desirable to operate at the lowest F-numbers possible. Lower F-numbers mean higher ray angles through the filter, and so require wider-band filters. However, narrow-band filters are readily available at much larger diamaters than the imaging detectors (for example CCDs), so that high F-number images at the filter can be re-imaged to low F-number images at the detector. (The Lagrange Invariant is conserved: r x sin(α) = constant, where r is the image size and α is the half-angle of the image-forming cone.) Thus the philosophy of Keo Scientific optical systems is to use the largest diameter filter readily available at the desired bandwidth (typically 3-inch filters) to fill the filter area with a higher F-number telecentric image, and then to re-image at low F-number onto the detector. In this way we can effectively form monochromatic images (2.0 nm filter bandwidth) of wide-angle fields (up to 180 degrees fish-eye) onto imaging detectors at effective F-numbers as low as F0.7. There are many possible parameters to vary depending on the application, and many limitations determined by the availablility of commercially produced singlets, doublets and camera lenses. Keo Scientific have, through years of experience, an understanding of the many aspects of the design process, and can assist customers in planning an optimal system for their particular application.
High resolution video imaging of the aurora without the need for Video Cassette RecordersReal-time imaging of auroral phenomena at very high frame rates — from analog 30-fps TV cameras, to digital 1000-fps cameras — straight to hard disc via FireWire interface is now feasible, alleviating the need for video cassette recorders and eliminating the hassle of limited-length video tapes. In the case of remote field sites, operations can be controlled remotely via crontab or via the ssh command line. Keo Scientific make use of Terabyte FireWire harddiscs and FireWire-support in the latest Linux kernel to optimize throughput and maximize reliability and scalability.Keo Scientific personnel are also actively involved in the development of....
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