Keo Sentry

Keo Sentry Imagers for Airglow Research

The Keo Sentry, originally designed by Dr. Robert Eather based on his extensive field-experience in Antarctica, is the classic workhorse of allsky and narrow-field airglow imaging. Through careful optical design, all-sky (fisheye) imaging at speeds as fast as f/0.95 can be performed even through interference filters with bandwidths as narrow as 18Å FWHM. Constant, incremental improvements, based in large part on valuable customer feedback, have resulted in an imager that is more sensitive and robust than ever before. The included field-proven KeoSynopticx automatic ephemerides-driven instrument control & data acquisition software ensures a truly turn-key solution. The features and capabilities of this Windows software is described in its User Manual. If preferred, Linux data acquisition software (no GUI) can be provided instead.

In addition to the standard fisheye (180 deg) field-of-view (FoV), convenient field-replaceable "FoV Modules" of 10, 20, 30, 50, 60, and 80 degrees, useful for high-resolution or cross-scale studies, are available off-the-shelf. Custom FoVs (down to 1 degree, telescopic) can be supplied upon request.

The Sentry can be built with either 3" or — for the very highest spatial resolution and sensitivity — 4" diameter optics (this is also the diameter of the filters used). Both single-filter drawer and filter-wheel based (6- and 8-slot wheels) models are available. The filter-wheel is carefully temperature stabilized with internal heating (and optional cooling) for optimum performance of the temperature-dependent narrow-band interference filters. Filters are "imaging quality" and optimized for the optical cone-angle under which they operate. All interference filters are custom manufactured to Keo Scientific's own demanding specifications. A wide range of filters, both narrowband and wideband, suitable for airglow/nightglow research is available. Some of our most popular stocked pieces are 557.7, 589.3 (Na), 630.0 nm, 777.4 nm, 865 nm, and notched wideband OH filter. We also provide suitable "background continuum emission" filters. We order these in relatively large quantities from the manufacturer and are able to pass them on to the research community at highly advantageous prices — some more information may be found in this brochure.

Sensor-head options include a range of Scientific Grade-1+ (hand-picked by the manufacturer for Keo Scientific Ltd.) back-thinned EMCCDs and CCDs (13.3 x 13.3 mm to 27.6 x 27.6 mm) with quantum efficiencies better than 95%, maintenance-free thermoelectric cooling down to -80 degrees C and lifetime vacuum guarantee. Deep-depletion or anti-fringing techniques are applied to CCDs/EMCCDs to eliminate or suppress "etaloning" effects in the NIR. Princeton Instruments QE curves are shown on the right.

Full spectral and flat fielding calibration services are available for your imager.

The imager may be controlled by any computer equipped with USB2 ports. A custom-built and pre-configured computer, with all software installed & fully tested, can be provided with the imager, as an option. This server-class (for reliability) computer comes in a robust shipping case which doubles as a 19-inch (6U) rack-mount unit. Conveniently, the filterwheel control unit included with your Keo Sentry imager can be mounted inside this same rackmount, for a tidy, well-organized field site.

A high-reliability capping shutter and a bright-light protection sensor mechanism is provided with all Keo Sentry imagers in order to prevent the sun from being focussed directly onto filters during daytime. This internal shutter does however not protect the imager's fisheye (or other primary) lens. We recommend using a Keo SunShield clamshell external shutter (sketch on the left), available separately — or a similar home-made scheme (please ask us for advice) — as an external shield to protect your imager's wide-angle primary lens from potentially harmful exposure to sunlight during daytime, especially at low latitudes. It is important that the mechanism used retracts fully below the lens, so as to not obscure any portion of the 180 degree field of view of a fish-eye lens.

Keo Sentry imagers (whether with or without a SunShield) will fit under our (optional) optical-grade hemispheric BK-7 glass domes. This 9.25” diameter observing port is made from BK-7 grade mineral glass. It is coated with a Silicon Oxide coating on the convex surface and with a Broad Band Anti Reflective coating on the concave surface. The SiO2 coating is an extremely resistant type of coating with a 0.01% reflective index, providing unparalleled light transmission. Both the SiO2 and BBAR coatings not only prevent internal and external reflections but also protect the surface from scratches, thereby extracting maximum optical performance from your Keo Scientific airglow imager. As opposed to many acrylic domes, this glass dome is truly Optical Grade, in that it has excellent transmission properties across the spectrum, and introduces no image distortion/warping across the field.

Based on blueprints of your observatory (or an accurate sketch of the area underneath your observing dome), we can provide a custom mounting solution (example, with azimuthal adjustability, shown in photo). We also provide a more "standard" free-standing solution (Keo Stock Item #2645) that can be oriented in any azimuth on your own pedestal or bench (this design has a built-in zenith angle adjustment for narrowfield observations). If you wish to design your own mounts, we recommend extruded aluminium T-slot from 80/20. We will provide you with CAD Drawings and/or 3D models of our imagers in order to aid you in your design work. Our imagers weigh up to 50 lbs, and we recommend a mounting structure that can carry at least twice that mass.

We can also provide you with our Environmental Monitoring & Control package (Keo Stock Item #2867), specifically designed with the proper long-term functioning of Keo instruments in mind. This kit includes IP network temperature logging, monitoring, and control (remote web accessible), thermostatically controlled fans and heaters, temperature and humidity sensors, with all ducting and mounting hardware included. A Stray Light Mitigation Kit is also available (Keo Stock Item #2868).

All imagers are supported by Keo Scientific's 3-year warranty and our famous "go-that-extra-mile" lifetime prompt, free (and cheerful) support service.

This product is carefully customized according to the individual researcher's unique scientific objectives — through extensive email interaction at the outset of the ordering process — and the overall design is constantly being improved upon, so it is hard to come up with a standard/generic "brochure" (which is often requested of us). However, here is some downloadable information relevant to our 3-inch Sentry and our 4-inch Sentry.

The Space Weather section of our site shows some additional imager models, some of which may also be useful for Airglow imaging.

Please contact us directly for more up-to-date (and relevant-to-your-project) information.

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Keo Sentry 8 Degree FoV