Santa Barbara Scientific SM-4 Seeing Monitor

Imaging System and Optics

At the core of the SM-4 is the QHY5III462M CMOS camera, which features exceptionally high quantum efficiency (approximately 90 percent) and ultra-low read noise in the range of 1 to 3 electrons. This camera is paired with a Kowa 100 mm f/2.8 C-mount lens, a high-quality Japanese optic known for sharpness and mechanical stability. Together, they capture 0.01-second exposures with sub-pixel centroid accuracy, making the system well suited for tracking subtle atmospheric distortions.

Enclosure and Mounting

The SM-4 is enclosed in a weather-resistant aluminum housing with an optical-grade protective window. The design is intended for permanent outdoor installation. The lens can be focused manually, and fine pointing adjustments are made without moving the main enclosure. A USB 3.0 connection ensures fast data transfer to a connected PC. The overall design eliminates the need for telescope mounts or automated domes.

SIMM Method and Data Collection

Rather than relying on traditional Differential Image Motion Monitor (DIMM) techniques, which require a dual-aperture mask and moving telescope, the SM-4 uses a Single Image Motion Monitor (SIMM) approach. It continuously images Polaris, calculating the root mean square (RMS) motion of the star’s centroid over a set of 256 frames. This process takes about one minute and avoids mechanical tracking errors and internal tube currents.

The custom software developed by Dr. Alan Holmes corrects for Polaris’s slow drift across the field during the night and converts measurements to zenith FWHM seeing values using standard atmospheric models. Results are displayed in real time and logged to text files every five minutes in the SeeingMonitor directory. A live graph of the last 12 hours is updated continuously and can be accessed or posted to a website if needed.

SM-4 EX Model for Remote Installations

For installations where the monitor must be located far from the control computer, the SM-4 EX model integrates a USB 3.0 extender over Ethernet. This version includes a USB-to-Ethernet transmitter, a power supply, and an Ethernet-to-USB receiver unit built directly into the enclosure. The user provides a Cat6, Cat7, or Cat8 Ethernet cable of the required length. The system has been successfully tested up to 150 feet with Cat6 cable, providing reliable remote operation without signal degradation.

Use Cases and Application

The SM-4 is ideal for permanent observatories, research facilities, and advanced amateur astronomers who need accurate and repeatable seeing data. It is equally valuable for mobile setups, helping to decide when to attempt long-exposure, high-resolution imaging and when to switch to wide-field or narrowband work. The seeing monitor identifies trends in atmospheric stability that are often missed by visual inspection alone or weather forecasts.