The AO-8 is a second generation adaptive optics system from SBIG specifically designed to enable an SBIG camera user to obtain the ultimate in image resolution that his/her telescope and site can achieve.

SBIG has exploited the second guiding CCD detector in our self-guiding cameras to stabilize stellar images, enhancing resolution. These new AO systems use a tip-tilt transmissive element to correct for image wander due to low order local atmospheric effects and for correction of mount errors, wind vibration and other erratic motion of the optical system that is otherwise too fast for an autoguider or telescope drive corrector to respond to effectively. By monitoring a guide star with the smaller tracking CCD that is built-in to SBIG cameras, or the Remote Guide Head, the AO makes fine corrections at approximately 10 times per second to hold the image fixed on the CCD during the exposure.

The system is closed loop, which means that it checks the position of the guide star after every move and makes adjustments on the next move. This results in a series of small, fast and very precise moves that continue over the course of a long exposure. This is possible because the guide chip is located behind the AO device and can measure the results of each move it makes. In the past, with the AO-7, this presented some difficulties when using narrow band filters because light from potential guide star candidates was attenuated by the narrow band filter to one degree or another resulting is guide stars that could be difficult to find or too dim to use. However, the new AO design and new camera improvements eliminate this problem. Because of their more compact design, the new AO systems lend themselves to the use of off-axis guiders that can place a pick-off mirror or diagonal in front of the filter wheel. Also, all new USB cameras support a Remote Guide Head that essentially places the on-board guiding CCD anywhere in front of the filter wheel the user decides and this Remote Guider duplicates all the functions of the built-in tracking CCD, including the fast readout function required to control the AO. This means that by using a custom off-axis guider, one can still have all of the benefit of the AO no matter what filter is being used, even filters that make starlight nearly invisible to the imaging CCD.

The results one can achieve with the AO-8 depends on a number of factors and no two imaging sites are exactly the same. However, many years of experience with the former AO-7 and now the AO-L make it clear that SBIG's implementation and design of a closed loop AO offers a distinct advantage in image resolution, even when one has superior optics, mount and calm seeing. Take for example the test images below of the same double star captured with and without the AO-L operating. The brighter star is approximately mag 14.7 and the dimmer star is approximately mag 15.7. Separation is approximately 3.7". Two 15 minute images were taken one right after the other on the same night with an STL-11000M-C1 camera through a 20" F/8.3 RC scope mounted on a Paramount. The AO-L image clearly shows a tighter, brighter, better resolved stars compared to the non-AO image. The AO improved the measured FWHM (Full Width at Half-Maximum) and peak brightness of both stars by nearly 30%.