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. The AO-8 is a replacement for the former AO-7 and can only be used with ST-7/8/9/10/2000 USB cameras.
The unit gets power and commands directly from the camera via a short cable to camera's I2C port. No other external cables are required for power or control. The unit has an I2C output port as well so it is fully compatible with other I2C accessories that you might add to the system, such as a filter wheel or our soon to be released autofocuser.
TIP-TILT HIGH SPEED GUIDING
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 image below shows the AO-L with such an off-axis accessory attached. In this case it is an Astrodon MOAG which allows the Remote Guide Head to be used in front of the filter wheel.
Another benefit of the new AO design is that they take up far less backfocus. The former AO-7 required about 3.5 inches of backfocus and placed the camera at right angles to the optical system. Inserting an off-axis guider or other pick-off mechanism added even more backfocus. However, the AO-L and AO-8 require less than 2 inches of backfocus (when attached directly to the camera) and leave the camera square in the optical path. Additionally, the transmissive element of the new AO design has a relatively large range of motion. In the AO-8 for example, the range of correction is roughly +/- 40 pixels. Assuming one is imaging at approximately 1 arcsecond per pixel, this means the AO-8 can correct for up to about 40 arcseconds of periodic error in the telescope mount. Since most modern mounts with PE error c