Operating Manual CCD Camera Models ST-7E, ST-8E, ST-9E, ST-10E, ST-1001E

Section 3 - At the Telescope with a CCD Camera

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Another aspect of the Focus command and its various modes is the Camera Resolution

setting in the Camera Setup command. Briefly, the Resolution setting allows trading off image

resolution (pixel size) and image capture time while field of view is preserved. High resolution

with smaller pixels takes longer to digitize and download than Low resolution with larger

pixels. The cameras support High, Medium, Low and Auto resolution modes. The Auto mode

is optimized for the Focus command. It automatically switches between Low resolution for

Full frame mode to provide fast image acquisition, and High resolution for Planet mode to

achieve critical focus. While Auto resolution is selected all images acquired using the GRAB

command will be high resolution.

3.9.3. Track and Accumulate

An automatic Track and Accumulate mode (SBIG patented) is available in CCDOPS which

simplifies image acquisition for the typical amateur with an accurate modern drive. These

drives, employing PEC or PPEC technology and accurate gears, only need adjustment every 30

to 120 seconds. With Track and Accumulate the software takes multiple exposures and

automatically co-registers and co-adds them. The individual exposures are short enough such

that drive errors are not objectionable and the accumulated image has enough integrated

exposure to yield a good signal to noise ratio.

Operationally the camera will take an exposure, determine the position of a preselected

star, co-register and co-add the image to the previous image, and then start the cycle over

again. Up to 64 images can be co-added, and the software even allows making telescope

corrections between images to keep the object positioned in the field of view. The resulting

exposure is almost as good as a single long exposure, depending on the exposure used and sky

conditions. The great sensitivity of the CCD virtually guarantees that there will be a usable

guide star within the imaging CCD's field of view. This feature provides dramatic

performance for the amateur, enabling long exposures with minimal setup!

3.9.4. Autoguiding and Self Guiding

The CCDOPS software allows the ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E cameras to be

used as autoguiders and self-guiders (except the ST-1001E) through the commands in the Track

menu. While these systems are not stand-alone like the ST-4, but require a host computer, they

can accurately guide long duration astrophotographs and CCD images with equal accuracy.

Their sensitivity is much greater than an ST-4, and the video display easier to use.

When functioning as an autoguider, the CCD camera repeatedly takes images of a

guide star, measures the star's position to a fraction of a pixel accuracy, and corrects the

telescope's position through the hand controller. While autoguiding alleviates the user of the

tedious task of staring through an eyepiece for hours at a time, it is by no means a cure to

telescope drive performance. All the things that were important for good manually guided

exposures still exist, including a good polar alignment, rigid tubes that are free of flexure and a

fairly good stable mount and drive corrector. Remember that the function of an auto guider is

to correct for the small drive errors and long term drift, not to slew the telescope.

The Resolution setting in the Camera Setup command combines pixels before they are digitized.

This is referred to as on-chip binning and offers increases in frame digitization rates.