How to choose a good star for focus?
Choosing the right magnitude star to focus on is a critical part of a successful autofocus run. Automatic observation relies heavily on acquiring sharp images all night long to accumulate as much data as possible.
Things to consider:
- A focuser
- A motor to move the focuser in and out
- A good driver( preferably ASCOM compliant)
- No Mirror flop: Some moving mirrors offer some great challenges to a successful autofocus run.
- Find a suitable star: To do this, perform the following:
- Center a magnitude 5 or higher star
- Make sure it is centered: Some fields are quite curved and the best place is to have the star in the center of the image
- If the star is defocused, use the manual focus tool to render the image as sharp as possible by using this function: Observatory > Focusing > Manual Focus
- Keep moving the focuser and or out until the star is sharp.
- Now it is time to identify is the chosen star saturates at the exposure time and binning you chose. Go to Image Display > Show Saturated Pixels.
- This window pop up:
7. Choose the right bit depth for your camera, here are some examples:
QSI583 = 16bit
ZWO ASI1600 = 12bit
SBIG STL11000 = 16bit
8.If the star is saturated, PRISM will display all the saturated pixels as such:
9. Repeat the process until you find a suitable star for your system.
Here are some video tutorials we have of different types of focus in PRISM.