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How To Choose The Right Star To Focus


Avid astrophotographer

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:

Hardware requirements:

  • 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.

Software requirements:


  1. Find a suitable star: To do this, perform the following:
    1. Center a magnitude 5 or higher star
    2. 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
    3. 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
    4. Keep moving the focuser and or out until the star is sharp.
    5. 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.
    6. 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.

Video Tutorials

Here are some video tutorials we have of different types of focus in PRISM.

★ Reviews

Let customers speak for us

30 reviews
LE Pyxis

I have received LE Pyxs, very good quality, but does not work with Linux.
But I'm in contact with Optec to get the Linux driver.
We'll see later if it works properly.

Excellent Integrated Package

I bought PRISM v.10 Pro for its integrated capabilities. I did not want to have to "bolt together" different software packages to achieve all my objectives. Two weeks after downloading the software the skies cleared and I was able to use my ZWO CMOS camera and focuser mounted onto a Stellarvue 80mm to move all over the sky finding and taking test shots of Messier objects. I am currently working on deepening my knowledge of what the software can do, particularly pointing models and autoguiding. The look of PRISM is a little outdated - others have mentioned this - but when you discover what you can accomplish with this software package this is easily forgotten. The online tutorials work well to get you off and running and phone support is quite good! I look forward to learning a little bit more each day and to achieving high quality imaging.

Looking forward to trying it!

I bought this in anticipation of using it at my summer home. So it is still unwrapped. It did come highly recommended, and the shipping speed was nothing short of miraculous, so I can't wait to get down to work!

Great device and excellent service.

This is my first experience with Hyperion. I had quick shipping and good service. The eagle is an excellent device for controlling my telescope and camera. It is a powerful pc.

Really does the job...

For those who have the Eagle, the ECCO is a great device to monitor and adjust the dew heater. It is very easy to install. You do a short calibration in the advanced settings, be sure the sensor is properly placed, plug in the cables and bingo--all done. Highly recommend it.