I recently added a particularly geeky new accessory to my astrophotography setup: a computer controlled focusing motor.
Why would someone need such a thing? Well there is one big reason: being in focus as possible is the one thing that trumps everything else in your astrohphoto! Either it’s crisp and sharp as seeing will allow or it’s flawed from the start with no recourse.
The problem is that without some kinds of hands-off control the act of touching the focuser with your fingers in order to turn it shakes the telescope and mount juuuuuust enough so that you can’t really tell if your focus is improved or worsened until it settles down. So wouldn’t it be great if you could adjust focus without touching it?
Enter the ZWO “EAF” (Electronic Auto-Focuser). using a mounting bracket they provide you remove one of your focusing knobs and use a coupler to attach the motor to the shaft of the focuser that can be controlled by control software to achieve perfect, shake-free focus for your photos. It takes the entire travel of your focuser and breaks it up into individual steps, 12, 800 of them on my 100mm refractor. This way you have a numerically absolute point of focus, or at least a good place to start since there are a few small variables when it comes to the act of focusing.
The same iPad app I use to control my cameras and adjust the precise pointing of the telescope mount can also control the focuser and the position of the focuser can now be numerically described and written into the meta-data of the image itself..
One thing I didn’t know until looking more deeply at this aspect of astrophotography is that focus can change with ambient temperature. It can take hours to take certain kind of photos; my ‘deepest’ exposure is two hours and that’s just a wink compared to what the professionals are into. So if you take an “all-nighter” of 6 hours the temperature could change 10 or 15 degrees so the autofocuser comes with a temperature sensor which can also end up in the meta-data. I’m still figuring out how I’ll put this knowledge to use but at least it’s available.
I made a two minute “getting to know you” video showing it in operation…