installed EAF and no movement via ZWO ASIAIR Plus

gwzapo

Hello, I have the EAF installed onto my Stellarvue SV80 A refractor. I have ensured that the grub screws are on the flat
surface of the shaft both on the telescope focuser as well as the EAF motor shaft. I'll certainly admit I'm a newbie with regards to the EAF and ASIAIR Plus, I was simply connecting to ASIAIR Plus and doing an initial setup with my wifi and it detected the EAF. I turned on the beep and it beeps once for each touch of the up or down, but no movement. I don't have any cameras installed just yet, just doing an initial setup. Attached is a screen shot showing the default settings.

I am asking to see how I can be sure as to whether or not my EAF is defective.

w7ay

gwzapo I turned on the beep and it beeps once for each touch of the up or down, but no movement.

A couple of things to keep in mind...

Firstly, an EAF button in the ASIAIR are not the kind where it stays activated while you have it pressed down. The EAF makes only a single movement per beep that you hear.

Next, I see that your step sizes are set to 10 (fine) and 30 (coarse). The EAF uses 5760 steps per revolution of its shaft. When attached to the coarse shaft of a typical rack and pinion focuser, each step usually moves the draw tube by about 4 µm (I measured 4 µm on an FSQ-85 and 4.2 µm on a FOA-60Q).

Yes, 4 microns, not a typo -- since critical focusing requires 10 µm to 100 µm of focus delta, depending on f-number of the OTA; better stepper focusers in the market have even finer rotation per step size.

You may simply be stepping but not seeing a 40 µm type movement of your draw tube with your bare eyes. A single beep is a good sign. If there is a snag that prevents the draw tube from moving, you would have heard a double beep.

Try changing the Step Size to about 500 steps per activation, and see if you now see a movement. That will give you a 2mm type movement per button press, which is easily visible. Once you are assured that it is visibly moving, remember to choose a step size that is a factor or 2 or 3 smaller than the critical focus zone (CFZ or NCFZ) of your OTA.

Chen

gwzapo

Thank you for your response. It is exactly what I needed. Sure enough, it moves as it should via the ASIAIR Plus. So I was wondering if there is a way I need to or should try to figure out what parameters should be used for my specific Telescope, the SV80 A Refractor? Thank you again for your quick response and assistance.

Best wishes for a Happy New Year!

w7ay

gwzapo my specific Telescope, the SV80 A Refractor

Easy enough to do: ask the EAF to change by, say 5000 to 10000 steps (in one swoop). Measure the drawtube to see how much it has moved. This tells you how many µm per step. It varies between focusers, but it should be around 2 µm per step to 20 µm per step. (Belt driven helical focusers may be higher resolution, at less than 1 µm per step, depending on the ratio of the pulley and ring gear).

There are web articles on Critical Focus Zone (CFZ or NCFZ) that gives you the equation of the critical focus zone of your particular OTA. (If you are too lazy, there are web calculators.)

Because of Fourier optics ("diffraction limited optics") the focus of a lens does not reach an infinitely small point, but bottoms out to a finite sized Airy point spread function. Inside this "critical focus zone," focusing does not improve or degrade measurably as you change focus.

Once you find the CFZ for your optics, just use the step size that you had measured above to set the focusing steps so that each step corresponds to say, a third or a half of the CFZ. Finer step sizes than that will just be confusing, and a step size larger than one half CFZ will make you miss the true focus point.

HNY 2022 to you too.

Chen