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Focus Motor Comparison: ZWO EAF vs Primaluce Labs Sesto Senso 2

Telescope focused with Sesto Senso 2 and stock rack & pinion focuser. Credit: Rouzbeh Bidshahri

Precision focusing is one of the most critical factors for getting crisp images. Most modern imaging software now features autofocus routines that, with the use of a motorized focuser, can automatically determine the optimal focus point.

Two of the most popular focus motors are the ZWO EAF and the Primaluce Labs Sesto Senso 2. Both of these motors attach to your existing focuser to enable software automation and control.

We will compare these motors side-by-side so you can determine which is most suitable for you.

Dual telescope setup, ZWO EAF on left telescope – Primaluce Labs Sesto Senso 2 on right. Credit: Rouzbeh Bidshahri

Price

Both of these focus motors are reasonably priced. The ZWO EAF motor costs $199, with additional accessories sold separately like the hand controller, temperature probe, and optional brackets needed for Takahashi and SCTs (they cost about $30).

The Primaluce Sesto Senso 2 costs more at $299 for the motor, with the temperature probe separately as well. The motor attaches to many standard 25mm (outer ring) focusers without requiring additional brackets, but larger focusers will need brackets that are relatively expensive at $76 and up.

Sesto Senso 2 attached to a standard sized focuser. Credit: Rouzbeh Bidshahri

Weight and Size

Both focusers are reasonably small, with the ZWO EAF being lighter of the two at 277 grams, and physically smaller as well.

The Sesto Senso is larger and heavier at 380 grams. The CNC finished body does feel more substantial, though.

Installation

Both are relatively easy to attach with included flexible couplings to compensate for minor alignment imperfections (the older Sesto Senso 1 didn’t have these flexible couplings). There are several sizes of couplers included with both motors for various shafts. The designs of the two motors are quite different, though.



ZWO EAF:

The ZWO EAF has its own internal gears, meaning it doesn’t utilize your focuser’s reduction, attaching to coarse focus shaft.

The ZWO EAF is simpler to connect as it only requires a USB 2.0 cable to power and control it.

The EAF uses a universal bracket to attach to the housing of the focuser rather than the reduction outer ring.

ZWO EAF and bracket mounted on the focuser housing and connected to the coarse focus side, not the fine focus one. Credit: Rouzbeh Bidshahri

Primaluce Labs Sesto Senso 2:

The Sesto Senso uses your focuser’s own gear reduction, which is usually friction-driven. This means you have to attach it to the fine focus shaft of your focuser.

Fine focus shaft with the Sesto Senso 2 adapter. Credit: Rouzbeh Bidshahri

After removing the fine focus knob, the motor has a clamp that tightens around the outer ring of the focuser reduction mechanism. Besides the USB-C cable, the Sesto Senso requires additional 12v power, for which a cigarette plug type cable is supplied (the larger 5.5×2.5mm plug, not the more common 5x5x2.1mm).

Sesto Senso 2 layout. Credit: Rouzbeh Bidshahri

Software

Both motors are ASCOM compatible.

ZWO EAF:

The ZWO EAF has a very simple software interface and almost no setup.

You simply connect to the motor and can set the current position to “0” when the focuser is fully retracted. You can then set a maximum limit for it to stop at.

The motor will connect and run without any settings; the hand controller is a simple push button device connected by a wire. If you opt to use the hand controller, you can no longer use the external temperature probe, though.

Simple setup tab of the ZWO EAF. Credit: ZWO

Primaluce Labs Sesto Senso 2:

The Sesto Senso uses its new “Play” software. It’s a full package that controls all the different accessories in the Primaluce Lab ecosystem. The version I used had issues connecting and the whole process was more work than I preferred. I missed the older interface that I found more straightforward.

The first time it’s connected, the position has to be calibrated from fully in to fully out to set the limits.



What I did like was the ability to alter the speed settings of the motor, as well as the current.

There is an app to allow you to use your phone as hand controller via Wi-Fi. Again, it’s a bit more work, and visual users might prefer a good old fashioned paddle hand controller without a bright screen.

Primaluce Labs Play interface. Credit: Rouzbeh Bidshahri

Performance

Speed:

Although though both focus motors look somewhat similar, the performance difference is substantial.

First off, the raw speed and power of the Sesto Senso is a lot more than that of the EAF. At full power and speed settings, the Sesto could fully retract my 3.2 inch FeatherTouch with a heavy imaging train in a matter of seconds.

The EAF, not using 12v power, will take much longer to move the same distance.

Payload:

ZWO states the EAF’s capacity is 5kg (11lbs). I couldn’t find a stated capacity for the Sesto Senso, but I believe it has a significantly higher payload capacity compared to the EAF. That is expected given the motor is much larger and runs on higher voltage.

As the EAF has an internal gearbox, it does not require current to hold the position of the focuser under load; the motor shaft can’t be forced to rotate. I suspect it uses less power as well.

The Sesto, on the other hand, requires constant current to hold it in place. Heavy cameras would require more current to hold the motor position.

Resolution:

ZWO published the EAF resolution as 5,760 steps per 360 degrees (one revolution). Primaluce Labs note 0.7 microns per step. That’s linear motion in combination of the focuser so a direct comparison isn’t possible, but I noticed it takes a lot more steps to move the same amount with the Sesto, indicating it has a higher resolution.

Backlash:

This was where I noticed the largest performance difference.

The ZWO EAF has significant backlash. I could even feel the shaft backlash when trying to turn the shaft back and forth with my fingers. That is the nature of meshed gears. You can set backlash compensation in the software though.

The Sesto Senso has no backlash. The output shaft comes directly from the motor with no gears in the way. The reduction gears on the focuser are friction based so they too don’t introduce backlash. If you have a Crayford (friction drive mechanism) then the system could be backlash-free (as with my hi-resolution planetary setup).

Sesto Senso 2 paired with the friction drive 2-inch FeatherTouch Crayford focuser. Credit: Rouzbeh Bidshahri

Final Thoughts

Both focus motors would be suitable for imaging and autofocus routines.

The Primaluce Labs Sesto Senso would get the nod for quality and performance. The ZWO EAF is easier to use, especially when considering the software, and costs significantly less.

It comes down to the user’s requirements. I used the EAF for simple setups but preferred the Sesto Senso for situations that required higher precision.

Sesto Senso 2 Advantages

  • No backlash
  • Higher precision and resolution
  • Higher speed and capacity

ZWO EAF Advantages

  • Lower cost
  • No 12v power required – 1 x USB cable only
  • Brackets are cheaper
  • Almost plug and play software

Websites:

ZWO: https://astronomy-imaging-camera.com/

Primaluce Labs: https://www.primalucelab.us/

MSRP:

ZWO EAF: $199

Sesto Senso 2: $299

 

Author’s gallery with more example: https://www.astrobin.com/users/Rouzbeh/

About Rouzbeh Bidshahri

Rouzbeh Bidshahri is a mechanical engineer with a lifelong passion for astrophotography. He has tested dozens of telescopes ranging from 3 to 20 inches in aperture and has spent several years optimizing systems for very high-resolution planetary imaging in the sub 0.1 arcsecond/pixel range. He has contributed to several institutions such as ALPO (The Association of Lunar and Planetary Observers). His main area of interest has been designing and operating larger setups, and he is currently focusing on high resolution, long exposure photography for both broadband and narrowband deep sky imaging.

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