High-quality telescope focusers are essential to achieve perfect focus, whether you use your telescope for astrophotography or visual observation. To help users upgrade their focusing performance, PrimaLuceLab developed two advanced motorized solutions: SESTO SENSO 3, our robotic focusing motor that enhances the telescope’s existing focuser, and ESATTO, our complete robotic focuser that replaces the stock unit with a high-precision, high-load-capacity system. While both families share the same premium electronics and control ecosystem, they differ in mechanical design and capabilities — making each one ideal for specific telescopes and applications. In this article, you’ll learn how the SESTO SENSO 3 and ESATTO compare, and how to choose the best motorized telescope focusers for your setup.
SESTO SENSO 3 and ESATTO: shared technologies
All SESTO SENSO 3 and ESATTO models share the same advanced PrimaLuceLab electronics and controls:
- USB-C port for direct connection to EAGLE or any external computer
- Wi-Fi connectivity for wireless control with the included Virtual HandPad
- Port for ARCO camera rotator and field de-rotator
- Temperature probe port for automated temperature-compensated focusing
- Dimmable status LEDs
- Full compatibility with PLAY astrophotography software and ASCOM drivers
Both systems provide high focusing precision, and both support automatic and remote focusing. Where they differ is in their mechanical concept.
SESTO SENSO 3: a focusing motor for your external focuser
SESTO SENSO 3 is a telescope focusing motor designed to be installed on the fine focus shaft of your rack-and-pinion or Crayford-style focusers. This makes it the ideal solution when your telescope already includes a high-quality, smooth, dual-speed focuser.
When SESTO SENSO 3 is the best choice:
• Refractors or Newtonians with quality Crayford or rack-and-pinion focusers
• Telescopes used both for visual and astrophotography
• Users who want a motorized solution that is non-invasive and affordable
Key advantages
• Non-invasive installation — no need to replace the focuser
• Integrated encoder: while the motor is ON, you can move the focuser knob manually without losing calibration
• Perfect for switching quickly between eyepieces and cameras
• Light, compact, and cost-effective
Limitations
Since SESTO SENSO 3 controls the existing focuser, it cannot correct mechanical issues such as:
• Backlash
• Flexure or limited load capacity
• Image shift caused by the primary mirror (in SCTs or similar designs)
If your focuser has one of these limitations, upgrading to ESATTO is recommended.
SESTO SENSO 3 SC for Schmidt-Cassegrain and similar telescopes
For Schmidt-Cassegrain, ACF, EdgeHD, or Maksutov telescopes equipped with internal focuser, we developed the SESTO SENSO 3 SC — a dedicated version that connects directly to the telescope’s focusing knob.
Advantages of SESTO SENSO 3 SC:
• Motorizes the native focuser
• Still allows manual focusing when needed
• Non-invasive, quick to install
• Great for users who want a simple solution for visual and imaging without adding backfocus
However, like any motor that drives the original internal mechanism, it cannot eliminate mirror shift. If mirror shift is a concern, ESATTO is the superior solution.
ESATTO: a complete robotic focuser
ESATTO is a complete robotic focuser that replaces the original focuser (or is added to telescopes with internal focuser). It combines precision mechanics, high-load-capacity, motor, and control electronics in all in one compact, integrated unit. ESATTO is available in many versions:
• ESATTO 2”, 3”, 4”
• ESATTO 2” LP, and ESATTO 3.5” LP – Low Profile versions
When ESATTO is the best choice:
• When your stock focuser has backlash, flexure, or limited load capacity
• When using heavy cameras, filter wheels, and accessories
• For demanding astrophotography setups
Advantages of ESATTO
• Ultra-precise movement
• High load capacity (from 5kg to 10kg depending on the model)
• Larger free apertures also for full-frame or larger sensors
• Available in Low Profile versions for reducers / flatteners
This is perfect for fine focusing and automated imaging. Being a complete robotic focuser, ESATTO is naturally less affordable than SESTO SENSO 3, and it also requires a dedicated adapter to be installed on each telescope model, since every telescope features a different mechanical interface. However, ESATTO provides higher performance compared to SESTO SENSO — with greater mechanical precision, higher load capacity, and improved rigidity — making it the ideal choice for demanding astrophotography setups.
Which motorized telescope focuser should you choose?
Choose SESTO SENSO 3 if:
• Your refractor or Newtonian telescope already has a high-quality focuser
• You want a non-invasive, affordable motorized solution
• You use your telescope both visually and for imaging
Choose SESTO SENSO 3 SC if:
• You have a Schmidt-Cassegrain or similar telescope
• You want a simple, non-invasive motorization
• Mirror shift is not a major concern
Choose ESATTO if:
• Your current focuser has backlash, flexure, or limited load capacity
• You use heavy cameras and accessories and you need the highest performance for astrophotography
• You want to eliminate mirror shift on SCTs with mirror lock
Conclusion
SESTO SENSO 3 and ESATTO are among the most advanced motorized telescope focusers available today, designed to greatly enhance the precision, stability, and control of your telescope’s focusing system. The best choice depends on your telescope type, the mechanical quality of its existing focuser, and your observing or imaging goals. By selecting the right telescope focuser — SESTO SENSO 3 to upgrade a high-quality manual focuser, or ESATTO for maximum performance with a complete robotic focuser — you can unlock the full potential of your telescope. You’ll achieve precise, repeatable, and even fully automated focusing: a key advantage for high-level astrophotography and an important improvement for visual observation as well.