Porte-oculaires

Manual, Motorized and Robotic Focus

All focusers move a drawtube. What separates them is how much they can hold without slipping and how repeatably they can return to a position.

• Dual-speed manual focusers: Coarse and 10:1 fine focus, entirely adequate for visual observing and for imaging where you are willing to refocus by hand periodically.
• Stepper motor focusers: Absolute positioning with repeatable steps, enabling automated focus routines and per-filter focus offsets.
• Robotic microfocusers: High load capacity with integrated temperature sensing and position feedback, designed for unattended operation across a whole night.
• Load capacity: The specification that matters most for imaging. A camera, filter wheel, off-axis guider and adapters add up quickly, and the load acts as a bending moment when the tube is horizontal.
• Travel and profile height: A replacement focuser with a taller profile can prevent a telescope reaching focus, particularly on Newtonians. This must be checked before purchase.
• Temperature compensation: A sensor and coefficient that shift focus automatically as the tube cools, which removes the largest single source of overnight focus drift.

Why Choose David Astro for Focusers

A focuser is a retrofit, and retrofits fail on details that are easy to check beforehand.

• Focus travel verified: We check that the new focuser's profile still allows your telescope to reach focus with your intended camera or diagonal, which is the most common retrofit failure.
• Adapter identified: We specify the telescope-specific mounting flange alongside the focuser, so the parts arrive complete.
• Load calculated with the moment arm: We consider the weight and its distance from the drawtube, not just the total mass.
• Authorized dealer: Full manufacturer warranty with service handled in Canada.
• Canadian stock: Ships domestically without duties or brokerage fees for Canadian orders.

Focusers in Canada — Frequently Asked Questions

Do I need an electronic focuser?

For imaging below about f/6, yes in practice. Focus shift with temperature exceeds the critical focus zone over a Canadian night, and refocusing manually every hour costs you exposures and disturbs the rig.

Will a new focuser fit my Newtonian?

Only if its profile height is compatible. A taller focuser can push the focal plane beyond the drawtube's inward travel. Tell us the telescope and we will check before you order.

How much load can a focuser really take?

Rated capacities usually assume the tube pointing up. Near the horizon the same weight acts as a bending moment and effective capacity drops. We size with margin for that.

Can I add temperature compensation later?

On most stepper-based systems, yes — a temperature probe and a measured coefficient are all that is required. We can help determine the coefficient for your specific tube.

Replacing a focuser?

Send us your telescope and imaging train weight and we will specify the focuser and flange. Ships from our Canadian warehouse.