SVBONY SV135 1.25″ 7–21mm 57°–40° Zoom Eyepiece

Product Overview

The SVBONY SV135 is a 1.25″ zoom eyepiece that covers 7 mm to 21 mm with a twist of the barrel, giving a 57° apparent field at the short end and 40° at the long end. It uses a fully multi-coated 4-group, 6-element design, keeps 16.3–18 mm of eye relief across the range, and has an M28.5 × 0.6 thread for 1.25″ filters. It is 93 mm long and weighs 133 g.

Who It's For

This is a good match if you want one eyepiece that covers the most-used magnification range in a 1.25″ focuser — framing a target at 21 mm, then zooming in to 7 mm when the seeing allows — for the Moon, planets, double stars and star clusters. The 16.3–18 mm eye relief suits observers who keep their glasses on.

Key Features & Design

• 7–21 mm linear zoom: continuous magnification change without swapping eyepieces.
• 57°–40° apparent field: widest at 7 mm, where a wider field helps keep planets in view on an undriven mount.
• 16.3–18 mm eye relief: comfortable with or without eyeglasses.
• Fully multi-coated optics: 4 groups, 6 elements.
• Aluminium housing with rubberized collar: non-slip grip, including in the cold or with gloves.
• M28.5 × 0.6 filter thread: takes SVBONY and other standard 1.25″ filters.

Optical Design

The SV135 is a linear zoom: the focal length changes in proportion to the barrel rotation, with six elements in four groups and full multi-coating on the air-glass surfaces. As in most zooms, the apparent field narrows as focal length increases — here from 57° at 7 mm to 40° at 21 mm — while eye relief stays between 16.3 mm and 18 mm. On a 1000 mm focal-length telescope, the range works out to roughly 48× to 143×.

Recommended Uses

• Planetary observing: zoom in to match the seeing on Jupiter, Saturn and Mars.
• Lunar observing: move from whole-disc views to crater detail.
• Star clusters and double stars: frame at 21 mm, then tighten.
• Outreach and travel kits: one eyepiece in place of three or four.

Compatibility and Accessory Notes

• Barrel: 1.25″, fits standard 1.25″ focusers and diagonals.
• Filters: M28.5 × 0.6 thread for SVBONY 1.25″ filters.
• Bundles: SVBONY also offers this eyepiece in bundles with the SV188P and other accessories; contact us if you would like one of those combinations.

Good to Know Before You Order

• Field narrows with focal length: 40° at 21 mm is narrower than a fixed wide-field eyepiece of the same focal length.
• 1.25″ only: there is no 2″ barrel.
• Three SV135 versions: SVBONY sells 52°–36°, 57°–40° (this one) and 60°–40° versions with different optical designs and weights.

Frequently Asked Questions

Is it difficult to set up?

No. It drops into a 1.25″ focuser or diagonal like any eyepiece; twist the barrel to zoom and refocus as needed.

Can I use it for astrophotography?

It is a visual eyepiece. It can be used for simple eyepiece-projection or smartphone shots, but its main purpose is observing.

What magnification will I get?

Divide your telescope's focal length by 7 and by 21. On a 1000 mm telescope that is about 143× at 7 mm and 48× at 21 mm.

How does it differ from the other SV135 versions?

This version has a 4-group, 6-element design with a 57°–40° field and 16.3–18 mm eye relief; the 52°–36° version uses 3 groups/5 elements and the 60°–40° version 4 groups/7 elements.

Bottom Line

In short: a 133 g, 1.25″ zoom eyepiece covering 7–21 mm with a 57°–40° field and 16.3–18 mm eye relief — a single eyepiece for lunar, planetary and cluster observing.