SVBONY SV221 1.25″ 45° Erect-Image Prism Diagonal

Product Overview

The SVBONY SV221 is a 1.25″ prism diagonal that turns the light path through 45° and delivers an erect, non-reversed image – right-side-up and correct left-to-right. It has a 19 mm clear aperture, a multi-coated prism and an optical length of about 86 mm. The housing combines ABS with aluminium end barrels, the nosepiece carries an M28.5 x 0.6 filter thread, the eyepiece holder clamps by screw with a brass compression ring, and the diagonal weighs 79 g (2.78 oz).

Who It's For

This is a good match if you use a refractor or a Maksutov or Schmidt-Cassegrain for both daytime terrestrial viewing and night-sky observing and want an image that matches what you see with your eyes, at a comfortable 45° viewing angle.

Key Features & Design

• Erect, non-reversed image: correct orientation for terrestrial targets and easier star-hopping with a printed chart.
• 45° deflection: a natural angle for viewing objects low on the horizon and land targets.
• Multi-coated prism: SVBONY specifies higher light transmission.
• Filter thread: M28.5 x 0.6 inside the nosepiece for 1.25″ filters, with internal blackening.
• Brass compression ring: brass locking screws and ring protect eyepiece and barrel finishes.

Recommended Uses

• Lunar and planetary observing, which SVBONY lists as its main night-sky use.
• Terrestrial viewing and birding through a small refractor.
• Public outreach and casual sessions, where an upright image is easier for everyone at the eyepiece.

Compatibility and Accessory Notes

• Telescopes: refractors and catadioptrics such as Schmidt-Cassegrain and Maksutov-Cassegrain telescopes with a 1.25″ visual back.
• Eyepieces: any 1.25″ eyepiece.
• Filters: M28.5 x 0.6 thread on the nosepiece.
• Newtonians and Dobsonians: these do not use a diagonal, and SVBONY does not recommend the SV221 for them.

What's in the Box

• 1 x SV221 1.25″ 45° correct-image prism diagonal
• 3 x M3 screws
• 1 x dust cap
• 1 x dust plug

Good to Know Before You Order

• 1.25″ only: the barrel and eyepiece holder take 1.25″ accessories.
• Optical length about 86 mm: if your telescope has limited inward focus travel, send us the model and we will confirm it reaches focus with this diagonal.

Frequently Asked Questions

Is it difficult to set up?

No. It slides into the telescope's 1.25″ focuser or visual back and the eyepiece locks into it with the thumbscrew.

What does erect image mean?

The view is right-side-up and not mirror-reversed, the same orientation you see with your eyes.

Can I use it at night?

Yes. SVBONY lists it for Moon and planet viewing, alongside daytime targets.

Will it work on my Newtonian?

Newtonian and Dobsonian telescopes do not use a diagonal, so it is not intended for them.

Bottom Line

In short: a 79 g, 1.25″ 45° prism diagonal with an erect, non-reversed image and filter threads for refractors and catadioptric telescopes used both day and night.