Alstar Astronomical 2in M48 Extension Tube Kit - Flexible Spacing

In this review the Alstar Astronomical 2in/M48 extension tube kit is evaluated as a simple, mechanical solution for spacing and focusing tasks in astrophotography. The kit's single biggest advantage is its straightforward, modular approach: each ring has both M48x0.75 male and female threads so multiple lengths can be combined to reach the exact spacing required for cameras, eyepieces, reducers, or field flatteners. It is aimed at hobbyists and amateur astrophotographers who need reliable, metal spacers rather than optical adapters or powered focusers.

Key Features

• M48x0.75 male and female threads: Provides secure, repeatable attachments so components stay aligned when stacking rings.
• Multiple lengths available: Rings in 5mm, 8mm, 10mm, 20mm and 30mm allow precise spacing by combining pieces in various ways.
• All-metal construction: Anodized aluminum construction offers durability and resists wear from repeated assembly and disassembly.
• Simple optical spacing: Eliminates a range of focusing problems by enabling exact backfocus for reducers or flatteners without altering optics.
• Compact 2in format: Works with standard 2in accessories and eyepieces while keeping the optical train rigid.

Who It's For

The kit is best for amateur astronomers and astrophotographers who need to adjust image scale or backfocus with mechanical reliability. If you use reducers, field flatteners, or DSLR/mirrorless cameras on telescopes, the ability to fine tune spacing with discrete metal spacers is highly practical.

It is less suitable for users seeking electronic focuser controls or optical correction - this is a mechanical extension solution rather than an active focusing system. Professionals who require custom CNC-machined adapters or nonstandard threads may also need a different product.

Pros & Cons

Pros

• Modular M48 threading makes achieving precise spacing straightforward and repeatable.
• Durable anodized aluminum construction holds up to regular use and resists wear.
• Range of lengths lets you tune backfocus for a variety of cameras, reducers, and flatteners.

Cons

• Plain extension rings add spacing only and do not provide optical correction or active focusing.
• Users who need nonstandard thread sizes will need an adapter in addition to these rings.

Specifications

Thread (male)	M48x0.75
Thread (female)	M48x0.75
Included lengths	5mm, 8mm, 10mm, 20mm, 30mm
Format	2in extension tube
Material	Anodized aluminum (all metal)
Use	Camera and eyepiece spacing for astrophotography

Our Verdict

The Alstar Astronomical M48 extension tube kit is a practical, low-complexity tool for anyone who must fine tune backfocus in an optical train. Its real strength is modularity and durable metal construction, making it good value for hobbyists who pair cameras, reducers, and eyepieces. Buy it if you want predictable, repeatable spacing without added electronics or optical parts.

Frequently Asked Questions

Can these rings be stacked?
Yes. The M48x0.75 male and female threads allow stacking multiple rings to achieve the required spacing.

Will this change my optics?
No. These are mechanical spacers intended to adjust image scale and backfocus; they do not provide optical correction.

Are they durable for regular use?
Yes. The rings are all-metal with an anodized finish designed to resist wear from repeated assembly.