The world of adapters is diverse and not easy to understand. This is due to the wide variety of thread and plug sizes that optics and accessories may have.
In astronomy, two plug sizes have become established, which are often indicated in the old unit inches ("):
- 1.25" corresponds to 31.8 millimetre
- 2" corresponds to 50.8 millimetres
Many eyepieces, but also cameras, have connectors in one of these two sizes, which can be inserted into the telescope’s focuser.
If a 1.25" connector is to be inserted in a focuser with a 2" connector, a 1.25"/2" adapter is required. This is an example of a reducer adapter: where a connection is reduced from a larger size to a smaller one. The reverse is called an extension adapter.
Another very important category of adapters is camera adapters. These are used to connect cameras to optics or to accessories. The T2 thread (M42x0.75), which enables a screw connection, is very well established for this purpose. Lighter cameras without many accessories can also be easily connected to the telescope via a socket.
For astrophotography it is important that the aperture is large enough to illuminate the sensor (no vignetting) and the optical length matches the focal point.

Omegon
2“ Extension tube, 35mm optical path
$ 29.90

Omegon
2'' - 1.25'' Twist-lock adapter
$ 79.00

Omegon
2'' extension tube with 50mm optical path
$ 39.90

Omegon
1.25'', 30mm extension tube
$ 19.90

Omegon
2'' extension tube, 80mm optical path
$ 49.90

Explore Scientific
Extension tube M48 set
$ 60.00

Omegon
2'' Twist-lock adapter
$ 99.00

ASToptics
Extension tube M48 Fine tuning Kit - 0.5mm; 0.8mm; 1mm
$ 26.90

Omegon
Extension tube 45mm Extender 2''
$ 29.90

Omegon
40mm T2i/T2a T2 extension ring
$ 24.90

Baader
ClickLock 2" to 1.25" reducer adapter
$ 90.00

ASToptics
Extension Tube M48 Filter thread - 4mm Length
$ 21.90

PegasusAstro
Adapter M54 Male - M54 Male
$ 32.90

Omegon
T2 extension tube - 30mm
$ 19.90

ZWO
T2 / C mount adapter
$ 26.90

Baader
T2/1.25" ultrashort adapter
$ 34.90

Omegon
T-Adapter M54(m)/T2(m)
$ 24.90

Omegon
2'' adapters with reducer 1.25 ''
$ 29.90

Omegon
7.5 mm T2i/T2a T2 extension ring
$ 19.90

ASToptics
M42 (FEMALE) TO M42 (FEMALE) adapter, 10MM
$ 26.90

iOptron
iPolar adapter for CGEM/EQ6/AZ-EQ6
RRP:
$ 64.00
Our price:
$ 62.00

Artesky
Adapter Twist Lock 2" (Skywatcher Newton)
$ 109.00

Baader
Adapter 2" M54 ClickLock clamp
$ 96.00

Howie Glatter
Parallizer 2" to 1.25" reducer adapter
$ 215.00

ASToptics
Extension tube M48 - Filter thread - 5mm long
$ 21.90

Baader
Extension tube Hyperion Finetuning ring 14mm
$ 22.90

ASToptics
M48(M) to 1.25" filter(F) adapter
$ 16.90

Baader
Extension tube Hypoerion Finetuning ring 28mm
$ 24.90

Omegon
2" extension tube
$ 19.90

Omegon
2'' to 1.25" reducer adapter
$ 39.90

Omegon
15mm T2i/T2a T2 extension ring
$ 24.90

Omegon
Extension tube Extender 30 mm T- thread
$ 29.90

ZWO
M54 Adapter für Filterschublade
$ 37.90

ASToptics
1.25" eyepiece to 0.965 focuser adapter
$ 37.90

ASToptics
M54*0.75 - 5MM extension ring
$ 32.90
