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
Adaptors T-2 to 1.25 nosepiece
$ 19.90

Omegon
Camera adaptor T2-Ring für Nikon
$ 19.90

Omegon
Camera adapter 1.25"
$ 24.90

Omegon
Syncfocus flip-mirror (for planetary cameras)
$ 69.00

Omegon
M43 / T2 T-adapter
$ 19.90

Omegon
flip mirror
$ 119.00

Meade
Photo adapter #64ST for ETX-70/80
$ 38.90

Omegon
Adaptors 1.25'', 30mm extension tube
$ 24.90

Celestron
T-adapter for C5, 6, 8, 9.25, 11, 14
$ 32.90

Omegon
Cronus T2 Adapter
$ 24.90

William Optics
Camera adaptor T-Ring Nikon Z 48mm
$ 84.00

Omegon
SCT Adapter, ultrashort, T2 (male) / 2''
$ 34.90

Omegon
M48/T2 adapter – short version
$ 14.90

ZWO
Canon EOS adapter for ASI cameras
$ 110.00

ZWO
Camera tripod adapter for cooled ASI cameras 78mm
$ 88.00

Omegon
T2 ring for Minolta AF and Sony A-Mount cameras
$ 29.90

Omegon
Adaptors C-mount to 1.25'' adapter ring
$ 11.90

William Optics
Camera adaptor M48 compatible with Canon EOS
$ 66.00

Omegon
CS to C-mount adapter
$ 9.90

Omegon
Nosepiece 2” ver 1 (M42 to 2”)
$ 24.90

Baader
Hyperion T-adapter M43/T-2
$ 27.90

Omegon
T2 adapter for Canon EOS lenses
$ 99.00

Omegon
C-mount male to T2 adapter female
$ 24.90

Baader
Camera adaptor T2/Fuji x-Mount & S52 Wide-T
$ 42.90

Celestron
Camera adaptor T2 ring for Canon EOS and ZenithStar 71/61 field flattener
$ 32.90

Omegon
Adapter T2 male to T2 male
$ 19.90

William Optics
Adaptors M48 / Sony E
$ 77.00

Bresser
Camera adaptor T2 ring compatible with Canon EOS R/RP Wide-T
$ 27.90

Omegon
M54 / T2 T-adapter
$ 24.90

ZWO
Nikon lens adapter for ASI cameras
$ 94.00

Omegon
Adapter M48 male to T2-thead ring female
$ 24.90

Bresser
Camera adaptor M48 compatible with Canon EOS R/RP
$ 27.90

Explore Scientific
Camera adaptor M48 compatible with Canon EOS
$ 28.90

ASToptics
M48 to 1.25" adapter
$ 22.90

Bresser
SC/T2 CCD adapter
$ 32.90
