For over 30 years Baader Planetarium have focused on the Astro T-2 thread system (M 42 x 0.75 mm); virtually every telescope manufacturer must offer this thread far ahead of the focal point of his instrument, so that accessories such as a universal T-ring (e.g. for DSLR cameras) can be connected. The only exceptions are (still) Russian equipment, where the thread diameter is the same, but the pitch is still 1mm per revolution – rather than 0.75mm! Therefore, we offer among other things a “Russian adaptor”. At only 7mm additional optical length it can allow so many Russian lenses or telescopes to be compatible with an international Astro T-2 (M 42 x 0.75mm) connector!
To help identify whether threads are internal or external, Baader use lower case letters ‘a’ or ‘i’
- “a”; identifies an external thread (male); or, if Ø sign which a diameter,
- “i”; – a female is always (female) or – Ø character – an inner diameter.
Furthermore Baader also indicates the optical length of their accessories. Optical length describes the extension of the optical path caused by an adaptor or accessory when inserted into the beam path of the telescope. The values listed in the system table rounded to 1/2 mm. For pure threaded adaptors or tubes such as the T-2 ring (#25), the optical length arises directly from its geometric shape. Because the optical design lengths apply to the assembled, external threads are not included in the bill. This explains the extremely short optical length external thread adaptors compared to female threaded adaptors.
Parts that contain optical elements (such as Zenit prisms and binocular) the optical length can vary strongly from the geometrical form of the housing. Hence the values for the optical length by such accessories was determined directly on the telescope. When used with the unique Alan Gee tele-compressor the optical length depends in addition to the distance from the primary focus.
In general: If you add an accessory an item from the Astro T-2 System ™ into the beam path of the telescope, the extension length of the focuser to the value of the specified optical length must be shortened so that the eyepiece tubes moves closer to the lens. For negative values, the focuser must be extended because the distance between the focal plane of the lens increases.
Below is a table of the Baader Astro T-2 system which lists the individual components. Below the table is the Astro T-2 diagram that show how the parts relate to one another.
The Baader Astro T-2 System™ Parts
| T-2 Component # | LABEL (i)=internal THREAD, (a)=external THREAD | Opt. length (mm) | Connection: objective | connection: eyepiece | auxiliary thread or diameter |
|---|---|---|---|---|---|
| # 1A | Maxbright Mirror Diagonal T-2, incl. Adapter #3 | 43 | T-2(i) | T-2(a) | M34(i) out #3 |
| # 1B | T-2 Stardiagonal Prism 90°, 36mm (Zeiss Prism), with male/female T-2 thread, incl. Adapter #3 | 38.5 | T-2(i) | T-2(a) | M34(i) out #3 |
| # 1C | Prism Diagonal T-2 / 90°, 32mm (suitable for Maxbright Bino), incl. Adapter #3 | 35 | T-2(i) | T-2(a) | M34(i) out #3 |
| # 2 | T-2 / 90° Baader Roof-Prism (Astro-Quality-Grade), with male/female T-2 thread, incl. Adapter #3 | 47.5 | T-2(i) | T-2(a) | M34(i) out #3 |
| # 3 | Adapter 36,4a / T-2a (direct T-2 photo-thread for Vixen, NexStar4, Meade a.o. focusers) | 0.5 | M36.4 x 1(a) | T-2(a) | M34(i) |
| # 4A | Glasspath Corrector 1.25 (incl. Teflon-centering) | ≤ -30 | —– | M34(a)/T-2 clamp Ø 38mm | —– |
| # 4B | Glasspath Corrector 1.70 (incl. Teflon-centering) | -65 | —– | M34(a)/T-2 clamp Ø 38mm | —– |
| # 4c | Glasspath Corrector 2.60 (incl. Teflon-centering) | -120 | —– | M34(a)/T-2 Kclamp Ø 38mm | —– |
| # 5 | 1¼” Extension Tube / 1¼” Glasspath Corrector | 18.5 | M28(i) | M28(a) | Ø 26mm(i) |
| # 6 | T-2 Quick Changer (combines Zeiss Micro bajonett with T-2 female thread) Standard Version | 11 | T-2(i) | Ring-clamp | —– |
| # 6A | Baader TQC Heavy Duty T-2 QuickChanger | 11 | T-2(i) | Ring-clamp | —– |
| # 7 | Baader TCR Hardened Steel T-2 ChangeRing | 4 | Ring-clamp | T-2(a) | Ø 38mm |
| # 6+7 | T-2 Changer System (Combination of #6 & #7) | 15 | T-2(i) | T-2(a) | Ring-clamp |
| # 6A+7 | TQC/TCR Heavy Duty Changer System (Combination of #6 & #7) | 15 | T-2(i) | T-2(a) | Ring-clamp |
| # 8 | Click-Lock Eyepiece Clamp 1¼” (with built in diopter-adjustment) | 32-38 | T-2(i) | Ø 1¼”(i) | T-2(a) |
| # 8A | Focusing Eyepiece Holder 1¼”/T-2 with 3 clamping screws Fine focussing (5mm focus travel) Rotation Locking Screw | 29-34 | T-2(i) | Ø 1¼”(i) | —– |
| # 9 | Adapter M44 (i) / T-2 (i) (combo of Zeiss M44 female and T-2 female thread) | 14 | T-2(i) | M44 x 1(i) | Ø 40mm |
| # 10 | Reducer 1¼” / 24.5mm – for 24.5mm eyepieces | 6.5 | Ø 1¼”(a) | Ø 24,5mm(i) | M28,5(i) |
| # 11 | Eyepiece Holder 1¼”/36.4 (a) fits 1¼” oculars onto Vixen thread M36.4 | 27 | M36.4 x 1(a) | Ø 1¼”(i) | —– |
| # 12 | T-2 / M43 x 0.75 Takahashi-Adapter | 0,8 (!) | M43(a) | T-2(a) | M34(i) for #4a,b,c |
| # 13 | External Thread M44(a) / T-2(a) – for Zeiss | 5 | M44 x 1(i) | T-2(a) | Ø 38mm |
| # 14 | Nose piece 1¼”(a) / T-2(a) – with safety groove | 0,5 | Ø 1¼”(a) | T-2(a) | M34(i) / M28,5(i) |
| # 15 | Reducer 2″ / 1¼” – with clamping ring, T-2 thread and M48 filter thread | 9 | Ø 2″(a) | Ø 1¼”(i) | M48(i) / T-2(a/i) / M34(i) |
| # 15A | Pushfix 2″ / 1¼” reducer for Newton focuser | 1 | Ø 2″(a) | Ø 1¼”(i) | M48(i) / T-2(i) |
| # 15B | Baader 2″ to 1¼” ClickLock reducer | 9,5 | Ø 2″(a) | Ø 1¼”(i) | M48(i) / T-2(i) |
| # 16 | Nosepiece connection 2″(a) / T-2(a) and with safety groove. M48 filter thread | 2 | Ø 2″(a) | T-2(a) | M48(i/a) / T-2(i) |
| # 17 | 2″ SC Deluxe eyepiece | 53 | UNC 2″(i) | Ø 2″(i) / S65 | M58(i) |
| # 17A+B | 2″ SC Deluxe eyepiece with 2″ filter holder (for SC & HD) | 53 | UNC 2″(i) | Ø 2″(i) / S65 | 2″ Filter Thread / M58 |
| # 18 | 3.3″ Celestron Nut for C11/C14 (ring clamp #17) | 0 | UNC 3.3″(i) | —– | —– |
| # 19 | 2″ Barrel, chrome, with Teflon spacer rings | 0 | Ø 2″(a) | UNC 2″(a) | M48(i) |
| # 20 | Alan Gee Telecompressor II | ≈≤ 50 | T-2 clamp | T-2 clamp | —– |
| # 21 | Baader T-Adapter (BTA) for all SC and MAK telescopes | 16 | UNC 2″(i) | T-2(a) | T-2(i) |
| # 21 B | SC Ultrashort T-Adapter with a 7mm optical length, T-2 (a) / 2″(i) | 7 | UNC 2″(i) | T-2(a) | T-2(i) |
| # 22 | Thread adapter M43(a) / T-2(a) – Vixen-Adapter | 2,5 | M43 x 1(a) | T-2(a) | Ø 38mm |
| # 23 | Thread adaptor M42x1(i) / T-2(a) – “Russian”-Adapter | 7 | M42 x 1(i) | T-2(a) | Ø 38mm |
| # 24 | T-2 Sliding / Locking Focuser 1¼”(i) and T-2(i) – Hub 11mm | 27.5+11,0 | T-2(i) | T-2(a) | Ø 1¼”(i) |
| # 25A | T-2 intermediate ring 15mm T-2(i) / T-2(a) | 15 | T-2(i) | T-2(a) | Ø 38mm |
| # 25B | T-2 intermediate ring 40mm T-2(i) / T-2(a) | 40 | T-2(i) | T-2(a) | Ø 38mm |
| # 25C | T-2 intermediate ring 7.5mm T-2(i) / T-2(a) | 7.5 | T-2(i) | T-2(a) | Ø 38mm |
| # 25V | Baader VariLock 46 extension Tube 29-46mm with spanner tool | min. 29 / max. 46 | T-2(i) | T-2(a) | T-Adapter |
| # 25Y | Baader VariLock 29 extension tube 20-29mm with spanner tool | min. 20/ max. 29 | T-2(i) | T-2(a) | T-Adapter |
| # 26 | T-2/T-2 Inverter ring – changes T-2(i) in T-2(a) | 0 | T-2(a) | T-2(a) | Ø 38mm |
| # 27 | Thread adaptor 2″(a) / T-2(a) – with M48 thread for 2″ Filter | 0.5 | UNC 2″(a) | T-2(a) | M48(i) |
| # 28 | Expanding ring T-2(i) / 2″(a) | 1 | T-2(i) | Ø 2″(a) | —– |
| # 29 | Threaded ring M48(a) / T-2(i) | 2.5 | T-2(i) | M48(a) | —– |
| # 30 | CCD Collar1¼” (Focus stop ring for CCD cameras, etc.) | ≤ 10 | Ø 1¼”(i) | Ø 1¼”(i) | —– |
| # 31 | T-2 eyepiece filter holder | 0 | T-2(a) | T-2(a) | M28.5(i) |
| # 32 | Eyepiece Ultrashort 2″ (on both sides) for Zeiss (M68) | 17 | M68 x 1 | Ø 2″(i) | M68 x 1 |
| # 33 | Variable extension (12-16mm) incl. lock ring (= #26+34+35) | 12 (10) | T-2(a/i) | T-2(a/i) | —– |
| # 34 | T-2 conversion ring (converts T-2(a) external thread in T-2 (i) internal thread) | 10 | T-2(i) | T-2(i) | —– |
| # 35 | T-2 locking ring | 2 | T-2(i) | T-2(i) | —– |
