Introduction
After I bought a Borg helical focuser to use with my 4″ Mak I noticed that my other Sky-Watcher ‘scopes also have T-threads (M42x0.75) and/or “small Vixen” threads (M36.4×1.0) on their eyepiece holders. More recently I bought a Baader Maxbright mirror diagonal, which also uses these thread sizes, and some eyepiece holders with brass compression rings instead of set screws. This web page illustrates some of the useful (and not so useful) ways these accessories can be combined.
| Accessory | Thread sizes | |
| Eyepiece end | Scope end | |
| Baader 245 6100 T-2 mirror diagonal | M36.4 female | T female |
| Baader 150 8039 adapter | T male | M36.4 male |
| Borg 7315 helical focuser | T male, 1.25" eyepiece | M36.4 male |
| Borg 7423 adapter | M36.4 female, T male | T female |
| Teleskop-Service TST2-2 2" eyepiece holder | 2" eyepiece (brass compression ring) | T female |
| Intes 1.25" eyepiece holder | 1.25" eyepiece (brass compression ring) | M36.4 male |
| Sky-Watcher 80mm refractor | T male, 1.25" eyepiece | |
| Sky-Watcher 102mm Mak (without eyepiece holder) | M36.4 female | |
| Sky-Watcher 102mm Mak eyepiece holder | T male, M36.4 female, 1.25" eyepiece | M36.4 male |
| Sky-Watcher 200mm Dob (without eyepiece holder) | T male, M36.4 female | |
| Sky-Watcher 200mm Dob eyepiece holder | 1.25" eyepiece | M36.4 male |
Short tube 80 with a 2″ eyepiece
Sky-Watcher StarTravel 80 — Baader diagonal — Baader adapter — TS 2″ eyepiece holder — 1rpd 30mm 80° eyepiece
Logic and reason say this combination should suffer from vignetting, yet I can’t see any. The smallest restriction in the optical path is the scope’s eyepiece holder, which has a 31.7mm diameter. Subjectively, this combination is great for bird watching in my garden, giving an almost 3-D impression. The true field of view is 6°.
102mm Mak with a 2″ eyepiece
Sky-Watcher SkyMax 102 (with eyepiece holder) — Baader diagonal — Baader adapter — TS 2″ eyepiece holder — 1rpd 30mm 80° eyepiece
Theoretically this combination should have severe vignetting, as the Mak’s baffle tube is a mere 20.7mm diameter. Yet, once again, the entire 80° AFOV appears to be evenly illuminated. The terrestrial image is not as bright as with the 80mm refractor, but this is to be expected given their focal ratios. I think this arrangement is not useful, especially as I have other scopes that do wide field views so much better.
Short tube 80 and 102mm Mak with 1.25″ eyepieces
Sky-Watcher StarTravel 80 — Baader diagonal — Intes 1.25″ eyepiece holder — Antares W70 25mm eyepiece
Sky-Watcher SkyMax 102 (with eyepiece holder) — Baader diagonal — Intes 1.25″ eyepiece holder — Antares W70 25mm eyepiece
This is surely the best way to use 1.25″ eyepieces with these scopes. The diagonal is securely held in perfect alignment, and eyepieces are firmly gripped (without marking their barrels) whilst being easy to change.
Astrophotography with a short tube 80
Sky-Watcher StarTravel 80 — Borg 7423 adapter — Borg 7315 focuser — TS SuperView 40 eyepiece — ScopeTronix Nikon 4500 T adapter — Nikon 4500 camera (not shown)
Fine focusing is very useful in astrophotography, and as the short tube 80 without a diagonal does not have enough “out-focus” the Borg helical focuser kills two birds with one stone. I haven’t yet tried this combination out under the stars, so can’t comment on how well it actually does.
Astrophotography with a 102mm Mak
Sky-Watcher SkyMax 102 (without eyepiece holder) — Borg 7315 focuser — TS SuperView 40 eyepiece — ScopeTronix Nikon 4500 T adapter — Nikon 4500 camera (not shown)
This was my first decent astrophotography setup. Getting the camera as optically close to the scope as this is important, as Maks (and SCTs) usually have optimum performance (minimum spherical aberration) in a “telephoto lens” configuration. This combination is a joy to use. You can see some pictures taken with it on my astro photos web page.