* Astronomy

Helios Refractor - Startravel  (102mm (4") F/500) Refractor Telescope

The Helios 102 (now Sky-Watcher) compact rich field scope features an excellent 102mm fully multi-coated objective lens.  The short tube Startravel-102 provides 62.5% greater light gathering capability than 80mm telescopes. Like most achromatic telescopes there is some noticeable, but minor, colour aberrations around bright sources.  Filters or front lens mask can eliminate this to an unnoticeable level (for a short-focus refractor this is remarkable).
It has been said that in its price range it is one of the best refractors available.  These telescopes do occasionally appear on the second-hand market and are readily snapped up (Expect to pay between £100 - £150 [Pristine with original packaging or accessories] - even though a new Sky-Watcher telescope only costs £190).

Standard Specification:
Magnification Range x20, x40, x50, x100
Objective lens diameter 102mm
Telescope Focal Length 500mm (f/5)
Eyepieces Supplied (1.25") 10mm & 25mm Plossls (multi-coated)
2.5 degree FOV (20x) with the 25mm Plossl
1 degree FOV (50x) with the 10mm Plossl
x2 Deluxe Barlow Lens (With Camera Adaptor)
6x30 Finderscope
EQ-1 Equatorial Mount with flexible fine control shafts and field tripod
Direct SLR Camera Connection
Aluminium Tripod with accessory tray
Fully multi-coated optics
Weigh 7.5 kilos

Technical details:

-- Limiting visual magnitude: 13.1
-- Resolution: 1.13"
-- Optical system: Achromatic Fraunhofer design, multi-coated
-- Focuser: 2", with reducer to 1.25" and T2

The construction of the telescope is mostly enamelled steel or aluminium and  gives the impression of being very hardwearing.
The Lens shade is functional and gives the telescope a finished off appearance.
The front dust cover has a secondary light reducing aperture (58mm), which is ideal for looking at the moon or daylight viewing.

The 6 x 30 finder is very clear, and focused by turning the front objective housing and locking ring.  However, the straight through design sometimes places the viewing angle at an awkward position. The finder mount is well designed and sufficiently long as to be of use. The 'zeroing in' is a breeze with the two adjuster screws. And reasonably sturdy; once set up, not to be knocked out of alignment.

The focuser is excellent, and can accept 2" diagonals.  A small locking screw, located on top, will stop any unwanted movement. The focuser wheels are made from plastic, and looks slightly cheap; but on the positive side, will be warmer to touch than cold metal in winter.
The 1.25" reducer has a conical or bevelled fitting, and held securely in place by two standard lock screws. The bevelled fitting allows for the quick and simple rotation of the diagonal (rather than using the single lock screw holding the diagonal).
The inside of the 1.25" reducer is threaded. The outer edge has a standard M42  thread to allow a camera to be fitted with a suitable T-mount.

Short-focus refractors like the Helios/sky-watcher 102mm would be not the ideal choice for as a planetary scope. The main strengths of the scope lie on good low-power views of deep-sky objects, and 'portability'.
Having said that, it will deliver very high contrasty planetary images with chromatic aberration correction filters and a quality Barlow lens.

The EQI mount and tripod are the bottom of the scale for mounts, but this version is of decidedly better quality than newer versions. Without a polar alignment scope, there is, of course, no quick way to set up the scope (unless you have a preset viewing position).  For visual work the mount is more than adequate. A bonus is that RA motor drives are very cheap for this version.