Vixen SD103S apochromatic refractor

A portable scope that happily multitasks for both observing and imaging duties

Smaller aperture refractors, such as the Vixen SD103S apochromatic refractor we’re reviewing here, are a popular choice for both visual and imaging tasks. The unobstructed aperture of these purely lens-based instruments delivers higher-contrast views that are superior to those achieved with reflectors or SCTs of similar size. With those types of telescope, it’s the use of a secondary mirror that diffracts incoming light and ultimately reduces the view’s contrast.

Where refractors do fail, though, is in terms of price per millimetre of aperture. A large aperture reflector or SCT will typically cost significantly less than a similarly sized refractor. In addition, while a large SCT is relatively easy to handle, a large refractor will typically be long, heavy and unwieldy.

The Vixen SD103S has a 103mm objective lens with a focal length of 795mm, making it an f/7.7 mid-speed instrument. This means that as well as being a fine instrument for visual work, the SD103S should make a superb imaging telescope. The SD103S’s internal baffles have been redesigned from previous models to allow large sensors, such as those found in full-frame DSLRs, to be fully illuminated. In our tests we found that although this was the case, an amount of vignetting still occurs in the extreme frame corners, an issue easily fixed by flat-field calibration.

The focuser draw tube has a 60mm thread and is supplied pre-fitted with a 2-inch adaptor ring. The focuser is of the Crayford-style. Adjustments are basic with just a focuser stiffness tension knob. Tightened, this locks the focuser in position. We were impressed with the strength of the lock – even a heavy camera with a bit of manual assistance wouldn’t budge.

Balancing act

The SD103S weighs in at 4.7kg and is extremely portable. A carry handle makes it very easy to transport and lift onto a mount. The supplied mounting plate is of the classic Vixen type rather than a rail and requires a smaller Vixen mounting clamp for a secure connection. Once mounted, the tube rings are easily loosened and tightened to allow the telescope to slide back and forth for balancing. A flip-mirror diagonal is supplied. This slides into the 2-inch focuser adaptor ring and presents two

SKY SAYS… The high-spec optics simply ooze quality, producing images of stunning clarity and crispness