Vixen overhauls its classic large refractor in the SD103SII. We tested its observing and astro-imaging potential

Vixen’s original and popular air-spaced doublet, the SD103S, is a large refractor and stalwart Vixen product that will be familiar to most astronomers.

To keep it up to date among an ever-growing, competitive refractor market, Vixen has overhauled the optical design to produce the new Vixen SD103SII.

We were excited to see how it had improved.

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Unboxing

We unpacked the SD103SII and were pleased to find the telescope finished in Vixen’s traditional ultra-glossy white paint, presenting a high-quality and solidly built finish.

A pair of matching tube rings, a small Vixen dovetail bar and a carry handle came already fitted to the telescope, while the flip mirror diagonal and matching 7x50mm finderscope were secured separately in the box. 

One thing we noted is that the Vixen dovetail bar is specifically engineered for use with Vixen-designed mounts.

The bar is only shaped on the centre third, while the thumbscrews to tighten the tube rings are next to the foot, which impede the bar from being inserted into some other mounts.

To get around this, the carry handle on the top of the tube rings can be removed and a larger Vixen or Losmandy bar fitted in its place. 

How the Vixen SD103SII performed

With a clear night ahead, we headed outside to give the Vixen SD103SII a good 45 minutes to cool down, given its solid construction and large glass elements.

We then fitted the included (and handy) flip mirror diagonal.

This allows the connection of both an eyepiece and a small camera to the telescope, and flips between the two.

With a 25mm Vixen eyepiece fitted, we slewed over to the Double Cluster in Perseus.  

During the focusing process, we noted some mild astigmatism just outside of focus.

Moving further out of focus gave us perfectly round discs across the centre of the field.

However, the stars towards the edge appeared as semi circles, suggesting something was clipping the light path.

Swapping out the flip diagonal for our own 1.25-inch diagonal and a different 25mm eyepiece, the star shape was unchanged.

However, stepping up to a 15mm eyepiece improved things and we found that the stars were round to the edges.

Moving back to focus, we found that the Vixen provided us with great views of both clusters.

Slewing over to the Orion Nebula, we were able to see some lovely structure in the nebula with the 25mm eyepiece, while a 15mm eyepiece allowed us to easily resolve the central Trapezium stars.

Astrophotography with the Vixen SD103SII

With the SD103SII marketed as being compatible with full-frame cameras, we attached our full-frame Canon 6D DSLR.

Again, we found precise focus easy to achieve, with small adjustments proving straightforward even with the single-speed focuser.

With everything set, we began our imaging session on Orion. 

The following day, we started post-processing.

We quickly saw that there was no traditional vignetting visible and the stars appeared round into the corners.

However, there was a notable halo through the image, which was not corrected by reprocessing with our calibration frames.

A couple of weeks later, clear skies returned and, keen to image again, this time we attached the optional HD field flattener/reducer combination that Vixen offers.

Despite the bright, waxing Moon being in proximity, the flattener completely removed the halo previously seen. 

With the Moon making its presence felt, we removed our DSLR and the flattener, and switched to our CCD, this time selecting a target further away for a night of narrowband imaging.

Processing the images produced from our crop-sensor CCD camera, we were again happy to see that the halo was not present and the stars were tight and round. 

Overall, the Vixen SD103SII was a pleasing telescope to use and gave some excellent views in visual use.

When paired with a camera, it has the potential to produce a range of great astro images.

However, the optional Vixen flattener/reducer allows this refractor to really shine if coupled with a full-frame device.

Upgrades

The updated Vixen SD103SII uses the same fundamental 103mm optics as the original SD103S, maintaining the punchy 795mm focal length (f/7.7) that maximises its suitability for lunar and deep-sky targets.

While its appearance is unchanged, there are important changes within the optical assembly. 

The original model was an air-spaced doublet that utilised spacer discs.

Each disc had three tabs that protruded slightly between the lenses and created the effect of diffraction spikes when viewing or imaging brighter stars.

This revamped model has an improved lens cell that no longer uses these spacers, removing the protrusions into the light path.

As a result, the spikes previously seen were not apparent during our visual sessions and none could be seen in any of our images. 

The FPL53 ED glass in the SD103SII, sometimes referred to as synthetic fluorite, is well known for its ability to control colour fringing.

This proved to be the case during testing, where a well-cooled telescope aligned on the bright Moon with no noticeable colour fringing apparent.

Vixen SD103SII best features

Flip mirror diagonal

The SD103SII comes with Vixen’s flip mirror diagonal. A 2-inch barrel connects to the telescope and allows access to a pair of 1.25-inch adaptors. With a simple twist of the diagonal, we could easily switch from a 90°-angle standard diagonal to a straight-through barrel that securely holds a camera.

Vixen foot, tube rings and handle

Attached to the underside of the white tube rings is a short Vixen dovetail bar, while on top is a sturdy carry handle. As the dovetail bar is short, you can easily loosen the tube rings to allow the telescope to slide within them, achieving perfect balance.

Dew shield

A large, removable, solid-metal dew shield and a lens cap come fitted to the Vixen as standard. This long dew shield prevented the main lens dewing up over the course of multiple hours, despite the damp evenings. The shield also helps to stop stray light from entering the telescope.

Single-speed geared focuser

The Vixen SD103SII comes fitted with a 60mm single-speed focuser. This very smooth and solid-feeling focuser will easily carry heavy camera equipment thanks to its tension adjuster. We found that precise focus could be easily obtained with all our eyepieces, although additional spacers were required when imaging.

Illuminated finderscope

Included as standard is a 7x50mm view finder that attaches to the SD103SII via the provided mounting bracket. The finder comes with an illuminated eyepiece that makes finding objects a breeze. You can also remove the illuminated eyepiece and use the finder as a guidescope.

Vital stats

• Price: £2,056
• Optics: FPL53 glass, doublet refractor
• Aperture: 103mm
• Focal length:  795mm, f/7.7
• Focuser: Single-speed geared
• Extras: Tube rings, dovetail bar, carry handle, illuminated finderscope
• Weight: 5.5kg 
• Supplier: Telescope House
• Tel: 01342 837098
• www.telescopehouse.com

This review appeared in the June 2024 issue of BBC Sky at Night Magazine