RVO Horizon 72ED refractor
An impressively lightweight telescope that fits the bill for visual observing and imaging
Short focus refractors have definitely made their mark, becoming very popular in recent years, and the new RVO Horizon 72ED is set to join them. The improved performance of such refractors makes them easy to use, quick and simple to mount and ideal for transporting to find better skies, whether it’s for foreign travel or to a nearby dark-sky site. Although far-off travel has been difficult in recent times, this had little impact on our tests because we had the refractor during one of the longest periods of clear skies we can remember.
The Horizon 72ED, produced by Rotherham-based Rother Valley Optics, has a 72mm objective doublet lens with a focal length of 432mm, giving a focal ratio of f/6. The doublet is composed of FPL-53 glass, an extra-low dispersion glass that gives the telescope the ‘ED’ in its name. This helps to correct the slight spread in the wavelengths of light which produces chromatic aberration, or colour fringing, a defect often found in such short focus refractors when they aren’t properly corrected. The scope and tube rings come in the RVO colours, a stylish white tube with a sky-blue visual back and orange detailing. The orange tube rings are attached to the extra-long Vixen-style mounting bar with small risers, which prevent the focus lock screw catching on the bar.
Deep-sky viewing
The basic package consists of the telescope with a visual back that accepts 2- and 1.25-inch eyepieces and accessories, the latter size accommodated by a 2- to 1.25-inch adaptor in black. Also included is a finderscope shoe and a smaller top Vixen bar, which allows you to mount additional accessories. Adding a mount of your choice, along with a star diagonal and eyepieces will create a wide-field setup, ideal for taking a visual tour of the Milky Way star fields, or viewing large clusters such as the Coma Star Cluster (Collinder 256) or the Pleiades and the Double Cluster in Perseus. The 72ED is also sold in a £947 imaging package aimed at deep-sky astrophotographers, which includes a 1.0x rotatable field flattener and a finder/guidescope.
Although the Pleiades wasn’t visible when we had the Horizon 72ED, we enjoyed the rest of our selected targets visually. In our tests with a 26mm 2-inch eyepiece, at a magnification of 16x, we found the view to be pin sharp out to 80 per cent of the frame. It trailed off slightly towards the edges, but this is expected with such a fast focal ratio. The colour correction was spot on and, even when we pushed the magnification, we found our views of Albireo – with its gold and sky-blue components – were superb.
Encouraged, we swapped to a trusty 1.25-inch 26mm eyepiece and added our 5x Powermate to push the magnification to 83x, before aiming at the triple star Iota Cassiopeiae, which was low in the northern sky. We could easily see the further, fainter companion but the closer, brighter component only flickered into view. Increasing the power again we swapped in our 9mm eyepiece to give a magnification of 240x and brought all three components into view.
Grand tour
Dropping back to the 26mm eyepiece, and occasionally the 9mm ocular, we took a deep-sky tour. We can report pleasing views of our targets – including galaxies M81 and M82, the Double Cluster, M52, M11, M39, M17, the Coma Star Cluster, and the Dumbbell and Ring Nebulae.
Now it was time to attach a camera and begin imaging. We wanted to see how the basic telescope performed first, so we used our modified Canon 300 DSLR on the North America Nebula. Framing it so that the Pelican Nebula was also included, we took 78, 60 second exposures at ISO 1600 and stacked them with 10 dark frames using Astro Pixel Processor. We were thrilled with the result, but there was some coma towards the edges, which is to be expected with the fast focal ratio of f/6. RVO’s 1.0x rotatable field flattener, which is extra (see Kit to Add), will correct this optical abberation. For our next test we tried the scope and camera with the loaned field flattener, taking 119, 60 second exposures of the nebulosity surrounding Sadr in Cygnus, at ISO 1600. The result was again pleasing, with pin sharp stars at the edges. It backed up our overall impression, that the Horizon 72ED is a cracking instrument for both wide-field observing and imaging.