Starwave 152mm f/5.9 achromatic refractor — Part 2
Altair Astro —
Written: October 2013

Planetary Prowess
During a pre-dawn viewing session on Monday, October 21st, I had the opportunity to observe the 16-day-old waning gibbous Moon and planet Jupiter in a clear sky under fair to good (occasionally very good) seeing conditions. By the time the Starwave 152mm achromat had reached ambient temperature the Moon was about 35° above the west-southwest, but Jupiter was ideally placed near my meridian and close to 60° in altitude.

I used a William Optics 24mm DCL-28 eyepiece in addition to the 7mm and 4mm TMB Planetary oculars from Part 1. All three are 1¼-inch format. Since I was not enamoured of the Baader Fringe Killer filter because it delivered (in my opinion) a colour cast that was too warm with this telescope, I kept the views unfiltered.

Just two days and a few hours past full at the time of observation, the 95% illuminated gibbous lunar disc was a stiff test for the 6" f/5.9 achromat, but the 'scope acquitted itself extremely well. The view was exceedingly crisp and dazzling in the William Optics 24mm eyepiece at 38x (though 6-element eyepieces would be a better choice for this f/5.9 instrument) with a thin purple fringe of chromatic aberration to the lunar limb and a diffuse violet wash to the scene. This effect was more noticeable with the 7mm at 129x and obvious at 225x with the 4mm. However, crater detail still snapped into focus and I felt that the instrument delivered the full resolution of its unobstructed 6-inch objective. Sweeping south along the terminator from the eastern ramparts of the Mare Crisium past spectacular impact craters Langrenus and Petavius (the latter neatly revealing its extensive rille system) and on through the southern highlands presented scenes of sharp, seemingly inexhaustible detail.

At the start of observations the Sun was 15° below the horizon, so Jupiter was seen against an essentially black sky (moonlight notwithstanding). The planet exhibited a crisp limb with a narrow purple fringe surrounded by a deep violet halo, but the disc was full of detail. The main equatorial cloud belts displayed structure, the N. Temperate and N. N. Temperate Belts were nicely delineated, as was the S. Temperate Belt. However, the main reason for observing 5:00—5:40 UT on October 21st was to observe largest Galilean moon Ganymede slip behind the Jovian limb into occultation. Io, Callisto and Ganymede (Europa was still occulted by its parent planet at this time) were revealed as tiny discs rather than having a stellar appearance, further testimony to the Starwave 6-inch doublet's good figuring. Ganymede looked like a tiny bead as it approached Jupiter's limb and I managed to see it disappear close to 5:35 UT.

The designers of this telescope have clearly optimised the colour balance for visual yellow/green wavelengths with an unobjectionable secondary spectrum overspill for such a fast focal ratio, primarily in the deep violet. I believe that the Starwave 152mm f/5.9 betters the resolution, contrast and colour correction of typical 6-inch f/8 doublets currently on the market for lunar and planetary observation, plus its deep-sky performance is outstandingly good. If you're looking for an extremely well crafted and compact 6-inch refractor primarily for stunning wide-angle deep-sky views, one that will not overtax an EQ5-class equatorial and turn in a decent planetary performance when the need arises, the versatile Starwave 152mm f/5.9 may be the only 'scope that you will ever need.

As an experiment, my friend Ian Nicol used his unmodified Canon 550D with a light pollution filter at the Starwave 152mm's f/5.9 prime focus to capture this image of the Dumbbell Nebula on October 23rd at 18:28UT. Settings: ISO800, 60 second exposure (with internal dark frame subtraction), Celestron CG5-GT mount (unguided).

Narrow-band imaging is entirely possible with this telescope. For example, a Canon 1100D DSLR will capture 1.7° of sky (diagonal) at the 900mm focal length.

v1.2 — 25th October 2013