The latest model in StarField Optics’ growing line of “Géar” refractors, at least as of this writing, is the Géar115, a triplet apochromat.

Its aperture of 4.53 inches edges it into the class of moderately large refractors, while its slower-than-usual f/7 focal ratio yields a focal length of 805mm. Compared to more common 80mm to 90mm f/5 or f/6 apo refractors, the Géar115’s larger aperture and longer focal length makes it more suitable for planetary viewing and imaging smaller deep-sky targets.

Visual Performance

As with the other Géar apochromatic scopes, the 115 employs one lens element in its triplet design made of premium Ohara FPL53, a top grade of glass prized by refractor lovers. Examining stars and planets at high power showed the FPL53’s advantage over less expensive glass such as FPL51. Views of Jupiter and bright stars were entirely free of any false colour haloes or fringes.

It was only when racking out of focus that a mild cyan rim showed up, outside of focus, around the defocused disks of Jupiter and bright stars. At the same time, a pale magenta rim was visible inside of focus. This was a slightly more chromatic aberration than I had observed in the smaller Géar80 I tested in the March/April 2022 issue of SkyNews. But the larger aperture and greater light gathering power of the Géar115 means it will reveal subtle aberrations all the more. 

When in focus at high power, the stars looked textbook perfect, with a well-defined central Airy disk surrounded by a faint first diffraction ring. Racking just inside and outside of focus showed the mildest level of spherical aberration, in that the two “extra-focal” disks were not quite identical. That is true of most telescopes, as this kind of star test is sensitive to the slightest aberrations. 

As with the other Géar refractors, the 115 comes with a test report unique to each unit, showing the lens’ performance in a bench test. My test scope had a Strehl ratio of 0.978 (with 1.0 being impossible perfection), and a peak-to-valley wavefront error of a very low 0.20 wave (1/5-wave). This accords with my visual tests. 

My loan period coincided with the close approach of Mars, and on the few clear nights I had, the Géar115 provided some wonderfully sharp views of the red planet, using a 4mm eyepiece for 200×.

Photographic Performance

I also tested the Géar115 for deep-sky imaging using a camera with a full-frame (36mm × 24mm) sensor — the Canon EOS R5. 

The sensor’s 45 megapixels places high demands on any optics. Without any field flattener lens, star images appeared pinpoint-only in a central image circle of 20mm — not unusual for refractors. This might be fine when using a camera with a micro-four-thirds sensor, one measuring 17mm × 13mm. Cameras with larger sensors will require adding a field flattener lens to sharpen stars out to the corners.

StarField offers two: the 1.0× Adjustable Flattener, which retains the f/7 focal ratio and 805mm focal length; and the 0.8× Adjustable Reducer, which speeds up the focal ratio to f/5.6, yielding an effective focal length of 644mm. This can cut exposure times by almost half, and widens the full-frame field to 3.2 degrees by 2.1 degrees — compared to the native f/7 field of 2.5 degrees by 1.7 degrees. 

Both flatteners offer a unique helical adjustment for shifting the camera in and out to place its sensor at the optimal distance from the optics for the best correction. This does away with fiddling with special spacer tubes some cameras might require.

Once set to their recommended spacings, both flatteners provided superb correction, with stars appearing as pinpoints right out to the corners. In terms of performance it was an improvement over what I had experienced with the Géar80, along with most other refractor/flattener combinations that often leave stars looking a little elongated at the extreme corners. Not so with the Géar115. I also saw no evidence of any tilt in the camera mounting; stars were uniformly sharp across the frame. 

The choice of two excellent flatteners makes this a versatile telescope for imaging. Use the 0.8× unit for larger deep-sky targets, or the 1.0× unit for resolving smaller targets like galaxies and globular clusters. However, while the 1.0× Flattener will work on all the Géar refractors, the 115 requires a special 0.8× Reducer, the larger “L” model — not the “S” model needed for the smaller Géars.

Mechanical Features

The focuser is all-important on any telescope designed for imaging. The large 2.5-inch focuser common to all Géar scopes is among the best I have seen. Movement is smooth and free of backlash, with the 10:1 fine focus knob allowing precise adjustments. 

The entire focuser can rotate to place the focus knobs at the most convenient orientation. In addition, a separate “camera angle adjuster” allows turning a star diagonal or camera to the desired angle. The rotation mechanisms proved smooth, and did not introduce any focus or image shift.

The only glitch I encountered was on cold nights when the focuser’s fine focus motion could slip when traveling inward against the weight it was carrying. Slightly backing off the tension screws on the underside of the focuser helped solve this issue. I liked the large lock knobs employed throughout; they are great on winter nights with gloves on. While the dewcap does not have a lock knob, it didn’t need one; even on cold nights when aimed up it stayed in place.

The Géar115’s 6.5 kilogram mass (without accessories) will require the use of a solid middleweight mount, especially for imaging. With the required flattener lenses, the combination will be a serious investment. 

However, for a refractor fan looking for a scope with more aperture and focal length than an 80mm or 90mm model, but without the cost and weight of a 130mm, the Géar115 is a choice I can highly recommend. Its optics come close to matching the best I have tested, and its mechanics make it a constant pleasure to use.