Omegon AP 104/650 ED refractor.

A well-built 4-inch scope that delivers good contrast

There is no doubt that the Omegon AP 104/650 ED apochromatic refractor stands out from the crowd. The glossy black tube is stylishly complemented by the red metallic fittings, and the solid build inspires confidence in the quality of the telescope. The fit and feel is certainly that of a professional instrument.

The Omegon AP 104/650 is packaged with a separate 2-inch field flattener, an accessory that prevents the effects of coma at the edges of photographs. The spacing between a flattener and a camera depends on the focal ratio of the telescope. The Omegon 140/650 ED is f/6.25, so we set our full frame DSLR camera to the specified 113mm spacing using our own adaptors.

Our first optical test was to check focus and colour correction across the imaging circle. We found that with the flattener in place the telescope provided sharp round stars to the majority of the field. At the very edges of the full frame picture a little distortion was visible. Cameras with smaller sensors (like CCDs) should be unaffected and produce pictures of crisp stars with tight colour correction.

With limited clear skies we used a more sensitive colour CCD camera with a smaller sensor to acquire the night-sky images you see over the page. The scope’s multicoated optics, internal baffling and extending dew shield all assisted in creating good contrast in our images and views, and despite the skies being decidedly murky during our photography sessions we were still able to use the scope to produce some reasonable photos in a short time.

The working focal length of 650mm is useful for a wide range of deep-sky objects – powerful enough for larger galaxies and wide enough for extended nebulae. We were pleased to see that even small, faint objects and stars were well resolved, such as the little cluster NGC 206 in the outer arms of the Andromeda Galaxy.

The proof is in the fitting

Astrophotography with the Omegon is straightforward. The geared, 2.9-inch Crayford focuser allows you to attach a camera via a standard 2-inch nosepiece. Removing the end of the focuser reveals an M74 thread, which offers a more solid fitting for larger cameras.