Telescope AC 90/500 OTA

Real Bargain!

( 5 / 5 )

This scope is a real “sleeper”. Hard to imagine you can obtain this level of quality for $200 (US) and $10 S&H. The closest competitor is the Orion Short-tube 80 f/5 which is a very popular beginner grab-and-go scope, finder and guide-scope. The Orion Short-tube 80 mm weights 2.25 lbs. vs. 4.85 lbs. for the Omegon 90 mm.

So what makes this scope so special? For starters it is all metal, has a 90 mm (3.5 in.) aperture (same as the Questar), a very simple but functional Crayford focuser which will accommodate both 2 inch an 1.25 inch eyepieces. The focus travel is very generous (70 mm) and has nearly 3 times more focus travel than my $3,000 Takahashi! The objective comes with a retractable lens hood. The tube is white powder coated (?). Other premium items include: adjustable tube rings, mini Vixen style dove bar, metal focuser knobs, 2 internal metal baffles (to reduce stray light), flat black tube interior, metal black anodized screw on lens cap, fully multicoated air spaced Fraunhofer achromat objective, 500 mm focal length, and f/5.6 focal ratio (very fast for a refractor). This f/ratio makes this telescope an excellent visual telescope for wide field views of the Milky Way (what we used to call a RFT or richest field telescope).

The lens arrived in pristine condition without even a speck of dust on any of the 4 surfaces. The scope even comes with a light duty zippered case with carry strap. Initial optical tests showed hard diffraction disks at 80x, perfect collimation and no on-axis astigmatism. There is some spherical aberration which is to be expected However, this level of optical performance is hard to find in a fast f/ratio telescope below $800. The achilles heel for this telescope is the chromatic aberration (or secondary color). This creates a fringe of color (in this case bright yellow) around bright objects like the Moon, Venus and bright stars (i.e. Sirius). At higher magnifications >75x it also creates a pinkish-blue color veil over extended surfaces which tends to reduce some image contrast. When viewing at higher powers some may find the color objectionable. There are anti-fringing filters that can significantly reduce this aberration, however they do so by creating a color imbalance. In viewing the Moon at powers of 25x to 100x I was impressed with how quickly I was able to obtain a crisp focus. The view Aristharcus and the nearby rille was impressive!

Other minor complaints are the dove bar is really short making it necessary to loosen the tube ring assembly to balance the tube. The tube cannot be easily removed from the tube ring without removing the focuser (it is hinged). The tube rings are not lined with felt so be sure to not tighten it too much so as to avoid marring the paint. There is no provision for mounting a finder, but to be fair this scope doesn’t need a finder, since one of its functions is to serve as a finder! If you plan to use this scope as a visual telescope I would recommend a red dot finder such as the Rigel Systems. I have not yet evaluated the scope for terrestrial viewing, nor have I taken any digital images through it.

If you don’t mind the color at the higher magnifications this may be an excellent starter scope for wide field views of the night sky, observations of the major planets, Moon, and Sun (with proper filtration, of course). I haven’t had this much fun with a new telescope in many years! I highly recommend this telescope (for newbies and experienced amateur astronomers). Worst case, if your not happy with it you can pass it on to your kids or grandkids.