The Celestron 80mm ED

Posted by Doug Peterson   12/01/2004 08:00AM

Bottom line: the optics are of the color correction and quality of the Orion 80ED I reviewed on the sci.astro.amateur newsgroup the first day they became available, which is to say of a very high order, perhaps astonishingly high order when you factor in the bargain basement price.

The star test on mine is very good indeed, spherical correction 1/8 wave or better and very round fresnel rings.
I don’t see color wedge that is sometimes a problem with Chinese refractors even when everything else is fine.

I also don’t see coma, or astigmatism, meaning collimation is on target. No optical pinching effects are visible at temperatures close to freezing. (Tests were performed with the Nagler 2.5mm and Nagler 3-6mm zoom at up to 240x.)

Only a little violet around the fresnel rings is visible out of focus using the classic star test; in focus no color halo, only a little tight violet that pumps in and out as the focus changes randomly from the seeing. Did I say there was no color halo? All told, I can believe the optics are identical to the Orion ED.

The glass itself is cosmetically very clean. Multicoated all four surfaces--not quite as transparent as Takahashis, say, but all the colored reflections coming back from the objective are a uniform green tint.

The weight and heft seem to be less than the Orion, which I no longer have for direct comparison. If anything, the 3.5” OD tube and the 21.5” length to the 2” focuser visual-back make it feel less bulky. The dust plug fits inside the aluminum thread-on dewcap, a nice touch that won’t damage the outside finish over time.

The clamp however is problematic—instead of the traditional one or two tightening knobs, its snap-hinge design means you cannot finely control the tightness of the clamping action, and it is hard to open and close even at its least-tight position. Even though the tube was wrapped in paper with the clamp installed outside the wrapping, the tube finish as received is lightly marred. The black stippling from the imprinted paper and felt pattern catch the light, although it is a surface texture effect, not through the paint. Nevertheless it is covered up in use by the clamp itself. Overall the clamp is superior to the oddly-balanced and underpowered ¼-20 tripod block on the Orion.

Aside from the finish issue and the clamping action, the clamp itself has a molded-in dovetail directly compatible with GP-type mounts. All of the accessories shown on the Celestron website were received along with the OTA at the remarkable $409 price from Anacortes.

The focuser is definitely stiff compared to the Orion crayford, although it has the usual adjustments. It appears parts-similar to the regular Synta rack and pinion with a different cast housing that has a flared-opening dovetail-slot for the finderbase, another good idea, allowing easy assembly in the dark. The rubber-trimmed aluminum knobs are a nice touch instead of the cheesy plastic typical nowadays.

The internal baffling and blackening is up to the task, without being of the true black hole variety. The included accessories that is, the 6x30 finder, 25mm Plossl, and 45 degree erecting prism, are standard issue, which is to say much better than the vintage days of department store refractors where the oculars were merely vestigial appendages.

Others have complained about the thread-on black aluminum dew shield, but I think it is an improvement, kind of like the good old days of Tele Vue’s black powdercoated thread-on dewshields. Obviously a retractable device would be ideal, but I guess you can’t have everything for four hundred bucks.

Even with the minor issues this looks like the most budget-APO bang for the buck yet. Almost as remarkable—and an indicator of how far things have come in the last couple years—is that the words budget and apochromat can be used in the same sentence.