GTO Plossl Review

By Milton Esquinaldo

Fit and finish

25mm Plossl

The fit and finish of the 25mm plossl seem good to very good. The eyepiece has an unusual smell to it. It smells like rubber (I guess from the rubber surround). Overall I would rank in about par with other generic plossl eyepieces that are available on the market. I would have to rank this at about 80% of the fit and finish of Plossl’s costing much more. The eyepiece looks to be coated with at least 1 layer of MgFl coatings giving a light blue tint to the glass. It looks to be effective in reducing glare.

Shorty Barlow

The barlow looks almost identical to the Orion Shorty Barlow available for about $45 from the Telescope and Binocular Center. The unit I received had a loose barrel from the top housing. A bit of superglue fixed the barlow to working condition. I would have to say that the finish is again about 80% of Shorty barlow purchased from Orion. The lenses look like at least 1 layer of MgFl coatings are on them - they show a light blue tint.

Performance

25mm Plossl

I will judge the performance of the 25mm plossl as compaired to an Orion Explorer II eyepiece available at around $35 from the Telescope and Binocular Center. I will look at 3 areas in testing this eyepiece in comparison to the Orion eyepiece – (1) edge shapness, (2) contrast, (3) clarity of image. I will also look at the overall field of view.

The field of view as compaired to the Orion eyepiece is slightly smaller – approximately 48 degrees. This in no way hindered its performance. The eyepiece shows only a small amount of color on very bright objects such as the full moon. Views through the eyepiece were contrasty and sharp – somewhat sharper than the Orion Explorer. From time to time I could detect a very slight yellow tint to the color of the moon. The tint was so slight that in no way hindered the performance of the eyepiece.

Edge sharpness in the eyepiece were about the same for both the GTO and Orion Explorer. In a fast f/6 refractor, sharpness fell off sharply at about 25% from the edge. Both eyepieces fell of in sharpness from about 10% of the edge with an f/12 scope. When barlowed, both eyepieces were very sharp to the edge; however, the Orion vignettes very badly when barlowed. I was somewhat surprised to see this happen. The GTO showed no sign of vignetting at all.

Overall, I would rank the GTO as a better overall performer than the Explorer at a better price. Especially given the price, it is worth strong consideration as a "workhorse" eyepiece.

Shorty Barlow

I did a comparison (perhaps unfairly) to the Celestron Ultima barlow. Surprisingly, the GTO Shorty did an admirable job as compared with one of the finest barlows available. Image sharpness and color correction were noticeably better in the Ultima, but still very, very good for the GTO. At higher powers, more color was detected, but not to the point that it was annoying.

One afternoon, after comparing the two barlows, I decided to look through the GTO alone (without comparison to the Ultima). Without direct comparison, the barlow performed exceedingly well, which tells me that in real world performance, it would do an excellent job. The barlow did not display any annoying characteristics or aberrations – which is what a barlow is supposed to do. As I see it, a barlow is to double the magnification of an eyepiece – otherwise it is to be "transparent." The GTO did an excellent job of "getting out of the way" and allowed me to do all my viewing without hindrance or complaint. It was only with direct comparison to the Ultima barlow that I could detect any differences. Without the Ultima handy, I did not notice any difference.

All in all I would have to rate the GTO barlow as a best buy. Its performance is about 80% of the Ultima Barlow and a fraction of the price. I am glad that I have one for a workhorse barlow.

Milton