Excellent eyepiece. You cannot go wrong with these

I'm from Mexico, i hope that my review on spanish help someone. Lo cierto es que aun investigando y viendo videos sobre los lentes es dificil decidirse por uno, sin saber como se ve. Yo ya tenia el hyperion 8mm, sin expansiones ni nada, se puede ver la luna y los planetas bien, combinandolos con un barlow tambien se puede ver un poco mas cerca. Me decidi por el hyperion 21mm porque las combinaciones con las expansiones te dan un mejor acercamiento a lo que quieras observar. Cuando por fin pude probar las diferencias de los 2 (21mm y 8mm) basicamente depende de que quieras ver. A mi me gusta sacar fotos de la luna con mi celular y eso lo hago con el 8mm y las 2 expansiones (tuning ring 28mm y 14mm). con eso se puede ver sin barlow la luna muy bien. El 21mm tiene mas amplitud en el campo focal y puedes ver mejor las nebulosas, ademas con algún filtro se pueden ver mucho mejor. La verdad es divertido usarlos, porque puedes jugar con filtros, las expansiones y los distintos tamaños de lentes. Depende mucho de que quieran observar, pero creo que es una buena compra tenerlos.

Excellent addition to my eyepieces; I have 2 Orion Stratus eyepieces 5mm and 13mm and a 30mm; this one fills the magnitude gap nicely and is of great quality

Parfocal with Baader 36mm. Nice wide field.

Excellent- finely constructed. Beautiful crisp views in mt 8 Celestron SC. The price is a winner! OPT is a great dealership! Mike Anderer Saint Charles, Il

I currently own the 5, 8, 13 and 21 mm models (and saving for the 36 mm. I use them in my 3 small (typical urban observer telescopes: Meade ETX 90 mm f/14, and Bushnell 127 mm f/12 Maksutovs, and 80 mm f/5 short-tube doublet refractor (***** A80-SSWT. The Hyperions look and feel big on these small scopes, but that's just about it, you can very easily get to using them without problems of handling or balancing. Optically, they do great, very honestly delivering the wide field and ample eye relief stated in the specs, and all with very good illumination and contrast. The only optical drawback is some evident, but reasonably expected and tolerable, edge distorsion when using the 13 and 21 mm in the f/5 short-tube. This is manifested by coma and spherical distortion in the outer surroundings of the viewfield, noticeable starting from around 2/3 out of the center while in the larger central region, the image is still quite excellent. I have done Moon, planets, star fields, and brighter fuzzies with the Hyperions all of it very satisfying observing. I can only imagine how they deliver in larger scopes or darker skies, but my humble experience with my urban lot of small scopes tells me these eyepieces should do very fine indeed. If buying a small basic set of Hyperions, I may suggest geting the 13, 8, and 21 or 24 mm (in that order as perhaps the most generally useful with any scope. As for myself, I tend to use 21 and 8 mm with the Maks, 13 and 5 mm in the f/5. The 5 mm gets too dim and washed out (over-magnified in the Maks while the 21 mm gives too much urban sky glow, besides edge distortion, in the short-tube.