This Astro-Tech 19mm PF series eyepiece has excellent eyerelief and a fantastic flat field to further enhance your viewing pleasure. So, I know someone will wonder what exactly PF stands for. It isn't just some letter choosen at random for reasons unknown. They actually stand for Premium Flat Field.
This Astro-Tech 19mm PF eyepiece is an excellent medium to medium low power eyepiece for all types of observing in all types of seeing conditions. As long as you aren't out observing in a blizzard or downpour, you should be good. A focal length like the 19 fits a natural step left behind by most telescopes standard 25mm or so eyepiece. Their physical size and flat field would also make them excellent choices for a binoviewer.
With a short focal length refractor it is a low power eyepiece. With the 430mm focal length Astro-Tech AT72EDII, for example, its five lens/three group multicoated glass optics provide 22x and a field over five times as wide as the full Moon. This is well suited for lunar observing, encompassing globular clusters, getting lost in the faint details of emission and reflection nebulas among other things. This series of eyepiece is designed to have an inherently flat field, so it will excell at wide field observation.
It functions so well for medium high magnification observing with long focal length refractors, reflectors, or catadioptric scopes. On an 8" f/10 catadioptric, for example, it yields 105x. You can get lost inside clusters or just gazing at the moon for hours on end.
The five lens/three group design of the 19mm Astro-Tech PF provides all of the optical virtues described at the top of this catalog page - high contrast, a sharp and flat field from edge to edge, excellent color fidelity, and exceptionally low astigmatism and barrel distortion. It has a usable eye relief of 20mm, which is just excellent for all observers. The eyepiece some with a traditional rubber fold down eye cup to assist that glasses wearers of the world find a comfortable eye position. This particular eyepiece has a nice 65° apparent field of view, which is a tad wider than the 5.5 and 10.5 PF.
Enjoy the night skies with this very reasonably priced premium eyepiece.
