The Astro-Tech 19mm Premium Flat Field keeps the field wide at 65°, and delivers 20mm of eye relief that works even if you wear glasses. It's not a premium eyepiece. But with five optical elements correcting the field where the stock Plössl's four can't, it's a meaningful step up — at a price that won't make you hesitate.
The Optics
Five elements in three groups, fully multicoated. This is one more element than the 25mm PF, and the difference shows at the edge of the field. Where the 25mm's simpler 4-element design starts to soften halfway to the edge in fast scopes, the 19mm holds its correction further out. Alan Dyer's review for Cloudy Nights tested all five PF eyepieces on scopes from f/5 to f/10 and found sharp stars across most of the field, with softening only in the outer 10–15% — and that primarily in the longer focal length models at fast focal ratios. On-axis, the view is clean and free of false color, with no ghost images on bright targets like Jupiter.
The stated 65° apparent field of view measures slightly under spec according to Dyer, but closer to the mark than the 25mm. In practice, it's meaningfully wider than a Plössl's 50–52° — enough to feel the difference the moment you look through it. The field edge is sharply defined, not fuzzy, which contributes to the sense of a bigger window on the sky.
Built for the Job
At 5.2 ounces with caps, the 19mm PF is light enough to forget about on a balanced telescope. Rubber fold-down eyecup for positioning — pull it off entirely or fold it down for glasses. The 20mm eye relief is comfortable for nearly everyone, including eyeglass wearers who often struggle with shorter focal length eyepieces. Standard 1.25" filter threads accept any nebula or light pollution filter. Tapered barrel for smooth insertion. Nearly parfocal across the entire PF line, so if you build a set, you'll barely touch the focuser when swapping.
Binoviewing
The PF line was practically designed for binoviewers. Lightweight bodies, flat fields, comfortable eye relief, and a price that makes buying two reasonable. At 19mm, you get a medium-power binoview that resolves more detail than the 25mm pair while still framing large objects comfortably. Several owners specifically bought PFs for binoviewing and report excellent results.
What's Included
- Astro-Tech 19mm PF (Premium Flat Field) 1.25" eyepiece
- Lens caps (top and bottom)
- Lens cleaning cloth
Features
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65° apparent field of view — Wider than a Plössl (50–52°), narrower than an 82° UWA. A genuine upgrade in field width without the cost of a premium wide-angle design.
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5-element multicoated optics — One element more than the 25mm PF. Better edge correction, especially at faster focal ratios. Sharp and free of false color on bright objects.
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19mm focal length — Medium-power workhorse. In a 1000mm telescope, 53x. In a 1200mm Dob, 63x. In a 2032mm SCT, 107x. The step-up eyepiece from your stock low-power.
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20mm eye relief — Genuinely glasses-friendly. No peering down a tunnel. Fold-down rubber eyecup helps non-glasses users find the right eye position too.
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Nearly parfocal across the PF line — Build a set and barely touch the focuser between swaps.
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Lightweight — 5.2 oz with caps — No balance concerns. Excellent for binoviewing in pairs.
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Standard 1.25" filter threads — Accepts any standard 1.25" astronomy filter.
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Flat field design — Stars stay sharp further toward the field edge than in a standard Plössl. Best results at f/7 and slower; still good at f/5 with some edge softening.
Under the Night Sky
In an 8-inch f/10 SCT at 107x, the Orion Nebula shows real structure — the four stars of the Trapezium cleanly split, the bright inner nebulosity sculpted with dark lanes, and the fainter wings reaching toward the field edge. This is the magnification where emission nebulae start to reveal detail that low-power views only hint at. M42 is no longer a smudge with stars in it — it's a landscape.
In an 8-inch f/6 Dobsonian at 63x, the Hercules Cluster (M13) begins to resolve into individual stars at the edges instead of looking like a fuzzy tennis ball. The Double Cluster fits the field with room to spare. Saturn shows the Cassini Division on a steady night, with the planet's shadow falling on the rings. This is the magnification range where visual astronomy gets interesting — high enough to resolve detail, low enough to keep the context.
In a 90mm f/10 refractor at 45x, the Beehive Cluster (M44) is framed perfectly — dozens of stars scattered across the field. The Pleiades show the brightest members with hints of nebulosity on a dark night. And the Moon at this magnification is a full-disk view with enough power to trace the terminator's shadow across individual crater rims.
Community Says
"For no more than what this design is and for no more than what each eyepiece costs, when used with my f/7.5 and f/10 refractors, these eyepieces are a bargain. Solid feeling, comfortable eye relief, decent to good off axis correction for astigmatism." This owner tested the 19mm alongside other budget eyepieces in slow refractors and concluded the Premium Flat Field design delivers where it matters most: the view through the eyepiece, not the spec sheet. — Cloudy Nights Premium Flat Field discussion. This owner uses the 19mm in f/7.5 and f/10 refractors and prefers it over Plössls.
Observing Tip
The 19mm PF is the natural next step after the stock 25mm eyepiece, but it really shines when paired with the 10.5mm PF. Together, those two focal lengths give you a low-medium and a medium-high magnification that cover most visual targets — and because the PF line is nearly parfocal, swapping between them is almost seamless. You get a two-eyepiece kit that replaces the single stock Plössl with actual range.
FAQ
How is this different from the 25mm PF?
The 19mm uses five optical elements instead of four. That extra element buys better edge correction, especially at faster focal ratios. It also has 20mm eye relief versus the 25mm's 15mm effective — a real difference for glasses wearers. The trade-off is a slightly narrower true field of view at the same focal length telescope (because 19mm gives higher magnification), but you gain resolution on everything you point at.
Will this work in my f/5 telescope?
Yes, with a caveat. The center of the field will be sharp and clean. Toward the edges, you may notice some softening from astigmatism — that's the fast focal ratio exposing the limits of a budget design. It's still a big improvement over a stock Kellner or Huygenian eyepiece. At f/7 and slower, the field is flat and sharp nearly all the way to the edge.
Is the eye relief enough for glasses?
At 20mm, yes. Multiple owners report comfortable viewing with glasses on. The fold-down rubber eyecup helps you find the right eye position. This is notably better than the 25mm PF's 15mm effective eye relief for glasses wearers.
Can I use this for binoviewing?
The PF line is excellent for binoviewing. The 19mm gives a medium-power binoview, the bodies are lightweight enough to avoid balance issues, and the flat field means both eyes see sharp stars. Several owners bought PFs specifically for binoviewing.
What's the best companion eyepiece?
The 10.5mm PF is the natural partner — it roughly doubles your magnification while staying in the same line and nearly parfocal. For a three-eyepiece set, add the 25mm PF for low power or the 5.5mm PF for high power. Alan Dyer's review for Cloudy Nights tested all five and called the set superb performance for the price.
Optional Accessories
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Astro-Tech PF 10.5mm 1.25" eyepiece — The medium-high power companion. Same 5-element design. Together with the 19mm, you have a two-eyepiece kit that covers most visual targets.
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Astro-Tech PF 5.5mm 1.25" eyepiece — The high-power end of the PF line. 6-element design for maximum correction. Pushes into planetary and double-star territory.
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Astro-Tech PF 25mm 1.25" eyepiece — Low-power wide-field. 4-element design. Add it to the 19mm for a two-step magnification range at minimal cost.
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Any standard 1.25" nebula or light pollution filter — Threads directly onto the eyepiece barrel. An OIII or UHC filter at 50–100x on emission nebulae can reveal structure invisible without filtration.
Final Thoughts
The 19mm PF sits in the sweet spot of the line. It has enough elements to correct the field where the simpler 25mm can't, enough focal length to keep the exit pupil comfortable in almost any telescope, and enough eye relief to work with glasses. If you own a telescope with a stock Plössl and you've been wondering what the next step looks like — more magnification, wider field, sharper edges — this is it. And if you try the 19mm and want more range, the rest of the PF line is nearly parfocal and waiting.
