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Astro-Tech PF Eyepieces Review: Excellent Performance, Affordable Price

The new PF series of eyepieces from Astronomics’ house brand Astro-Tech proves to be a fine choice for anyone wanting to upgrade their beginner telescope’s eyepieces.

 

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In Astro-Tech’s new PF series, the 19mm, 15.5mm and 10.5mm (the middle trio) are five-element designs. The 25mm (at far left) has four lens elements, while the 5.5mm (at far right) has six.  Credit: Alan Dyer

 

Entry-level telescopes often come with notoriously bad eyepieces plagued with narrow fields of view, false color fringing, and short eye relief making them difficult to look through. Views can be fuzzy, and in a tunnel-vision field of view.

Or a telescope might be supplied with only one eyepiece. While it might be a decent quality Plössl type, it yields only a one low magnification, typically around 25x. Good views of details on the Moon and planets, the very targets beginners most want to look at, require a high-power eyepiece, one yielding about 125x to 175x. Many deep-sky objects, like nebulas and galaxies, are best viewed at a medium power of about 50x to 100x.

 

If your entry-level telescope uses one of these types of economy eyepieces, you’re in the market for an upgrade! Some of these are good only for use as dust caps. Credit: Alan Dyer

 

So new telescope owners can be faced with the immediate need to purchase additional eyepieces to ether expand the range of magnifications or improve the views or both. The problem is, taking the next step up in quality for a good eyepiece set can cost as much as, or more than, the original telescope.

Astronomics’ new Astro-Tech PF series addresses this issue by offering eyepieces with attractive specifications for only $55 per eyepiece. Adding two or three to fill out a range or to replace lesser quality eyepieces will still cost less than a good beginner scope. But will the upgrade be worth it? To find out, I tested a set of all five PF eyepieces on loan from Astronomics.

 

Optical Quality 

I tested the PF set on four typical beginner scopes: a 70mm f/9 refractor, an 80mm f/10 refractor (both achromats), a 130mm (5.1-inch) f/5 Newtonian reflector, and a 150mm (6-inch) f/10 Schmidt-Cassegrain. As a further check, I also tested them on my “reference standard” for superb optics, the legendary Astro-Physics 105mm Traveler “apo” refractor.

 

This compares the relative amount of sky each class of eyepiece will reveal when used on the same telescope. While each will provide about the same magnification, the lesser eyepieces provide much narrower fields than a wide-field eyepiece like a PF. Credit: Alan Dyer

 

The specification that stood out for me is the PF’s stated apparent field of view (AFOV) of 65° for the 25mm, 19mm and 15.5mm models, and 60° for the higher-power 10.5mm and 5.5mm models. AFOV is the angular diameter of the circle of light you see when holding the eyepiece up to the light. The wider the AFOV, the more panoramic the viewing experience. An AFOV of 65° puts an eyepiece into the wide-field category, and even 60° is still wider than the narrow 30° to 45° fields of most low-cost eyepieces. (Budget Plössls, though capable of providing sharp images, typically have 50° fields at best.) 

The 15.5mm exhibited the widest AFOV, matching the field of other 65° eyepieces in my collection. The 25mm and 19mm had slightly smaller AFOVs, but still wider than the 60° 10.5mm. The 5.5mm, while also marked as having a 60° AFOV, appeared to match the 65° field of the 15.5mm. In all the PFs, the dark edge of the field was sharply defined, not fuzzy as in some eyepieces.

Though some of the numbers did vary a little from spec, all the PFs provided a more impressive viewing experience than the just adequate three-element Kellner (Ke) and simply awful two-element Huygenian (H) eyepieces often supplied as standard accessories.

The most notable improvement was on the Newtonian reflector, a Celestron Astromaster 130EQ. The 20mm Erect-Image eyepiece supplied with the Astromaster for low power use is about the worst eyepiece I have ever seen supplied with a beginner scope. Swapping it for the 25mm PF is like removing blinders and a gauzy veil — the view sharpens, brightens, and widens. 

 

The PF series all have tapered 1.25-inch barrels threaded to accept standard filters, popular accessories for enhancing views of the planets and deep-sky objects. Credit: Alan Dyer

 

The other promise of performance is embodied in the series name, PF, which stands for Premium Flat, suggesting images will appear sharp across the entire field, from edge to edge. 

With all the telescopes tested, this promise came very close to being fulfilled. Planets and stars softened only in the outer 10% to 15% of the field (i.e., at the very edge), primarily in the three longer focal length PFs. At the edge, stars showed little wings from astigmatism and some color fringes from lateral chromatic aberration. The edge performance was worse in the fast f/5 reflector where its inherent coma became apparent in the low-power eyepieces, flaring stars at the edge a little more than in the slower f-ratio refractors and in the Schmidt-Cassegrain.

However, across most of their fields, images in all the PF eyepieces proved to be very sharp and completely free of any false color fringing and annoying ghost images on bright objects like Jupiter.

 

The PF’s lenses all appear to be fully multi-coated. The eye lenses, even in the shortest focal lengths, are large and easy to look through. Credit: Alan Dyer

 

Eye relief is stated as being at least 16mm even for the high-power 5.5mm, and as long as 23mm for the 25mm PF. As measured from the top of the eye lens, the figures proved accurate, making even the 5.5mm quite comfortable to look through, though its small exit pupil demands your eye be exactly centered to see the whole field.

For eyepieces costing only $55, yet with apparent fields as wide as 60° to 65°, this was superb performance. The eyepieces just got out of the way for a fine viewing experience.

 

Each PF comes well packed in a foam-lined but plain box. Each includes a lens cleaning cloth but nothing as luxurious as a case or pouch. Credit: Alan Dyer

 

Physical Features

The PF eyepieces feature attractively machined and black anodized barrels, all with a tapered cut to prevent their falling out of a focuser or star diagonal. They all have rubber grip rings and a red trim ring with the labeling.

My only criticism is that the focal length should be in lettering at least as large and as bold as the brand name to make it easier to identify the eyepieces in the dark under red light. 

The eyepieces are almost parfocal, with the 10.5mm requiring the most refocusing when switching eyepieces, though still by only a minor amount.

 

The eyecups can be pulled off (as at left). They fold down easily (as at right) to allow viewing the entire field with glasses on, even of the 5.5mm model. Credit: Alan Dyer

 

The rubber eyecups, a feature not found on many low-cost eyepieces, clip on. They stayed firmly in place even when rolling them up and down. Being rubber, they should stand up to use and not become brittle and crack over time.

 

Recommendations

If you have eyepieces from the lower class of designs, there is no question that upgrading to a set of PF models will improve the view. Images will be sharper across a wider field, with the longer eye relief making moderate to high-power views more comfortable.

However, you certainly don’t need all five PF eyepieces. The 25mm, 10.5mm and 5.5mm will make a good set for most small beginner scopes, providing low, medium, and high powers. Remember the “Astro 101” formula — the power an eyepiece provides on a telescope is equal to the focal length of the telescope divided by the focal length of the eyepiece (using the same unit of length for both).

 

A nice touch is that all the PF eyepieces share the same top and the same bottom caps, eliminating fussing in the dark to find the right end caps. The caps are made of flexible rubber. Credit: Alan Dyer

 

It’s a pity there isn’t a 7mm PF between the 10.5 and 5.5mm eyepieces, as it would be a better choice for high-power use on telescopes with focal lengths longer than 800mm. For example, the 5.5mm yields 275 power on the 6-inch f/10 Schmidt-Cassegrain (with its 1500mm of focal length), too high for sharp views on most nights. A 7mm would provide a more useful top power of 214x, to complement the 25mm and 15.5mm models for a useful trio.

 

Astronomics’ series of UWA eyepieces, with their 82° apparent fields, represent the next step up in eyepiece quality in their house-branded Astro-Tech line. Credit: Alan Dyer

 

That said, if you are in the market for a viewing experience better than the PF series provides, consider Astro-Tech’s next series up in specifications, their 82°-wide UWA eyepieces. I was sent a sample 10mm UWA to complement the 4mm UWA I purchased earlier in 2022, which I tested here for AstroGearToday. At $99.95 for each of the 1.25-inch models in the UWA line, they represent a terrific buy for 82° eyepieces.

To conclude, I have been impressed with the new and very affordable eyepieces Astronomics has introduced in recent months. They all provide great values. I highly recommend them.

 

Plus

Very sharp images free from false color

Wider fields than most low-cost eyepieces

Excellent eye relief

Flexible rubber eyecups

 

Minus

Minor edge-of-field aberrations

Labeling hard to read at night 

Series lacks a 7mm eyepiece

 

MSRP: $55 each

Website: www.astronomics.com

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About Alan Dyer

Alan Dyer is an astrophotographer and astronomy author based in Alberta, Canada. His website at www.amazingsky.com has galleries of his images, plus links to his product review blog posts, video tutorials, and ebooks on astrophotography.

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