Comprehensive Evaluation of Celestron Luminos Eyepieces: Worthy Recommendation

Comprehensive Evaluation of Celestron Luminos Eyepieces: Worthy Recommendation

Unfiltered Scoop on Celestron's Luminos Eyepieces

Hey astronomy aficionados! Let's dive into an in-depth review of the Celestron Luminos eyepieces, those ultra-wide-angle fellas that have been stealing the show for a while now. Despite facing stiff competition, Luminos remains a decent choice for UWA (Ultra-Wide Angle) design enthusiasts.

Available in six distinctive focal lengths – 2" barrel 31mm, 23mm, and 19mm, as well as 1.25" 15mm, 10mm, and 7mm units – these bad boys offer a wide range of viewing options.

Celestron also sells a 2.5x, 2" Luminos-branded Barlow lens. While it's a solid Barlow, we probably wouldn't recommend it due to its hefty weight and the overall lack of a strong reason for investing in a 2" Barlow lens.

Which Luminos Eyepiece To Grab?

The 31mm Luminos is on the heavy side and shows some edge-of-field brightening, but it provides nearly the greatest true field achievable with a 2" eyepiece, making it the best pick of the 2" Luminos lineup. We'd advise skipping the 23mm and perhaps the 15mm, while the 10mm and 7mm eyepieces have few flaws, and the 19mm is acceptable. The 10mm Luminos is hands down the best of the bunch and an excellent choice for medium to high-power observations.

Luminos Eyepieces: Optical Design and Performance

The Celestron Luminos eyepieces follow, more or less, the well-known Tele-Vue Nagler optical design. The claimed field of view is 82 degrees, and it's right around that mark in reality. The principal difference between Luminos and other UWAs is that it features an unusual property called angular magnification distortion.

For instance, the field stop of the 23mm Luminos has a 37mm diameter, which translates to a 92-degree apparent field. However, the magnification of the eyepiece decreases as you move along the edges of the field of view – a type of extreme field curvature, essentially. This results in two factors – the apparent field remains 82 degrees, and the edges of the field are essentially squashed gradually, up to 26% in the case of the 23mm Luminos. This phenomenon is known as "angular magnification distortion." However, you're unlikely to notice the curvature as much as the edge-of-field brightening.

Because the magnification of the Luminos eyepieces is lower at the edges compared to the center, the night sky appears brighter as a result. This is a common complaint amongst users.

However, you will only notice this under moderately light-polluted skies while observing deep-sky objects at low power without a filter. Darker skies reduce the effect, while severe light pollution turns the background so bright that the subtle brightening is not significant. High-power settings dim down the background so much that a slight increase in brightness is insignificant. The edge-of-field brightening is due to a mix of sky background brightness amplified by internal eyepiece reflections.

You won't see edge-of-field brightening at all if you have dark skies or heavily light-polluted skies or are using a Luminos eyepiece with a telescope that produces an under 3mm exit pupil (or around 8x per inch of aperture), or are looking at a bright target, or if you are using a narrowband nebula filter.

The 10mm and 7mm Luminos eyepieces don't meet Celestron's stated specs and seem to be manufactured by Kunming United Optics, using identical optics to the UWA eyepieces sold by Astro-Tech, Meade, AngelEyes, and others. The 10mm Luminos has essentially no angular magnification distortion and, thus, no edge-of-field brightening.

The table below shows the parameters of each eyepiece, as well as the specs for angular magnification distortion. The severity of edge-of-field brightness is calculated based on the background sky brightness and angular magnification distortion in a given telescope, relative to what the 23mm Luminos would show. The 31mm Luminos has lower angular magnification distortion compared to the other eyepieces in the lineup, but its lower magnification makes edge-of-field brightening more noticeable.

These calculations align well with observations through all the Luminos focal lengths tested across telescopes of different optical designs and focal ratios. As you can see from the table, despite the 7mm Luminos' massive angular magnification distortion, the edge-of-field brightening is minimal, and the 35% field curvature is only mildly perceptible. The 19mm is actually the least offensive of all the Luminos low-power eyepieces, but it seems to catch a lot of unnecessary flak.

All Luminos eyepieces perform well across any focal ratio, with the only aberrations being field curvature and minor lateral chromatic aberration. However, edge-of-field astigmatism may become visible in telescopes faster than around f/4.5 with all Luminos eyepieces, even with a coma corrector.

Mechanics

The Celestron Luminos eyepieces boast a robust, wide metal housing with a rubber grip ring. Twisting this ring adjusts a twist-up eyecup, similar to the old Meade Series 5000 UWAs, but with a twist – rather than twisting the entire eyecup, you simply rotate the ring. It's not the most intuitive design but works effectively, and the eyecup is extremely comfy once you've got it set right. However, the design adds width and weight.

An important thing to remember about the Celestron Luminos eyepieces is their hefty bodies and twist-up eyepieces can be removed via "decloaking," a process that requires some DIY finesse and a desire to minimize weight or volume. If you'd like to use the 1.25" 15mm, 10mm, or 7mm Luminos eyepieces in a binoviewer, this is usually not possible due to their width – decloaking is a great workaround for this issue.

Alternative Choices

Instead of the Luminos lineup, you may wish to consider other UWA options:

• The Meade PWA and Astro-Tech UWA eyepieces outperform the Luminos eyepieces at their longer focal lengths, though the 10mm and 7mm units are identical optically.
• The Baader Morpheus eyepieces feature a mere 76-degree apparent field but offer extremely sharp, high-contrast views with plenty of eye relief.
• The Explore Scientific 82-degree line offers a few excellent units, some with edge-of-field brightening/AMD, and others with too-short eye relief, but most don't disappoint and often rival the Tele-Vue Naglers in performance.
• The Tele-Vue Nagler lineup boasts decent eye relief, sharpness, few aberrations, and better optical coatings than any of the other UWA eyepieces – but the price is, of course, on the steep side.

1. For those interested in expanding their home-and-garden, home-theater, or gadgets collection, the Celestron Luminos eyepieces could be a unique addition, providing a wider field of view for telescopes.
2. Considering lifestyle factors, the Luminos eyepieces might not be the ideal choice for astronomy enthusiasts living under moderate light pollution, as they exhibit edge-of-field brightening when observing deep-sky objects at low power without a filter.
3. Technology enthusiasts might find the mechanics of the Celestron Luminos eyepieces intriguing, with their robust metal housing, twist-up eyecup, and unique design, even though it may add weight and volume.
4. In the field of optics, the Luminos eyepieces, while showing optical distortion and edge-of-field brightening under specific conditions, perform well across any focal ratio, outperforming other UWA options in some aspects, such as field curvature and lateral chromatic aberration.

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