Thanks to the good people at Rother Valley Optics*, I recently had the opportunity to conduct a hands-on review of Celestron’s Omni Plössl eyepieces.
I was loaned the 32mm, 15mm and 9mm eyepieces. These were all used in my 150mm (6″) SkyWatcher Newtonian. It has a focal length of 750mm making it an f/5 scope (how to calculate focal ratio).
The relatively short focal length of my telescope means that I don’t get very high magnifications, especially as I did not have the Omni Barlow lens to couple them with. Therefore, the magnifications I got were 23x with the 32mm eyepiece, 50x with the 15mm, and 83x with the 9mm.
The rest of this article goes into my impressions of these eyepieces over an evening of clear viewing.
Omni Plössl Technical Spec’s
There are seven sizes of possible eyepiece in Celestron’s Omni range. The smallest has a focal length of 4mm and the rest range up to 40mm, as seen in the table below.
Style
They all have a similar style, which you can see in the picture above. The lower half of the 1.25 inch barrel is a gloss finish aluminium, while the top half has a matte gray finish.
The 15mm and longer eyepieces each has a rubberized ring for better grip and handling. Each eyepiece in the range also has a knurled groove designed to stop the eyepiece falling out of your telescope if the holding screws are not tightened thoroughly.
I tested this and found it to be really effective; even leaving the tightening screws so loose a toddler could wobble them, the eyepieces would not fall out.
As you’d expect, all of the eyepieces in this range have a rubber eye cup which can be folded down out of the way the spectacles wearers.
Technical Design
Each eyepiece (EP) in the range consists of four glass lens elements that serve to reduce distortions and chromatic aberrations. Lenses are treated with layers of high transmission chemical coatings to improve clarity and brightness.
The four lenses are also given blackened edges, and the internal side of the barrel is similarly blackened. Both these treatments serve to reduce internal reflections, which improves the view through them for the user.
In my testing, this worked well. I tried hard to see internal reflection and did not note any even when looking at the bright moon.
This is not a ‘parfocal’ range, i.e. you will need to refocus your scope whenever you swap between different eyepieces within the range.
Eye Relief
Eye relief varies dramatically through the range. In the three models reviewed, it ranged from 6mm in the 9mm eyepiece to 22mm in the 32mm eyepiece. The 15mm eyepiece is stated to have eye relief of 13mm.
Just reading this data, you’ve probably already formed an opinion about eye relief. In the details of my review below, you’ll find the scant eye relief of the 9mm eyepiece was the biggest criticism I had.
Fields of View
The apparent field of view for the eyepieces is 50°, however, Celestron’s own website states that the 32mm eyepiece has a 44° apparent field of view. This is believed to be an error on their website.
The true field of view available to me during testing was 1.91° for the 32mm eyepiece, 1.00° for the 15mm eyepiece and 0.60° for the 9mm eyepiece.
None of these fields of view provide particularly close-up or zoomed-in views. For example, the gibbous moon I studied with the 9mm eyepiece still fit completely within my field of view. This is due to the telescope used rather than the eyepieces themselves.
The Hands-On Review
I carried out my review over two evenings, one was dark and starry, which I used to check optical clarity across the field of view, the other had a gibbous moon which I used for testing color performance.
First Impressions
First impressions are good right off the bat. The eyepieces in the range come packaged in glossy, simple but sturdy enough boxes as can be seen below.
Inside the box, the eyepiece is stored within a small Ziploc plastic bag and is capped with a snug, dust-protecting plastic cap over both the barrel and the eye lens.
There’s no arguing that these do look smart, even if not and well made with a good quality metallic finish. At the larger end, the models do feel sturdy and rigorous rather than heavy and bloated.
I found each of the other pieces easy to handle and at no point so worried that I would drop or lose them. As mentioned earlier, the anti-slip ring machine into the barrel works very well, in fact, almost too well when it delayed an easy changeover between eyepieces.
Over the next three sections, I report back on the three eyepieces individually. I’ve included the latest Amazon price within the article, and you can click this link to see the range at Rother Valley Optics.
The 32mm Celestron Omni Plössl Eyepiece
The 32mm eyepiece presents a lovely large field of view, which was almost 2° across in my telescope.
The field was lovely and clear and at its centre, stars were sharp. However, in swapping backwards and forwards between the 32mm and the 15mm models, I did perceive that the 15mm was optically the sharper of the two.
As stars moved across the field of view, there was perceptible coma (star tails) at the extreme edges, but certainly nothing so significant as to be distracting from the main show in the center. It also performed better in this regard than the 15mm and 9mm models.
Trained on our lunar neighbor, I saw a mesmerising view of the almost-full moon. Color clarity was good and optical quality was likewise high, as you can see on the picture below.
The lunar picture above was taken with an iPhone through the eyepiece which exaggerates the blue light bleed on the lower right edge of the moon. This was practically imperceptible with my eyes, even though I was trying to see it.
Eye relief was blissful, and I spent a long while following the moon without wishing to swap to another EP.
- Omni eyepieces offer a quality 4-element Plossl optical design at a super affordable price.
- Rubber eyecups provide comfort and increase contrast. Leave them up or fold them down when wearing eyeglasses.
- Beautiful matte aluminum barrels and blackened lens edges prevent internal reflections.
- 1.25” barrels are threaded to accept filters.
The 15mm Celestron Omni Plössl Eyepiece
Jumping down to the 15mm eyepiece more than halved my field of view but I still had almost one complete degree of visibility.
This time, I did notice some colour splitting out, notably yellow at the Moon’s edge. On the positive side, as noted above, I found the central area of this eyepiece to be the sharpest of all three models that were tested.
Away from the centre of view, there were increasing star trails which is to be expected but, again, nothing that would be unwelcome in a regular night’s viewing. I suspect I only noticed it because I was looking for it.
Eye relief was notably tighter, but in present a problem for general viewing. It just wasn’t as comfortable an experience as I’d had with the 32mm eyepiece. Sadly, there’s not much to be done about this because it’s just physics at play.
For me, this was the best the three eyepieces providing a sweet spot of magnification, field of view, and high quality optics.
- Omni eyepieces offer a quality 4-element Plossl optical design at a super affordable price.
- Rubber eyecups provide comfort and increase contrast. Leave them up or fold them down when wearing eyeglasses.
- Beautiful matte aluminum barrels and blackened lens edges prevent internal reflections.
- 1.25” barrels are threaded to accept filters.
The 9mm Celestron Omni Plössl Eyepiece
If the 15mm was my darling of the show, then the 9mm was my scoundrel! The reason? Simple: eye relief.
Technically, eye relief is given as a paltry 6mm, but I’m not convinced it was even that good. If you wear glasses, I’m afraid you stand no chance with this eyepiece. Even with the rubber guard rolled down, I struggled to get the whole scene into view.
What I did see was a clear area of focus at the centre of the field which quickly deteriorated at the edges. Color separation was no worse than the other two sizes, as you can see in the picture above of lunar craters.
As mentioned earlier, treat my amateur iPhone photography with a pinch of salt, the images I saw with my own eyes were substantially clearer than these cell phone pictures would lead you to believe.
- Omni eyepieces offer a quality 4-element Plossl optical design at a super affordable price.
- Rubber eyecups provide comfort and increase contrast. Leave them up or fold them down when wearing eyeglasses.
- Beautiful matte aluminum barrels and blackened lens edges prevent internal reflections.
- 1.25” barrels are threaded to accept filters.
Summary
Overall, I found the Omni EP range to be overall fantastic quality, particularly given the relatively the relatively low cost of each eyepiece.
They look professional and well made, feel great in the hand and are simple to use.
The longer focal length pieces performed really well. I didn’t perceive any internal reflection, coma was limited to the outer edges of the field and color separation was limited.
The 9mm model was the weakest of the set, principally because its eye relief was too poor to be useful (I’m not the first to say this). Its optical quality was also the poorest of the trial set. While it still performed well, it was notably worse than either the 32mm or 15mm models.
If you’re on a limited budget and are looking for a cheap but effective way to improve the quality of your telescope viewing, you’ll be hard pushed to do better than investing in the Omni Plössl range, although you may want to stick to the higher focal lengths.
Rother Valley Optics is a renowned UK-based optical retailer. They sell a massive range of astronomy products from filters to telescopes and, with over 12 years’ trading experience, pride themselves on their honest, useful advice.
My thanks to them for the equipment loan. Check them out for yourself here.
*Rother Valley Optics neither sponsor nor have editorial control over this post. We do not receive any commission payments from RVO.
Last update on 2023-12-08 / Affiliate links / Images from Amazon Product Advertising API
