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19mm Celestron Luminos/18mm Explore Scientific

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#1 Shorty Barlow

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Posted 06 June 2020 - 09:54 AM

I love my 19mm Celestron Luminos. Yes, admittedly, the entire series has various peculiarities that irritate many people. These include: edge astigmatism, edge of field brightening, ghosting, glaring, inter alia. Notwithstanding the twist-up eyeguard and its heavy shroud mechanism. Even with these shortcomings I still enjoyed using the Luminos as a rich field eyepiece, especially in my Evostar 72ED DS Pro. 

 

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The 82° field of view together with a large accommodating eye lens and with a huge 30mm field stop gave a stunning 22.1x for a 3.2mm exit pupil. The 20mm eye relief made it ergonomically pleasant and physically undemanding to use. Especially if you are standing to observe and sweeping the night sky. However, there was one huge drawback; it is bloody heavy! I make it 460g with my kitchen scales. The main complication with this weight was in using the ED72 on a Vixen Porta II mount. The Porta altitude clutch had to be set tight enough for there to be no drift, yet loose enough to be able to switch to a lighter 1.25” diagonal for higher magnifications. The ED72 can have in-focus problems with 2” diagonals and shorter focal length eyepieces.

 

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My first instinct was to eschew the 2” Baader dielectric for the Baader 1.25” Amici and use my 19mm Tele Vue Panoptic instead. This would seriously improve the weight situation, bearing in mind I'm partially paralysed in my right arm and hand. The 19mm Panoptic is one of my all time favourite eyepieces. As brilliant as it is, it isn't 2" though, and I really prefer 2" eyepieces for rich field observing.

 

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There was a viable alternative. The 2”, 18mm Explore Scientific has some similarities to the Luminos. Although the eye lens and eye relief are respectively smaller and shorter, the eye relief being 7mm less and the field stop is only 25.3mm. There are advantages however. I make it 370g, considerably lighter than the Luminos. The barrel plays nicer with the Baader twist-lock, the flip-up rubber eyeguard is reassuringly simpler and I believe the eyepiece features Lanthanum glass elements. On May the 29th I got first light with the ES 18mm. I’d waited several months for this eyepiece and actually ordered it the previous summer.

 

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I spent a good 90 minutes solely with the 18mm ES, much of it around and in a rising Summer Triangle. The closer eye relief didn’t bother me, although I wasn’t originally impressed with the field of view in daylight tests with my ED80. It seemed visually claustrophobic in an f/7.5 doublet. This eyepiece seems better suited to faster scopes in my opinion.

 

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In the ED72 the field seems large enough and with no astigmatism that I could detect. The image was bright and sharp. I easily found both globular clusters in Hercules at 23.3x and even got a hint of M57. The 18mm ES is definitely a keeper and the 19mm Luminos can be used with the ED80.

 

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#2 ValhallaObserver

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Posted 06 June 2020 - 11:42 AM

This looks to be a wonderful eyepiece. Have you tried it in your Celestron SCT and other larger refractors? If so how does it perform. I would think even better at longer focal length scoped.

 

VO



#3 Shorty Barlow

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Posted 06 June 2020 - 12:35 PM

The SCT doesn't get out much, and when it does I only use 1.25" diagonals, although I plan to use 2" in the future with it. I've not tried either the Luminos or ES in my 102mm Starwave yet. The Luminos is definitely better in slower scopes. I wasn't over keen on the ES 18mm in anything slower than f/5.8.


Edited by Shorty Barlow, 06 June 2020 - 12:35 PM.


#4 Dave Bush

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Posted 06 June 2020 - 04:05 PM

If you ever get a hold of a 19mm Axiom LX you’ll no longer like your Luminos. 



#5 Shorty Barlow

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Posted 06 June 2020 - 04:56 PM

If you ever get a hold of a 19mm Axiom LX you’ll no longer like your Luminos. 

I've heard this before. As far as I can ascertain the Axiom LX series were more like the ES 82° eyepieces than the Luminos anyway. The 19mm Axiom LX has a smaller eye lens than the equivalent Luminos which is indicative of a quite different design. The Axiom eye relief was also nearer the ES 82° series. In fact it is probably far more like the ES 18mm than the Luminos.

 

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Above ~ picture of 19mm Axiom LX

 

The 19mm Luminos is a very ergonomically pleasant eyepiece to use in my experience. I'd still be using it in my ED72 if it wasn't so heavy. An Axiom equivalent would almost certainly be the same weight. A lot of that weight is probably the shrouding mechanism for the eyeguard. The 19mm Axiom also probably doesn't have the same ergonomic feel as the Luminos.

 

I can live with the EOFB and the edge astigmatism of the Luminos, I can't live with its weight. It's 90g heavier than the ES18mm. It might not sound like a lot but it makes a big difference on the Porta II.

 

The Luminos is fine on slower scopes. I like it on the ED80. The ES 18mm was not as comfortable on the ED80 and the field seemed quite diminished compared to the Luminos. For rich field viewing I find comfort is an important factor. If I have to push my eye right up against the eye lens and squint into the eyepiece it diminishes the observing experience for me. If I'm not comfortable I'm not observing well.

 

Luckily the ES 18mm seems to solve the problem in the ED72.


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