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Celestron Xcell LX: 2.3mm vs 5mm + Barlow x2

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#1 Astroyesmer

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Posted 22 September 2022 - 05:01 AM

I have a  Celestron Xcell LX 5mm that I use for planetary, and it is quite a good piece of glass. It is said here and there that it is closer to 4.6mm than 5mm, but the wide fov and comfortable ER are very nice.

 

When seeing conditions are great I use a 2x barlow (Celestron Omni) and I was wondering if this configuration brings the same visual results than using the 2.3mm Xcell LX, or if it was worth ordering the latter to give it a shot.

 

Since the 2.3mm and the 5mm are built with the same amount of glass, and since there is one more piece of glass with the barlow, is it fair to assume that at this very high magnification the 5mm + barlow would produce more blur than the sole 2.3mm EP?

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Edited by Astroyesmer, 22 September 2022 - 05:02 AM.


#2 Nicole Sharp

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Posted 22 September 2022 - 05:41 AM

I would be very curious to hear the difference, if any, between the 2X Barlow with the 5-mm eyepiece versus the 2.3-mm eyepiece.  The effective eyepiece focal length is slightly different though, at 2.5 mm versus 2.3 mm.  The only advantage I think of the additional eyepiece is that it will be parfocal with the other X-Cel LX eyepieces, whereas a Barlow will require refocusing.

 

But if you use the Barlow for other eyepieces, it might be worth upgrading the Barlow lens instead of adding a high-power eyepiece that you might only be able to use under very good seeing conditions (if you don't mind refocusing).  Upgrading to an apochromatic 3-element Barlow like the Celestron X-Cel LX or a 4-element focal extender like from Explore Scientific could improve your views compared to using a 2-element achromatic Barlow.

 

Refocusing could be problematic at the very high magnification though so the parfocal eyepiece is probably the easier option.  What would be better is to just keep the Barlow in place, and then use the various parfocal eyepieces without removing the Barlow lens, negating the need to refocus or have the 2.3-mm eyepiece.


Edited by Nicole Sharp, 22 September 2022 - 05:49 AM.


#3 Astroyesmer

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Posted 22 September 2022 - 08:21 AM

The thing is, it seems that the actual focal lenght of the so called 5mm is actually 4.6mm, from infos I gathered through some cloudynights threads, making the 2.3mm exactly the same as the 5mm with a barlow - aside of course the barlowing...

I wouldn't mind upgrading the omni barlow with the Xcell barlow, I am just not so sure it would be such an improvment glass wise?
But I already own the Xcell 3x barlow and the Luminos 2.5x barlow, so I'd rather know where I am going before ordering...

2.3mm with 60° fov seems like a sweet spot for Saturn under great skies, and I'm mostly curious about the actual improvment at such high mag with the 2.3mm EP vs the 5mm EP barlowed...

#4 Transmaniacon

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Posted 22 September 2022 - 08:42 AM

What is your telescope aperture?  2.3mm will lead to pretty high magnification that you may not be able to take advantage of due to the atmosphere.



#5 firemachine69

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Posted 22 September 2022 - 08:53 AM

The benefit (or hindrance) is exit pupil size, depending on the scope.

 

 

My eyepiece case at home currently has the full ES82 series and a singular 3mm ES52.

 

The 3mm, 4.7mm, and 6.7mm see zero use because the conditions around here largely preclude any levels of high magnification. However a little while ago, I owned an 80mm fast apo (500mm FL), which saw significant use with those eyepieces. Well, almost all of them, the 3mm is still a hot piece of garbage. lol.gif



#6 Astroyesmer

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Posted 22 September 2022 - 11:35 AM

The benefit (or hindrance) is exit pupil size, depending on the scope.

 

 

My eyepiece case at home currently has the full ES82 series and a singular 3mm ES52.

 

The 3mm, 4.7mm, and 6.7mm see zero use because the conditions around here largely preclude any levels of high magnification. However a little while ago, I owned an 80mm fast apo (500mm FL), which saw significant use with those eyepieces. Well, almost all of them, the 3mm is still a hot piece of garbage. lol.gif

Wouldn't the exit pupil of the 2.3mm EP be the same as the 4.6mm EP with barlow x2 anyway?

 

What is your telescope aperture?  2.3mm will lead to pretty high magnification that you may not be able to take advantage of due to the atmosphere.

 

102mm. I already know there is no problem with this magnification since the 5mm (4.6mm in fact) EP with the 2x barlow gives good views (Saturn/Jupiter/Mars)... but would the plain 2.3mm EP look better/clearer/crispier is the question :)



#7 Dobs O Fun

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Posted 22 September 2022 - 12:30 PM

What is your telescope aperture? 2.3mm will lead to pretty high magnification that you may not be able to take advantage of due to the atmosphere.


That's been my issue at 1200mm. I have the 5mm and seeing is greatly affecting me.

#8 vtornado

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Posted 22 September 2022 - 05:17 PM

I would not expect a large increase in clarity between a 5mm barlowed and a native 2.5mm eyepiece.  Barlows can add to scatter.  I have a GSO 2x, I have to strain my eyeballs to notice that it is in the optical train.

 

Also in the mix is that is a 2.5mm xcel-x as good as a 5.0mm xcel-x

most eyepiece families have some members that are not as good as others.

 

You don't mention the focal length of your scope.


Edited by vtornado, 22 September 2022 - 05:21 PM.

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#9 CeleNoptic

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Posted 23 September 2022 - 03:02 AM

The thing is, it seems that the actual focal lenght of the so called 5mm is actually 4.6mm, from infos I gathered through some cloudynights threads, making the 2.3mm exactly the same as the 5mm with a barlow - aside of course the barlowing...

 
Where did you get this number, could you provide the reference? The 5mm X-Cel LX is most probably a rebranded 4.5mm Meade HD-60. Plus, keep in mind that telenegative Barlows magnification factor usually doesn't match the claimed one and slightly varies for different eyepieces. If you want precision you should test it for each eyepiece combination. Your 2x Omni most probably works at 2.1-2.2x with most eyepieces so combined with the 4.5mm eyepiece it'll give something closer to 2.1-2.0mm and it's quite a difference vs 2.3mm. IMO, the 2x Celestron X-Cel LX should be a nice upgrade over the 2x Omni. Like you I have the 3x X-Cel LX and it shows excellent light scatter control, better than cheaper Barlows e.g. GSO etc.



#10 Astroyesmer

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Posted 23 September 2022 - 03:35 AM

I am not sure but there was an extensive topic on Cloudy Nights where the guys reviewing the Xcell precisely measured it and came to the conclusion the EP was in fact 4.6mm. The topic is arpund here somewhere I just don't have the link presently. 

 

The Omni barlow is nowhere near bad, and have the removable nosepiece like the baader Q that allows a smaller magnification around 1.5x...

 

I guess the only way to find out about my OP is to order a 2.3mm EP and compare the crispiness with the 5mm + barlow; I just thought there might be people around here that own the full Xcell LX set of EPs, and colld tell how the 2 set ups compare.



#11 sportsmed

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Posted 24 September 2022 - 07:59 PM

I have used some of the X-Cel LX EP's with a GSO APO 2.5x barlow and they did well, I believe the GSO barlow and X-Cel LX 2x barlow are considered better barlows then the Omni. So if you think you might want to continue to use barlows I would upgrade personally just to have a better optical path. But saying that I dont think you will see a huge difference with the barlow and 5mm or just the 2.3mm. I guess it really matters on do you mind having to use a barlow to view or just throw in a single EP and enjoy the view when conditions are right.



#12 firemachine69

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Posted 24 September 2022 - 08:18 PM

Wouldn't the exit pupil of the 2.3mm EP be the same as the 4.6mm EP with barlow x2 anyway?

 

 

102mm. I already know there is no problem with this magnification since the 5mm (4.6mm in fact) EP with the 2x barlow gives good views (Saturn/Jupiter/Mars)... but would the plain 2.3mm EP look better/clearer/crispier is the question smile.gif

 

I'm still rather curious what scope you're using that can support such a short focal length. My old 80mm / 660mm apo was rarely being used with anything shorter than a 4mm ish focal length, and the glass was rather exceptional on it. 



#13 Astroyesmer

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Posted 25 September 2022 - 03:37 AM

A 4" achro. F/6.5 (660mm 102mm)

Like I said for Jupiter and Saturn, and sometimes Mars, I can barlow 5mm 2 to 3 times and still see details although more or less dim depending of the atmosphere.

With a 4mm barlow it is a struggle (shakes and object hard to follow) but with 2.3mm 60° fov it is actually quite a piece of cake.

The OTA is a Celestron Starsense 102DX.

#14 vtornado

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Posted 25 September 2022 - 04:59 PM

Hmmm 100mm achro in midwest seeing.  I would choose something that gives you around 150x. 4-5 mm.

a lot determines if your eye/brain system prefers a smaller/brighter image vs. a larger dimmer image.

 

Wratten #8 might tamp down a bit of the CA but again a personal preference.


Edited by vtornado, 25 September 2022 - 05:04 PM.


#15 Astroyesmer

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Posted 25 September 2022 - 05:25 PM

Well I usually keep above 4mm but, like I said, some nights with great seeing conditions allow for way more magnification on bright objects with surprising results...

 

 

Hmmm 100mm achro in midwest seeing.  I would choose something that gives you around 150x. 4-5 mm.

a lot determines if your eye/brain system prefers a smaller/brighter image vs. a larger dimmer image.

 

Wratten #8 might tamp down a bit of the CA but again a personal preference.

What do you mean by midwest seeing?



#16 vtornado

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Posted 25 September 2022 - 05:34 PM

Where I live which is northeast Illinois, and other areas in the Midwest have no big heat sinks, like the coast.

There is typical mixing of cold Canadian dry air with hot moist gulf air.  this leads to turbulent air. 

This is much like looking through a mirage over a road on a hot summer's day.



#17 Astroyesmer

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Posted 25 September 2022 - 05:41 PM

Oh yes I see. Well yes I have experienced "moving waves" of atmosphere more than a few times in Wisconsin, especially while observing Saturn. But most of the time I don't experience them. I usually observe from 10pm to 4am, and frequently from Door County dark sky area...



#18 Astroyesmer

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Posted 25 September 2022 - 05:47 PM

About this thread I came to the conclusion the 2.3mm EP was not a necessary purchase. 5mm with barlow X2 will do, and I purchased a 7mm Luminos instead of the 2.3 Xcell. With my X2.5 luminos barlow this EP will allow for a 2.8mm focal lenght with the benefit of a much wider angle, useful at that magnification to keep Saturn in the EP way longer.



#19 CeleNoptic

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Posted 26 September 2022 - 02:03 AM

About this thread I came to the conclusion the 2.3mm EP was not a necessary purchase. 5mm with barlow X2 will do, and I purchased a 7mm Luminos instead of the 2.3 Xcell. With my X2.5 luminos barlow this EP will allow for a 2.8mm focal lenght with the benefit of a much wider angle, useful at that magnification to keep Saturn in the EP way longer.

 
Once again. The 2.5x Luminos isn't a telecentric Barlow so the magnification factor not necessary matching the claimed  one. You might be surprised, but it can work e.g. as 2.3x or maybe 2.7x with different eyepieces. To be sure you have to test each specific eyepiece+Barlow combination (via star timing or "ruller on the wall" methods).


Edited by CeleNoptic, 26 September 2022 - 02:04 AM.


#20 Astroyesmer

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Posted 26 September 2022 - 03:32 AM

Ok thanks for the info. Honestly that is not really an issue to me. Maybe one day this winter I will be bored on a snowy day and will test this with all my barlows through the window, daytime.

If I barlow 7 and end up with either 2.6 or 2.8 or 3 the difference will not be overly annoying!


Edited by Astroyesmer, 26 September 2022 - 03:32 AM.



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