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Luminos 2.5X Barlow and AP BARCON magnification values

Celestron Eyepieces
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#1 GGK

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Posted 01 July 2022 - 06:40 PM

I purchased the Celestron 2.5X Luminos 2-inch Barlow because of its light weight and smaller size, and I've been using it for the past two months. 

 

Performance has been quite good for me and it's working well with the Ethos, Leica, and long focal length XW eyepieces to give magnification values that I can't get with my current eyepieces alone.

 

This post is only to show the magnification values I get in different configurations. More information about the Luminos Barlow can be read in this archived thread:  https://www.cloudyni...centric-barlow/

 

I'm also including values I get with the AP BARCON screwed onto the end of the eyepiece as noted, because that also gives useful results when minimizing the number of eyepieces carried out.

 

ETHOS

First, please note that I have a Tele Vue 30mm 2" barrel extender on the 6mm, 8mm, 10mm, and 13mm Ethos eyepieces to cover the 1-1/4 barrel that extends beyond the 2" barrel.  When using Ethos with the Luminos Barlow, the barrel extender prevents the 1-1/4 barrel from contacting the Barlow lens.

 

Inserting the Ethos with 30mm barrel extender into the Luminos 2.5X Barlow results in different power factors for 6mm / 8mm Ethos vs. 10mm / 13mm Ethos due to the focal plane position. 

  • 2.26X magnification increase in the 6mm and 8mm Ethos
  • 2.46X magnification increase in the 10mm and 13mm Ethos

Therefore, the 6mm, 8mm, 10mm, and 13mm Ethos with the Luminos Barlow gives 2.7mm, 3.5mm, 4.1mm, and 5.3mm, all at 100o AFoV.  I find the Barlowed 8mm Ethos perfect for my TV-85 f/7 refractor, because it results in a 0.5mm exit pupil at 100o AFoV.

 

To attach the AP BARCON lens cell to the end of the eyepiece typically requires a 10mm M48 extension to be added to the BARCON to extend the M48 threads out beyond the T2 threads.  However, attaching the BARCON to the Ethos requires a minimum 20mm M48 extension tube.  I do not use the 30mm TV barrel extender because in this situation, I want a short path to reduce the power factor of the BARCON, so 20mm it is. The power factor is different for the 6mm / 8mm vs. the 10mm / 13mm due to the focal plane position as mentioned above.

  • 1.19X magnification increase in the 6mm and 8mm Ethos attaching the BARCON to the Ethos with a 20mm tube M48 extension
  • 1.30X magnification increase in the 10mm and 13mm Ethos attaching the BARCON to the Ethos with a 20mm tube M48 extension

Therefore, the 6mm, 8mm, 10mm, and 13mm Ethos with the BARCON and 20mm extension tube screwed onto the Ethos directly gives 5mm, 6.9mm, 7.7mm, and 10mm.  For me, the 6.9mm is a nice split between the 6 mm and 8mm Ethos.  The 5mm, is a slight bump up from the 4.7mm Ethos eyepiece if needed.

 

Note that my 20mm tube extension doesn't fully seat into the eyepiece, so some minor variance is likely with different brand extensions.

 

I find that the Luminos Barlow is more convenient to use than the BARCON because I don't need to screw anything onto the eyepiece - just slip it in. 

 

LEICA ASPH ZOOM

Adding the Luminos Barlow to the Leica ASPH Zoom with the Starlight 2" adapter increases magnification by 2.55X, for a resulting 3.5mm - 7mm zoom, with the 3.5mm end being at 75o AFoV.  This is a nice complimentary range to the Leica 1.8X Extender,  and I use them both.

 

Pentax XW 40mm

Adding the Luminous Barlow to the 40mm Pentax XW results in a 2.51X magnification increase, or a resulting 16mm focal length at 70o AFoV.  

 

Adding the AP BARCON cell to the end of the 40mm Pentax XW using a 10mm M48 extension tube increases magnification by 1.43X resulting in 28mm focal length at 70o AFoV.

 

When minimizing eyepieces with my AT60ED f/6 refractor for travel, but having enough room for two larger eyepieces (rather than Delites) and the Barlows, the 40mm Pentax XW and Leica ASPH Zoom with the BARCON, Luminos Barlow and Leica Extender provide everything from low power 7.4o TFoV up to 102X at 0.74o TFoV, which is getting close to the power limits for the small scope.

 

In the Ethos line, the Luminos and BARCON options enable me to reach many intermediate focal lengths while maintaining the 100o AFoV.

 

I still prefer the ease of using separate eyepieces without a Barlow, but it's very nice to have the optional focal lengths when wanted. 

 

Final note -- my measurements are accurate enough for me, but might vary a percent or three from actual, so if precision is needed, please remeasure with your equipment.

 

Gary


Edited by GGK, 01 July 2022 - 06:53 PM.

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#2 25585

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Posted 02 July 2022 - 08:08 AM

Very useful to know, thank you.



#3 Echolight

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Posted 02 July 2022 - 07:52 PM

The Luminos 2.5x works great with the Baader zoom!

 

9D9D327B-F38F-45E6-A56A-63B4922B41EE.jpeg

 


Edited by Echolight, 02 July 2022 - 08:08 PM.

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#4 25585

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Posted 03 July 2022 - 04:59 AM

The 2.5x is a neat bit of kit. I bought one instead of a 3x ES Barlow extender, and like my 1.6x Antares lives in the eyepiece bag.


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#5 Jon Isaacs

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Posted 03 July 2022 - 06:28 AM

Final note -- my measurements are accurate enough for me, but might vary a percent or three from actual, so if precision is needed, please remeasure with your equipment.

 

 

Gary:

 

I read your post carefully but I could not see an explanation of how you made your measurements. 

 

Jon



#6 GGK

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Posted 03 July 2022 - 08:40 AM

Gary:

 

I read your post carefully but I could not see an explanation of how you made your measurements. 

 

Jon

Sorry about that. 
 

Leveled TV-85 targeting a 1/32” graduated scale about 50 feet away. Two rounds of readings for each set-up. Calculated then averaged the magnification for the 4 combinations for each comparison.  Widest range within any average was 0.04X. I grouped the 6 and 8 Ethos values and also the 10 and 13 Ethos values due to same expected focal plane location. 

 

I questioned the initial measurements because the 10 Ethos with the 2.5X Luminous Barlow varied so much from the 8 Ethos. Then I looked up the focal plane location on the TV website. 
 

Gary


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#7 GGK

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Posted 03 July 2022 - 08:44 AM

I didn’t report the values because I didn’t repeat the measurements for verification, but putting the 8 Ethos in the tube extension of the BARCON without the lens cell, then inserting that into the Luminos 2.5X Barlow increased the magnification to over 3X. Makes for a long assembly, though.  
 

Gary


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#8 Echolight

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Posted 04 July 2022 - 12:20 PM

So if I space the Baader zoom out of the Luminos 2.5x barlow a bit it will increase the magnification?

 

I'm trying to get a little more than the estimated 156x magnification that I get in my ST102 without buying another eyepiece. Surprisingly, the CA wasn't killing me or the view of Saturn at 156x, so I figured why not go a little higher. Something closer to a .5mm exit pupil.

 

I found this thing here in my parts box. Guess I'll give it a try. 
7F7834F4-1F0B-4B1E-BE16-2E0EC436E9BB.jpeg


Edited by Echolight, 04 July 2022 - 01:06 PM.


#9 GGK

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Posted 04 July 2022 - 02:27 PM

So if I space the Baader zoom out of the Luminos 2.5x barlow a bit it will increase the magnification?

 

I'm trying to get a little more than the estimated 156x magnification that I get in my ST102 without buying another eyepiece. Surprisingly, the CA wasn't killing me or the view of Saturn at 156x, so I figured why not go a little higher. Something closer to a .5mm exit pupil.

 

I found this thing here in my parts box. Guess I'll give it a try. 
attachicon.gif7F7834F4-1F0B-4B1E-BE16-2E0EC436E9BB.jpeg

Looks like you found a 2” extension with M48 threads? Either that, or it has SCT threads and is the nosepiece to your Baader 2” diagonal. 

 

Yes, magnification is dependent on the optical length between the Luminous Barlow lens and the focal plane of the eyepiece, so it is a Barlow and not like a Powermate. More distance = higher magnification. Changing the spacing also changes the focuser position. 

 

Your trial will be interesting.
 

Gary


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#10 Echolight

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Posted 04 July 2022 - 02:38 PM

Looks like you found a 2” extension with M48 threads? Either that, or it has SCT threads and is the nosepiece to your Baader 2” diagonal. 

 

Yes, magnification is dependent on the optical length between the Luminous Barlow lens and the focal plane of the eyepiece, so it is a Barlow and not like a Powermate. More distance = higher magnification. Changing the spacing also changes the focuser position. 

 

Your trial will be interesting.
 

Gary

I'm not sure what it is exactly. But it threaded into the bottom of the eyepiece. And is long enough to where I can slide it out of the barlow a ways and still have something for the clamp to grip on. So I think it'll work for some experimenting.

97655F00-1036-4642-AFE0-06BB41A32767.jpeg



#11 Jon Isaacs

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Posted 04 July 2022 - 04:01 PM

Gary et. al.

 

Two questions:

 

- How long is the barrel?

 

-  How much inward or outward focuser travel is required?

 

Jon



#12 Echolight

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Posted 04 July 2022 - 10:13 PM

I figured out what my "extension tube" was. Goes on the end of the drawtube inside a Moonlight SCT focuser when it doesn't have a reducer attached inside..... I think.

 

So I figured I'd see if I could notice the increase in magnification. Don't tell anyone, but I turned the ST102 on the Moon and maxed it out.

I don't know exactly what magnification I was getting with the Baader zoom spaced out in the Luminos barlow.
It was a definite increase. The surprisingly sharp image showed some increase in size and details became easier to see. And at full zoom I began to see some floaters. So must have been nearing .5mm exit pupil. So possibly nearing 200x... maybe.

Still amazed that the f4.9 achromat could show so much details on the Moon. Very sharp really. Sometimes the right tool is the one your looking through.

 

I had it pulled out quite a ways. Guessing close to 30mm from normal.

32297615-CADB-4198-A01F-48C93096C0AE.jpeg


Edited by Echolight, 04 July 2022 - 10:19 PM.


#13 GGK

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Posted 05 July 2022 - 03:43 PM

Gary et. al.

Two questions:

- How long is the barrel?

- How much inward or outward focuser travel is required?

Jon

Jon,

I took some measurements while out this morning:

All dimensions should be within a millimeter.

Barrel length on the Luminos Barlow is 32.3mm. Overall length is 80.5mm, and the optical path length calculates to be about 6.6mm.

1. When using the 8mm Ethos with the 30mm TV barrel extender attached in my TV-85, the focus is 40.3mm out from Zero. I used this as a baseline.

2. When adding the Luminous Barlow to the 8mm Ethos / TV barrel extender, focus position moves 6mm inward.

3. When adding the Luminous Barlow plus a 31mm extension ring to the end of the 8mm Ethos / TV barrel extender, focus position moves 11.5mm inward from the baseline position in #1 above.

4. When adding the Luminous Barlow plus a 60mm extension ring to the end of the 8mm Ethos / TV barrel extender, focus position moves 14.9mm inward from the baseline position in #1 above. There might be an additional 1mm error here because power was too high, and I was having difficulty knowing where exact focus was.

I did not drift time #3 or #4 above, so don't I know the new magnification values with the extension rings. I just put the extension rings on to see the impact on focuser travel as the eyepiece moved further away from the Barlow lens.

I was using a diagonal with a TSFlat2 in place of the nosepiece, so didn't try the Barlow before the diagonal. I might do that with a standard diagonal next time just to see what happens.

The Barlow without the 2 to 1-1/4 adapter weighs 211g.

Gary
<edit for spelling error only>

Edited by GGK, 05 July 2022 - 08:43 PM.


#14 Jon Isaacs

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Posted 05 July 2022 - 05:40 PM

:goodjob:

 

Gary:

 

Thank you so much for taking the time to make the measurements for me. The short barrel of the 2.5:x Luminos caught my eye and it seemed like it might be a good fit for me with the 13 mm, 10 mm and 8 mm Ethos in both refractors as well as my Dobs with the Paracorr 2.

 

Currently I'm using the GSO Barlow and it works with the Dobs but not the refractors. 

 

I'll make some measurements of my own but it seems very promising.

 

Jon


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