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Would this barlow be a problem?

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#1 Kn73

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Posted 10 August 2018 - 11:52 AM

Hello. I have the celestron 15mm luminos (https://www.celestro...-15-mm-eyepiece) and want to hook it up to this Barlow:
https://www.celestro...-3x-barlow-lens

Would this cause any problems? Would the 82 degree field of view suffer? Is it ok to combine the two?

Telescope: 8SE, 2000mm schmidt-cassegrain

#2 Cometeer

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Posted 10 August 2018 - 12:06 PM

Hello. I have the celestron 15mm luminos (https://www.celestro...-15-mm-eyepiece) and want to hook it up to this Barlow:
https://www.celestro...-3x-barlow-lens

Would this cause any problems? Would the 82 degree field of view suffer? Is it ok to combine the two?

Telescope: 8SE, 2000mm schmidt-cassegrain

 

It will be fine to combine them. FOV will not suffer. You might even gain ER.


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#3 oldtimer

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Posted 10 August 2018 - 12:11 PM

The FOV spec of the eyepiece would  not change BUT the true FOV would certainly be much smaller do to the increased magnification. Also it would be a rare night 400X would work well on anything but the moon.


Edited by oldtimer, 10 August 2018 - 12:14 PM.

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#4 sg6

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Posted 10 August 2018 - 01:03 PM

The combination will give just over 400x and it is doubtfu that the final image will be of much use, simply too much magnification. As a generalisation 200x is often cionsidered the maximum owing to the atmosphere. Some nights more will be possible but there will be more nights when 200x is too much rather then more then 200x being usable.

 

Why barlow an 8" SCT? Usually an SCT will produce more magnification the is readily usable. People more often end up adding in a reducer to bring it all down to around 1200 rather then upping the focal length to 6000+

 

With a 3x barlow your field of view will in effect reduce to a third of whatever it presently delivers. You have increased the effective focal length 3x so the mag is 3x more and that reduces your field by 1/3. Not sure how good the XCel LX barlow is also. Likely a decent barlow but you could need something better as in a TV powermate or ES tele-extender.

 

With an effective focal length of 6096mm the Luminos will give 406x and at 82 degrees that is 0.2 of a degree.



#5 mac57

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Posted 10 August 2018 - 01:16 PM

In my experience, very wide field ep's don't seem to Barlow as well as smaller field ep's.  The Luminos Barlow is pretty good, and I think the bottom cell unscrews.  3x seems a bit rash, as magnification can be a hindrance in poorer seeing conditions.  Your scope has a lot of built-in mag with its long focal length.Mark



#6 Rich V.

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Posted 10 August 2018 - 01:31 PM

Based on my experience with a C9.25, even a 2x barlow with a 15mm eyepiece will only be useful on nights with the very best seeing.  At a 5mm equivalent with a 3x barlow, you have a combo that will most likely only give "empty" magnification that will look grainy and reveal no more detail than a 10mm.  You will have a .5mm exit pupil which may be useful with a smaller refractor but usually not with your SCT.

 

I don't know where you're located so your general seeing conditions are unknown; I'd consider a 10mm eyepiece as a practical useful limit with perhaps occasional conditions that could allow a 7mm.  

 

Rich



#7 Poconut

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Posted 10 August 2018 - 01:59 PM

I typically view planetary with my 8" SCT at around 150x but can generally bump it up to 200-230x without problems on most nights.  I get a few nights when I can push it to around 310x, but that is usually about it.  Winter time, unfortunately, is better for that around here.



#8 Sky Muse

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Posted 10 August 2018 - 02:05 PM

There is one thing you might want to know: eclecticism.  In other words, Celestron eyepieces and accessories(barlows, filters, et al) do not perform some special type of magic when used in conjunction with your Celestron telescope, nor are they any more compatible with your telescope, and when compared to same of other brandings.  Now, if you like matching "dishes and tableware", go for it, but you could be missing out on better performance by not expanding your horizons.  However, if you ever do consider a focal-reducer, as mentioned, do get the Celestron.  But with everything else, try this brand, that brand, and any other brand of this and that.

 

For a 2032mm focal-length, if you really feel the need for a barlow, get a 2x.



#9 Kn73

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Posted 10 August 2018 - 04:49 PM

I will get a 2x barlow then.

I cannot get the luminos barlow because the bottom of that is 2“. I still have the normal 1 1/4“ on my telescope and that is not compatible. Very unfortunate

#10 Kn73

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Posted 10 August 2018 - 04:51 PM

Sky Muse I decided between the celestron Luminos and a non-celestron eyepiece. But because of the 80+ fov I chose the celestron

#11 Poconut

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Posted 10 August 2018 - 05:19 PM

I will get a 2x barlow then.

I cannot get the luminos barlow because the bottom of that is 2“. I still have the normal 1 1/4“ on my telescope and that is not compatible. Very unfortunate

An easy way to fix that is:

 

https://agenaastro.c...BSABEgJoqPD_BwE



#12 Sky Muse

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Posted 10 August 2018 - 07:11 PM

I will get a 2x barlow then.

I cannot get the luminos barlow because the bottom of that is 2“. I still have the normal 1 1/4“ on my telescope and that is not compatible. Very unfortunate

Why would you want to barlow 2" eyepieces?  You'd have to get that 2" visual-back, as suggested previously...and a 2" diagonal, unless you observe straight-through; although there are quite a few users who do that very thing.

 

Barlows are for reaching a higher power where it would be difficult to use only an eyepiece at that power, like when 3x-barlowing a 9mm for a simulated 3mm.  They also help to save when buying eyepieces.  With a barlow and three carefully-chosen eyepieces, you then have six powers from which to choose, instead of having to purchase six eyepieces; four items instead of six.  You don't want to duplicate the powers within the set, so the eyepieces, again, should be chosen carefully.  Then, you perhaps want to retain as wide a field-of-view as possible when observing at a high power, for the extra "real estate" seen surrounding an object of interest, and by barlowing a longer wide-field eyepiece.  By 2x-barlowing the 15mm, you will get a simulated 7.5mm(271x).  Simply ensure that the collimation of the Schmidt is spot-on, and hope for nights of good seeing.  They'll come along for you, and make it worth all the while...

 

http://www.scopestuff.com/ss_ebt2.htm

 

You do not really need a 2" barlow, in any event, but they're your purse-strings.  I rarely, if ever, barlow an eyepiece longer than 12mm, and with telescopes of less than 1000mm of focal-length, therefore I have a need for barlows, 2x and 3x.  But I use just the eyepieces, without a barlow, for the low-to-medium powers.



#13 Poconut

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Posted 10 August 2018 - 07:24 PM

No problem with a 2" visual back on the 8" SCT.  If you ever acquire accessories in the future with 2" requirements (camera, diagonal, barlow, eyepieces, etc...) you will be all set.  My camera requires 2".  My Baader eyepieces can take either 2" or 1.25", so 2" fits the bill for them (I use them the most anyhow).  I have at least three 2" to 1.25" adaptors at my disposal and not sure where they even came from, so using your 1.25" should never be an issue.

Sure it sets you back in $$, but I think it is a good upgrade.  A 6" SCT, not-so-much.


Edited by Poconut, 10 August 2018 - 07:26 PM.


#14 Kn73

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Posted 11 August 2018 - 05:28 AM

I do not want a 2“ barlow. I thought that the barlow had 1.25“ compatibility on both sides but it only allows 1.25“ on one. My entire setup is still 1.25“ so I cannot use that barlow.

Completely upgrading to 2“ or getting the linked adapter ontop for 100$ now is a too pricy for me atm, since I‘ve just bought accessories. I will buy the Barlow that I linked in the OP

#15 gnowellsct

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Posted 12 August 2018 - 02:57 PM

An easy way to fix that is:

 

https://agenaastro.c...BSABEgJoqPD_BwE

That's a nice gadget but likely not what he needs.  He needs a simple 1.25 inch to 2 inch adapter; once he has one, he can use it with the Baader or anything else....IF he has a 2 inch diagonal.  Which I don't think he does.  Greg N  



#16 gnowellsct

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Posted 12 August 2018 - 03:01 PM

OP might be better off with 10mm and 7 mm eyepieces.  10 mm is 1 mm exit pupil and "perfect" for the f/10 SCT and the 7mm boosts magnification that is more likely to be useful  (285x).  

 

I have quite a few barlows but never use them, which is a thing that happens when one's dedicated eyepiece collection fills out.  But as it turns out my remaining use for a barlow is in my daystar quark configuration for h-alpha solar viewing.  The "regular barlow" in the link would not work for that application.  

 

Greg N


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#17 spaceoddity

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Posted 13 August 2018 - 04:45 PM

https://agenaastro.c...arlow-lens.html



#18 Poconut

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Posted 13 August 2018 - 06:44 PM

That's a nice gadget but likely not what he needs.  He needs a simple 1.25 inch to 2 inch adapter; once he has one, he can use it with the Baader or anything else....IF he has a 2 inch diagonal.  Which I don't think he does.  Greg N  

Why would he need an adaptor if he doesn't have 2" plumbing to begin with??  I was suggesting a 2" visual back for his SCT.  He has an 8SE which has a 1-1/4" visual back.


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#19 jallbery

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Posted 13 August 2018 - 07:49 PM

On an 8SE, I'd stick to 1.25" accessories and use the Celestron Reducer/Corrector to achieve wider fields when desired.   Everything a 2" diagonal and 2" eyepieces can show you on a C8, can also be seen using the R/C and 1.25" eyepieces at reduced $$$ and reduced weight.

 

As far as a barlow to use with the 15mm Luminos,  if that were my goal, I'd look at the GSO 2X with the nose piece that can be removed and attached directly to an eyepiece for a roughly 1.5X magnification.  That would give you the option of both an approximate virtual 10mm and an approximate virtual 7.5mm.



#20 Poconut

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Posted 13 August 2018 - 08:27 PM

On an 8SE, I'd stick to 1.25" accessories and use the Celestron Reducer/Corrector to achieve wider fields when desired.   Everything a 2" diagonal and 2" eyepieces can show you on a C8, can also be seen using the R/C and 1.25" eyepieces at reduced $$$ and reduced weight.

 

As far as a barlow to use with the 15mm Luminos,  if that were my goal, I'd look at the GSO 2X with the nose piece that can be removed and attached directly to an eyepiece for a roughly 1.5X magnification.  That would give you the option of both an approximate virtual 10mm and an approximate virtual 7.5mm.

A 2" visual back gives you flexibility to use 2" accessories and also your 1-1/4" eyepieces (with adaptor).  The f/6.3 focal reducer, which I also have for my 8SE  is fine and all, but you are still limited to 1-1/4".  Besides the $100 to upgrade the 8SE to 2" plumbing, there is little reason not to do it by default.

The F/6.3 reducer still limits you to 1-1/4" viewing.  In my case this does not work with my QHY APS-C sensor camera, but it does work with my DSLR using the Baader eyepieces afocally .. different application.  I could get a 'special' camera for 1-1/4", but why?  Cameras are much more expensive than converting to 2" plumbing at the source.  It's more fun, and another excuse to get another scope designed for wide angle viewing !!


Edited by Poconut, 13 August 2018 - 08:42 PM.


#21 gnowellsct

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Posted 13 August 2018 - 09:16 PM

Why would he need an adaptor if he doesn't have 2" plumbing to begin with??  I was suggesting a 2" visual back for his SCT.  He has an 8SE which has a 1-1/4" visual back.

I'm not sure you were clear in communicating all that.  Or maybe I was not clear in reading it.  GN



#22 jallbery

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Posted 13 August 2018 - 10:27 PM

A 2" visual back gives you flexibility to use 2" accessories and also your 1-1/4" eyepieces (with adaptor).  The f/6.3 focal reducer, which I also have for my 8SE  is fine and all, but you are still limited to 1-1/4".  Besides the $100 to upgrade the 8SE to 2" plumbing, there is little reason not to do it by default.

The F/6.3 reducer still limits you to 1-1/4" viewing.  In my case this does not work with my QHY APS-C sensor camera, but it does work with my DSLR using the Baader eyepieces afocally .. different application.  I could get a 'special' camera for 1-1/4", but why?  Cameras are much more expensive than converting to 2" plumbing at the source.  It's more fun, and another excuse to get another scope designed for wide angle viewing !!

I was only speaking of visual use.  If you are getting into EAA or astrophotography, you buy whatever hardware necessary to connect your camera to your scope.  To use a DSLR with the R/C (assuming it has an APS-C-sized sensor), I'd buy the SCT T-adapter and the requisite T-ring and skip eyepiece-sized adapters.  It will give you the correct spacing and a solid mechanical connection.

 

From a visual perspective, using the R/C doesn't limit you to 1.25" -- it effectively eliminates the need 2" accessories for a C8, which can save you a ton of cash: your longest 1.25" eyepieces get to perform double duty, you avoid the expense of 2" eyepieces, and you get to stick with 1.25" filters.

 

The cost of the R/C vs a decent 2" SCT diagonal is a wash.   The R/C turns a 1.25" 32mm plossl into a virtual 55-56mm 2" plossl.   It turns a 24mm 68 into a virtual 40mm.  

 

A 24mm ES 68 costs $139 and weighs under 12 oz.

 

A 40mm ES 68 costs $309 and weighs more than 31 oz.

 

True field of view with the 24mm 68 and the R/C on a C8:

27.2*57.3 / 1280 = 1.22 degrees at 53.3X

 

Field of view with the 40mm 68 and a typical 2" SCT diagonal :

45.5*57.3 / 2100 = 1.24 degrees at 52.5X

 

So you save about $170, and over a pound in weight, AND get to use the 24mm ES68 without the reducer, too (yielding a nice 0.77 degrees at 84.7X).

 

And it will turn the 15mm Luminos the OP has into a virtual 23-24mm 82-degree AFOV eyepiece.


Edited by jallbery, 13 August 2018 - 10:32 PM.



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