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Deciding on a Barlow, is my train of thought here right?

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#1 iRunBadC93

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Posted 22 June 2021 - 12:55 PM

I want to make sure I'm on the right track here. Newbie trying to put together some EPs for the AD8 my brother and I are getting delivered tomorrow. After reading through several topics, we've decided to go the route of getting a SVBONY 7-21 zoom (already received) and a Barlow, in addition with the 9mm plossl and the 30mm 68 degree super view that come with the scope. Being that we are complete amateurs , I'm trying to take the advice of not going overboard on EPs to begin. Hence the decision on the zoom, aware of the trade offs in tfov and all. Seems like a decent place to start. But I don't want to cheap out where we should not. So I'm wondering if we should be considering going with a higher quality barlow now, or if that is inefficient.. 

First of all, we have a 2" focuser on the AD8. Originally I thought that meant we should most certainly be getting a 2" barlow. But I did read an article Ed Anderson has linked in many other threads on choosing a barlow, and am beginning to think that we should be going for a 1.25. Reason being that if we can get one that has a removable element, we can magnify every focal length of the SVBony zoom at 1.5x and 2x, right? Because with a 2" barlow the removable element is at 2" dia? 

 

And second, https://telescopicwa...ens-and-how-to/ this was the link listed. Now the GSO shorty 1.5x/2x is the only Barlow listed here that has the removable element if I understand correctly. Anyone have experience with it, and/or a mid-higher range option? If we find ourselves in the future with a ton of higher quality single fl EPs, will a Barlow as cheap as this GSO shorty hinder the quality of our EPs? Because if so then I don't see a reason to grab an entry level piece , ya know?

Thanks guys!
 



#2 havasman

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Posted 22 June 2021 - 01:46 PM

Hi iRunBadC93 and welcome to the forums,

 

Congratulations on the new scope. That's a powerful instrument that will keep you busy for years. Barlows are specialized tools that are packed in "beginner" eyepiece kits from the mass market suppliers to get the piece count up so they'll seem like greater bargains. [They're not and you did well to avoid them.] So most beginners think they need one and also overestimate the usefulness of very high magnification observing when starting out. You have a wide range of focal lengths covered with the eyepieces you have and will receive with the scope package. It's extremely unlikely a Barlow will enable you to see anything more than your native focal length eyepiece kit will. I advise you to use what you'll have to learn what works best for you at your site for observing the objects you will come to most enjoy. You may be best served by upgrading whatever focal length you particularly come to find useful (likely in the 8 to 16mm range) well before needing higher magnification. Then if later you decide you need a Barlow, there will still be plenty from which to choose.

 

The best accessory for ANY scope is more time spent carefully observing from the best site you can access.


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#3 f74265a

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Posted 22 June 2021 - 02:04 PM

Agree with above about waiting on barlow.
The zoom should get you to approx 170x. It will depend on your local seeing conditions as to where your useful magnification will usually top out. Granted I have smaller aperture, but I will say that I use 170x or less 99% of the time. My seeing here rarely allows more. If you find out that 170x works great frequently, then add a barlow or a decent 6mm eyepiece
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#4 iRunBadC93

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Posted 22 June 2021 - 07:49 PM

Agree with above about waiting on barlow.
The zoom should get you to approx 170x. It will depend on your local seeing conditions as to where your useful magnification will usually top out. Granted I have smaller aperture, but I will say that I use 170x or less 99% of the time. My seeing here rarely allows more. If you find out that 170x works great frequently, then add a barlow or a decent 6mm eyepiece

Thanks. Yes, so I'm understanding that the vast majority of the viewing we'll be doing in the Columbus area will definitely not be requiring higher mags than 170x haha. We'll be doing the majority of our viewing in the near future at hocking hills. But I do like the idea of being able to have the ability to have a mag range above that, given in some way we get amazing seeing conditions. We visit Marinette , WI multiple times a year and have access to some pretty dark skies near the UP, and will be visiting over the week of the 4th of July. Also plan on a couple trips to Cherry Springs this year ! 

I guess I'm also looking for some confirmation in my thought process regarding the size and quality of a Barlow and how it affects future EPs. 



#5 Frugal Astronomer

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Posted 22 June 2021 - 08:03 PM

I have the AD8, the SvBony 7-21 zoom and a GSO APO 2.5x barlow (among other eyepieces).  I personally haven't found that zoom all that useful due to its limited AFOV.  I've used it a few times on double stars, but that's about it.  With a manual scope, things drift out of view fairly quickly, so I've learned that I prefer a minimum of 60* AFOV.  I've found the Starguider/Paradigm Dual ED eyepieces to be a very good value and very comfortable to use.  I started out with the 25mm, 18mm, and 12mm with the GSO (1.25") barlow to give me higher mags with each.  I now have the 25, 15 and 5 with a 20mm ES and a 11mm ES hitting some "sweet spots" for me.


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#6 f74265a

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Posted 22 June 2021 - 08:03 PM

If you are going to get a barlow, I would get definitely a 1.25 rather than a 2 inch. Less cost, less weight. And your zoom is 1.25. Moreover, most 2 inch eyepieces are longer focal length and, generally speaking, don’t barlow as well (they vignette, have eye relief extended too far). As for which one, I’ll let others suggest a quality lower priced option as my interest and knowledge focuses on the high end products
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#7 sevenofnine

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Posted 23 June 2021 - 07:03 PM

The focal ratio of the AD8 is about f/6. There's a general rule that the highest power eyepiece is equal to the focal ratio of the scope under average to good seeing conditions. There are exceptions but this means that your highest power eyepiece is going to be a 6mm. No matter how you get there. For example a straight 6mm eyepiece or a 12mm with a 2x barlow. So a barlow may help you fill in gaps in your eyepiece collection but trying to get super high magnifications usually means a larger but very soft image with little or no detail. I would pass on the barlow for now. Good luck! waytogo.gif



#8 f74265a

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Posted 23 June 2021 - 09:49 PM

Consistent with this last post, I above suggested the idea of a decent 6mm if you really find 171x insufficient. 6mm would be 200x- more than enough for most things and, at least where I live, not usable on many nights.

#9 vtornado

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Posted 24 June 2021 - 05:00 PM

Thanks. Yes, so I'm understanding that the vast majority of the viewing we'll be doing in the Columbus area will definitely not be requiring higher mags than 170x haha. 

 

Actually in Columbus you might want to exceed 170.

 

High magnification and high magnification objects can withstand light pollution better then large diffuse objects.

Low power, big views are going to be ho-hum because of sky washout due to light pollution.

 

Now I'm not say go up to a gazillion, but good barlows are not much money ($30.00).  They may be useful

for lunar, planetary and double star observing.   With the moon I can sometimes go 300x.  Which for your

scope would a 4mm eyepiece (or 8mm on your zoom doubled with a barlow).

 

One of the great things are about barlows is that it keeps you from buying a short fixed dedicate eyepiece

that will see infrequent use.

 

I'm also not saying you have to rush out and get a barlow either.   Take your time use what you have and

if you are still hungry for more mag,  go get yourself a barlow.  As others have said mag is not free.

The image will get blurrier, dimmer and you will have to "bump" your scope more often to track.

You can save yourself a little dough by buying from the classified here.

 

I live in the same sort of air regime that you do.  (Upper midwest) Most nights are 150-180 for moon, fewer are

180 - 220 and fewer still  nights is 220 - 300.   Upper level winds here have been strong at night lately.  Lunar viewing

has been throttled to 150 no matter what scope I use.


Edited by vtornado, 24 June 2021 - 05:01 PM.



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