5x Barlow 1.25 lens confusion

[Hiddenpalm]

So apparently knowing that you want a 5x 1.25 Barlow lens isn't enough. Can anyone constructively explain to an inexperienced amateur what is the difference between a $16 5x 1.25 Barlow lens and a $150 5x 1.25 Barlow lens, so I know what to look for when shopping for a 5x Barlow lens for my Nexstar 8SE?
 

$15 SVBONY Barlow Lens 5x 1.25" Fully Metal Multi Coated Optical Glass with T adapter M42 0.75 Thread for 1.25" 31.7mm Telescopes Eyepiece

$150 Orion 8715 High-Power 1.25-Inch 5x 4-Element Barlow Lens

 

Edited June 25, 2018 by Hiddenpalm

[IanC11]

Basically it's the quality of the glass used and build quality.

[Ricochet]

Is this for planetary photography? You will not need a 5x barlow for visual use with an 8se. 

Given the design of the Orion and the specification of it being 4 element I think it is fairly safe to assume it is a JOC (Explore Scientific) focal extender rather than a standard barlow. 

[Cornelius Varley]

I would even question the need for a 5x barlow for planetary imaging. The 8se has a focal ratio of f10 which with the barlow would take this to f50, which is far too high for the 8se. 

[JamesF]

I'd also agree that 5x is likely to be far too high for visual use.

For planetary imaging, camera pixel size really determines what barlow magnification you'd need.  A general rule of thumb is that you should aim for an f-ratio of somewhere around five to six times the camera pixel size in um.  Beyond that you're unlikely to get any better resolution, just a larger image (which you might as well do in post-processing if you want it).

For a camera with 3.75um pixels you'd therefore be looking at an f-ratio of around f/20 which you can achieve with a 2x barlow, or 2.5x at the most.

James

[Hiddenpalm]

Thanks for all the insight. The astrophotography isnt really that deep for me. Im just going to be messing around with a 12mp smartphone with FV-5 mounted on an adapter. Im more interested in stargazing while Im camping right now. According to the FOV Calculator there is a visual difference between the 2x and the 5x Barlow lens. According to those pictures, that's a pretty significant significance if your checking out some planets. Im aware that it won't be that clear.

But that's not really what Im trying to figure out. I just want to know, is there a noticeable visual difference between the $16 5x Barlow and the $150 5x Barlow? Im sure one is better made with better quality material. But what does that really mean?

Edited June 25, 2018 by Hiddenpalm

[cjdawson]

The difference in price will be the quality of the item.   The just take a look at the two pictures on amazon.  The cheap one, looks like it's made from a cheap piece of aluminium that's been powder coated, and has the lens attached - cheap to make.  I couldn't really tell you much about the quality of the lens(es) from the picture.  My initial guess is that it's a single element.

The orion one on the other hand looks to have been machined with a polished finished - so there's some attention to detail on the housing.   They say that it's a 4 element lens, so that's 4 seperate lenses stacked together to produce the final image.  I'd bet that the glass is higher quality to start with, then 4x the amount of glass.  Add coatings, and I'd hazard a guess that it'll have a better output than the cheap lens.

That said, I'd still want to do a side by side test to be sure.

[Ricochet]

14 minutes ago, Hiddenpalm said:

But that's not really what Im trying to figure out. I just want to know, is there a noticeable visual difference between the $16 5x Barlow and the $150 5x Barlow? Im sure one is better made with better quality material. But what does that really mean?

The more expensive item will be better corrected, and should have better lens coatings and hopefully fewer reflections from internal surfaces. Overall this will mean that the more expensive item should degrade the image less than the cheaper one. However, the difference in view is never as much as the price difference. Marginal gains become increasingly expensive to achieve and you have to decide through experience how much you are willing to spend. Many people will probably be completely happy with the SVBony, but some people would not even be happy with the Orion and would only use a Televue Powermate.

However, for visual use in your particular scope it is not necessary to buy ANY barlow at all. At f/10 you can just buy eyepieces. The eyepiece providing the optimum exit pupil for planetary observation is going to be in the 8-10mm range, but specifically for Jupiter even this could be too much. You probably want something that is going to give a magnification in the 150-200x range, so a 10-13mm eyepiece. I'm assuming that you used a 6mm Plossl in your FOV simulations because you already have one. This eyepiece is already small enough for diffraction to be scrubbing detail and you probably want less magnification instead of more. It is also worth remembering that a field of view simulator is exactly that. It does not attempt to simulate the effects on the image that excess magnification will have. I have edited the above simulations to better give you an idea of the blurring and dimming that excessive magnification will bring.

[Cornelius Varley]

The two images give the apparent difference is size between the 2x and 5x barlows.  The Celestron 8se has a practical maximum magnification of about 400x under perfect conditions.  In both of the cases the magnification shown is higher than that,. There is no benefit in trying to exceed the limits of the telescope.

The specification of the cheaper 5x barlow is a little vague. All we can determine from the listing is that it has multi coatings, a t-thread and apparently apochromatic. No mention of the number of glass elements in the design. It might not even be a 5x barlow. One of the reviews suggested that the magnification might be about 1.6x.

Would the Orion 5x barlow be better than the cheaper one ? Absolutely. Will you get any benefit out of using a high powered barlow ? Probably not. 

[newbie alert]

A fov calculator isn't going to show the atmosheric distortion

F50,and at 10000mm fl?..its not going to work..on my 8sct and the altitude of Jupiter at my location a x2 Barlow maybe in fantastic seeing conditions..x3 is too much..

[JOC]

Celestron themselves state a maximum useful magnification on this page https://www.celestron.com/products/nexstar-8se-computerized-telescope they guess at around 480x and that will be under perfect conditions, no thermals, no gunge in the atmosphere, no light pollution.  It looks like an F10 scope, my F6 is also 8" it will make a bit of a difference, but I can't get a better view of jupiter at more than about 150x magnification, i.e. with about an 8mm in the EP,  if I move to 240x - with a really decent 5mm it actually struggles to make the view better if conditions aren't good.  Your computer generated images above suggest magnifications of x677 and x1693 - My scope is a different design to yours, and I am only a novice, but I think if you believe you will get the 'Hubble' type images of Jupiter suggested by your pictures above, with a x5 Barlow then I think you will be incredibly disappointed, no matter what you have paid for it.  I'd suggest viewing it at about 200x (10mm) on a good night and spending a long time at the EP for the best views.

FWIW I think SGL often quote a rough rule of thumb for maximum possible usable mag. under optimum conditions and that is 2x apperture.  Your apperture is 203mm, so that would make the max. usable mag, about 406x - which isn't far from Celestron's own estimate of 480x.   To get 480x with a 2032mm scope, would mean nothing more powerful than 4mm formed with or without a x5 Barlow, i.e a 4mm EP without a x5 Barlow or a 20mm and a x5 Barlow, but unless you live somewhere with exceptional viewing conditions, I reckon 480x is still around twice what might be usable, based on what I know I can see.

If you haven't already done so check out the first page of this thread and even if you don't read it, scroll down and look at the pictures at the bottom 

You might wish to rejig your expectations.

 

Edited June 25, 2018 by JOC

[Stub Mandrel]

I have a cheap x5 barlow.

It's useless, either because it's too strong or it's just crap. I don't know which.

I have a low-mid x2 Barlow (Celestron) and a mid-range x3 barlow element of unknown origin and they are both excellent.

[Hiddenpalm]

Thanks everyone! I love how when I asked for more detail in the information you all came through, even with example images, like a professor I never had. Im new here, and this thread shows how extremeley helpful this community is. My 8SE should be coming in the mail any day now. I won't waste my time with a 5x barlow, though I might check out the 3x and or test the cheap ones to get the learning experience. In the mean time there is plenty of information on this thread alone for someone at my level to review a few times over. Thanks.

Oh and dont pay any mind that I live in NYC. We may have the most diverse selection of food in the world and some of the coolest scientists ever, but we don't have the stars. So Ive been using "Dark Sky Map" for android to find the perfect place in my region. Its about a 3 hour ride to the West Catskills. Something Im willing to do about once a week, given clear skies.

Edited June 25, 2018 by Hiddenpalm

[wesdon1]

On 25/06/2018 at 18:09, Hiddenpalm said:

Thanks everyone! I love how when I asked for more detail in the information you all came through, even with example images, like a professor I never had. Im new here, and this thread shows how extremeley helpful this community is. My 8SE should be coming in the mail any day now. I won't waste my time with a 5x barlow, though I might check out the 3x and or test the cheap ones to get the learning experience. In the mean time there is plenty of information on this thread alone for someone at my level to review a few times over. Thanks.

Oh and dont pay any mind that I live in NYC. We may have the most diverse selection of food in the world and some of the coolest scientists ever, but we don't have the stars. So Ive been using "Dark Sky Map" for android to find the perfect place in my region. Its about a 3 hour ride to the West Catskills. Something Im willing to do about once a week, given clear skies.

I'm a newbie too sir. I have wanted to know the answer to your question myself for a few months now, so thank you for asking it n thank you to all the very helpful advice from other more experienced members. Newbies like us need all the help n info we can get so places like SGL are invaluable to us. I'm on my 3rd Telescope. It's a SkyWatcher 200p Skyliner. It's 200mm aperture, 1200mm Focal Length. I also have a SW 130/900, and a SW 114/500, all Newtonian Reflectors. I'm 8 months in to my new hobby and it's amazing! Clear Skies to you all!

[Waldemar]

In short the difference between a good (read expensive like the PowerMates) Barlow and a cheap one is that the good one will do it's job without noticing it and the bad one will only be in your way and irritate the hell out of you...

[Stub Mandrel]

I wouldn';t expect (from experience) a cheaop x5 barlow to be any good. There are 'mid price' x3 barlows that are worth using. My Revelation Astro ED Barlow (x3) is very nice. I have an x3 insert of 'unknown origin' that came from Astroboot and it performs very well for imaging.