SvBony SV137 2x Barlow

[Nightspore]

I was pretty impressed with the SvBony 3x Barlow, considering its competitive retail price. This made me wonder about the 2x version of the same bargain basement model. So, for a grand total of £19.99p I ordered one.

 

 

My first impression of the Barlow, after taking it out of the box, was that it felt like it could have come out of a Christmas cracker.  It’s not heavy, lighter (barely 55 grams) in fact than its GSO equivalent, which is mostly made of aluminium. The SvBony has a chromed-brass barrel. The housing is very shiny, both outside and inside, which is not ideal.

 

 

I’m now pretty convinced that this is constructed from a lightweight polymer rather than a form of alloy. It may even be ‘kryptonite’. I don’t know. It is very shiny though.

 

SvBony’s marketing department claim:

 

“Cemented doublet and FMC film enhanced light transmission and achromatism; Unique matting ink around the glass lens decrease the stray light” (sic)

 

So I’m guessing the element edges have been blacked. The barrel is conventionally baffled, the element has no provision for a filter thread. From my measurements this ‘shorty’ Barlow is 75mm tall with a standard 22mm brass barrel. The element stands 16mm tall in its housing with at least 20mm of clear aperture.

 

 

Like its taller 3x sibling, the element is coated, although not obviously. I’ve read erroneous reports that these Barlows are uncoated. This is patently untrue as even a cursory glance reveals a pale green hint of optical coating. It’s probably fairly basic notwithstanding claims of ‘fully multi coated’. Although it doesn’t appear detrimental or affect its efficacy in use.

 

 

It features a brass compression ring and a plain brass screw. The screw isn’t the smoothest I’ve used but it held a Celestron zoom pretty securely. I certainly didn’t have any anxieties about it working loose. Many short Barlows have very small, almost undersized fastening screws.

 

 

I don’t always trust heavier eyepieces with these. The screws GSO use are very capable and have even been superseded by a bigger ‘chunkier’ version in the past few years or so. The SvBony at least equals the GSO in this respect. 

 

 

I directly compared the  SV137 with a stock 2x GSO short Barlow that has only a slightly more expensive retail price. The GSO is basically a bog-standard two element Barlow. The comparison was on various double stars that could be viewed with my modified ST80 and a Celestron zoom giving magnifications between 33.3x and 100x. The seeing was below average. I honestly couldn’t see any discernible difference between the two Barlows. They both gave sharp, bright images without any excess false colour or aberrations that I could see (I expect a certain amount of natural CA with the ST80). The ‘Christmas cracker’ SvBony should be at least as good as the GSO on most targets. The element is fairly well constructed but the housing has its issues in my opinion. It isn’t internally blackened and is probably some type of plastic. Optically I could perceive no difference to the similarly priced GSO unit. However, the eventual longevity of a plastic housing would concern me. 

 

 

Edited May 2, 2021 by Nightspore

[Marmot]

Another useful review of reasonably priced kit.

I like the way that you comment, not only on the performance, but also on the general build type and quality.

[Nightspore]

1 minute ago, Marmot said:

Another useful review of reasonably priced kit.

I like the way that you comment, not only on the performance, but also on the general build type and quality.

 

Thanks. I've always maintained that ergonomics and build quality can be as important as performance. Admittedly, overall aesthetics aren't so important, but if the set screw won't hold an eyepiece securely it could be a potential problem.

[Nightspore]

 

I’m still finding the Tele Vue 2x Barlow, 19mmTV Panoptic & 6mm Vixen SLV ‘minimalist’ collection surprisingly versatile with the Altair 60 EDF. It is the lightest and smallest grab and go set-up I have. The Panoptic gives about 19x and about 38x with the Barlow (roughly 3mm & 1.5mm exit pupils respectively). So I’m pretty much covered for rich field and medium deep sky magnifications. The Panoptic Barlows surprisingly well in the 2x TV, with no real vignetting or edge astigmatism, virtually right up to the field stop. The 6mm SLV gives 60x (1mm exit pupil) with 120x as the possible maximum. A couple of mornings ago I was observing Saturn. The conditions were not particularly good due to the humidity. When I switched to Jupiter it was a tad indistinct with definite atmospheric boiling at 120x. At 60x it wasn’t enough magnification to see any real detail. I wondered if the detached Barlow element from the TV 2x, when directly threaded into the SLV barrel, would give me a decent in-between magnification. Below: 6mm SLV & SV137 Barlow element.

 

 

This would be 90x or 96x depending how you calculate it, basically turning it into a 4mm (or thereabouts) eyepiece. I seriously doubted the TV element thread would be compatible with the Vixen. I was correct. I decided to wait until I’d packed-up and try another of my Barlow elements at a later date. Disappointingly, the otherwise excellent Orion Shorty 2x Barlow element thread was also incompatible with the SLV. Undaunted, I decided to try a few of my other short Barlow elements.
 

 

The Barsta-made Sky-Watcher 'Deluxe' element fitted fairly well, although I wasn't totally happy with some binding in certain spots in the thread. The GSO was a very smooth fit, as was the SvBony 2x element. I then performed a whole battery of daylight visual comparison tests with these elements. Then even more tests compared with a 4mm SLV eyepiece, GSO & Vixen 4mm Plossls, and finally 4mm Takahashi and Hutech orthoscopics. There honestly wasn’t much difference visually between any of them, except for FOV of course. The Takahashi ortho’ probably had the best overall contrast. I whittled it down to a choice between the SvBony and GSO elements to use with the 6mm SLV.

 

 

In this way I’d still really only be taking two eyepieces out with me. Both element housings appeared to be well made. I'm pretty certain they are both two element achromats. The GSO housing is slightly narrower and has a different focal plane to the SvBony. Probably as GSO 2x Barlows have 30mm barrels as opposed to the more common 22mm barrels used by SvBony and most other distributors. I can’t see any real difference between these elements when they are threaded into the 6mm SLV. However, I did think the SvBony had a smidgen more contrast, so it got the job. I tested it Sunday morning on a variety of doubles and inevitably on Jupiter.

 

 

I'm pretty impressed with the outcome and used it to view a Europa/Io conjunction.

 

 

The detached element fits snugly into this old GSO plastic container for transportation and is significantly lighter than carrying another eyepiece in my lightest grab & go bag. I also experimented with threading the SV137 element into the 19mm Panoptic. The thread fitted beautifully into the Panoptic barrel, which actually quite surprised me as TV threads aren't always particularly compatible. Daylight trials seemed promising with no real vignetting. Although, as I suspected, there was some serious lateral astigmatism in the outer field when I used the combination to view open clusters. It was perfectly fine on-axis. This is almost certainly because of the 68° AFOV of the Panoptic and not any fault with the SV137 element itself. I'm still impressed considering the entire Barlow was under twenty quid.

Edited June 27, 2022 by Nightspore

[Nightspore]

 

3x element gives around 1.4x in my estimate.

 

 

They have noticeably different coatings to the bog-standard GSO.

 

 

Considering what these Barlows cost they are excellent quality.