Explore Scientific 2x and 3x barlows? telextenders?

[Ags]

I have had a Revelation 2x barlow for a few years and have found this cheap and chearful unit has provided more superb service. I am thinking of an upgrade for imaging and visual fun. So I am looking at the Explore Scientific 2x and 3x units. I have heard they are good, but I am not sure what they are:

https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html

FLO confusingly titles them as "Barlow / Focal Extender", so which are they? I think they are telextenders, so they don't alter eye relief or eyepiece field of view. Am I right?

I am looking at getting the 2x unit first, which would give me finely graduated effective focal lengths of 3, 4.5, 6, 7.5 and 10mm, which would be perfect for my F5-F6 scopes. This would be from a mix of Vixen NPL, NLV and SLV eyepieces. The 3xis strictly on the 'maybe'list as it would be for occasional photographic use.

Edited October 23, 2023 by Ags

[Zermelo]

They are four-element telecentric multipliers, which have some advantages over telenegative Barlows. Televue Powermates have the same design.

https://www.cloudynights.com/topic/719810-a-4-element-barlow-is-it-even-necessary/

[Zermelo]

And here

 

[bosun21]

I have owned two of them and I found them very good. They are practically invisible when in use. I was considering buying a powermate but the ES is basically the same design with the same benefits.

[Ags]

Good to hear. All my 50-degree eyepieces are reasonable eye relief - the lowest is 15mm eye relief on my NPL 20, so the eyepieces would suffer from having eye relief extended by barlow. As for the NPL 20, I might replace it with an SLV 20 down the line, if one comes up second-hand at the right time. 

[Ags]

6 minutes ago, bosun21 said:

I have owned two of them and I found them very good. They are practically invisible when in use. I was considering buying a powermate but the ES is basically the same design with the same benefits.

Do the ES telextenders change the focus point much?

[John]

I've used the ES 2x focal extender and the 2.5x Powermate.

The ES unit does a pretty good job of emulating the Powermate's benefits. Perhaps a touch more light scatter and the ES did change the focus point a bit (can't recall how much but not a lot and it was inwards) whereas the Powermate is pretty much totally invisible and with little or no shift in the focus point. The ES was as sharp as the PM.

In other words the often encountered subtle difference in performance for a large additional outlay. 

 

Edited October 23, 2023 by John

[Mandy D]

1 hour ago, Ags said:

Do the ES telextenders change the focus point much?

In my experience with a 2 inch 2x one, they change it significantly for imaging. I had to add another 50 mm of extensions to my RC6 to achieve focus. On my 200P, I am able to pull it out 25 mm and rack the focuser out sufficiently to use it photographically, but it's not ideal.

[bosun21]

I have only used mine with my 102 refractor and the focus point was only moved about a half turn on the focuser.

[Louis D]

I have an ES 2x tele-extender that I picked up cheap and have yet to use it critically.  I've been preferentially using my Parks GS 2x shorty Barlow with my refractors lately.  If I get time, I'll have to have a shoot out with those two and my Meade 140 APO 2x, Tele Vue 2x, and Orion 2x Deluxe (all Barlows).  The last one doesn't work well with refractors being 6 inches long.

[Naughty Neal]

Svbony model sv216 is a 4 lens  barlow / focal extender, to all purposes it looks like an ES clone. 

I have seen it priced at £53 - £152, not much in the way of reviews even on CN.

SVBONY SV216 1.25" 2X 4-Element Barlow Lens for Imaging Visual Applications

Edited October 24, 2023 by Naughty Neal

[Zermelo]

I have 1.25"  x2 and x3 models from VisionKing and Opticstar (can't remember which way around) that I believe to be optically the same as the ES. One is quite a bit cheaper, new, than the ES; the other, not so. Second hand is possibly a bigger gap, as the ES probably hold their value more.

[bosun21]

There's no mention of the Svbony barlow being of a telecentric design. Neither in the description nor the specifications. 

[Don Pensack]

On 23/10/2023 at 13:40, bosun21 said:

I have owned two of them and I found them very good. They are practically invisible when in use. I was considering buying a powermate but the ES is basically the same design with the same benefits.

As long as the sky is quite dark.

The ES Focal Extenders have more light scatter than the TeleVue PowerMates.

If used for deep-sky objects and not planets and Moon, the ES and TeleVues are pretty interchangeable.

The PowerMates are arfocal with the eyepieces used without the PowerMates.  The ES require additional refocusing.  That may or may not matter.

[Mr Spock]

x2, x3 - why not split the difference  My x2.5 Powermate is excellent. Completely invisible in use and excellent build quality. 

[Louis D]

As far as cheaply priced tele-extenders, Astronomics is now marketing a 2x version under their Astro-Tech brand for $60 (plus sales tax).  I think it's getting decent reviews on CN.  Perhaps @FLO could bring it to the UK under one of their house brands?

[FLO]

On 23/10/2023 at 20:45, Ags said:

I have had a Revelation 2x barlow for a few years and have found this cheap and chearful unit has provided more superb service. I am thinking of an upgrade for imaging and visual fun. So I am looking at the Explore Scientific 2x and 3x units. I have heard they are good, but I am not sure what they are:

https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html

FLO confusingly titles them as "Barlow / Focal Extender", so which are they? I think they are telextenders, so they don't alter eye relief or eyepiece field of view. Am I right?

They are telecentric barlows. And, because they are telecentric, they are also known as Focal Extenders 🙂 

HTH, 

Steve

 

[FLO]

14 hours ago, Louis D said:

Perhaps @FLO could bring it to the UK under one of their house brands?

We have several new products arriving in November. I don't know if the barlow you mention is one of them. I'll post again if I find it is. 

Thanks for asking 🙂 

Steve 

[Don Pensack]

3 hours ago, FLO said:

They are telecentric barlows. And, because they are telecentric, they are also known as Focal Extenders 🙂 

HTH, 

Steve

 

The term "Focal Extender" was first used commercially, I believe, by Meade or Celestron back in the '70s.

It was a tube you added to the back of your SCT to extend backwards the focal point of the SCT, and it had camera T-Threads on the rear end so you could attach an SLR camera to the piece for prime focus imaging.

I think the purpose for the device was to lengthen the focal length of the scope and increase the image scale so the Moon and planets could be imaged.

Otherwise, I could see no reason not to make it quite short.

 

Meade later introduced a line of 4-element Barlows they termed "Focal Extenders" to differentiate them from others in the market.

They were made in China by Jing Hua Optical (JOC), and still are to this day, though they sell under other labels now, like Explore Scientific.

Technically, ALL Barlows are focal extenders.  That's what they do--extend the focal length.

And, nearly every one moves the focal plane out as well, though how this impacts the focal point of an eyepiece is determined by the focal length of the Barlow and the length of the upper barrel above the lens.

 

So the term "Focal Extender" does not necessarily mean the Barlow is telecentric.  Telenegative Barlows are focal extenders too.

[Louis D]

1 hour ago, Don Pensack said:

The term "Focal Extender" was first used commercially, I believe, by Meade or Celestron back in the '70s.

It was a tube you added to the back of your SCT to extend backwards the focal point of the SCT, and it had camera T-Threads on the rear end so you could attach an SLR camera to the piece for prime focus imaging.

I think the purpose for the device was to lengthen the focal length of the scope and increase the image scale so the Moon and planets could be imaged.

Otherwise, I could see no reason not to make it quite short.

 

Meade later introduced a line of 4-element Barlows they termed "Focal Extenders" to differentiate them from others in the market.

They were made in China by Jing Hua Optical (JOC), and still are to this day, though they sell under other labels now, like Explore Scientific.

Technically, ALL Barlows are focal extenders.  That's what they do--extend the focal length.

And, nearly every one moves the focal plane out as well, though how this impacts the focal point of an eyepiece is determined by the focal length of the Barlow and the length of the upper barrel above the lens.

 

So the term "Focal Extender" does not necessarily mean the Barlow is telecentric.  Telenegative Barlows are focal extenders too.

You must be a hoot at a party when something astro related comes up in small talk:  "No, that's not quite accurate.  You see, back when f/8 was considered a fast scope...." 😉😁

[Ags]

Sounds like my kind of party. You're both invited!

[Louis D]

6 hours ago, Ags said:

Sounds like my kind of party. You're both invited!

Me too.  Nothing wrong with such talk when everyone in the room is an astro geek.

[Don Pensack]

9 hours ago, Louis D said:

Me too.  Nothing wrong with such talk when everyone in the room is an astro geek.

Though it kind of makes the wives depart quickly from the room.

[Louis D]

4 hours ago, Don Pensack said:

Though it kind of makes the wives depart quickly from the room.

Sounds good to me! 😄

[Reeny]

On 23/10/2023 at 21:45, Ags said:

Good to hear. All my 50-degree eyepieces are reasonable eye relief - the lowest is 15mm eye relief on my NPL 20, so the eyepieces would suffer from having eye relief extended by barlow.

I am in the early stages of using the 1.25-inch VisionKing ES clone 2x barlow (4-element)

The results for your set-up will be slightly different, but I expect you will be pleasantly surprised using 50-52 degree Plossl type eyepieces on the ES or equivalent versions of the 4-element Barlow. 

I tried the 12mm Revelation/GSO type Plossl with 2x Barlow in the Heritage150 dob and wow - this is the combination I will be using the most from now on due to the unexpected wide angle view, and pin sharp image at 125x magnification.

Sharp focus with wider angle 60-66-degree EP's was difficult due to edge distortion - probably due to the small secondary mirror . And the scope runs out of clarity at high magnification, so the 9mm barlowed Plossl worked OK, but was not ideal for the conditions during the initial test at 170x mag.

The wider view needs to be checked out properly once the clouds clear. I still don't quite believe it myself, but there was at least 58-degrees or more available from the Barlowed Plossl. Maybe it was an optical illusion due to extended eye relief.