39 replies to this topic

[revans]

With longer focal length reflectors used for lunar/planetary work, it would be nice to have a 1.5x available so that you don't "magnify" more than the seeing will allow.  The only 1.5x barlow I've seen is a Masuyama and it is always out of stock.  There are 1.25" thread on 1.5x barlows designed for binoviewers really, that can be threaded on eyepieces or camera nosepieces but I don't know how well they would work outside of a binoviewer usage.  Takahashi makes a 1.5x tele-extender but I don't know if it would work on other scope types and it costs $650 which seems pretty pricey. Why is nothing else available?

 

Rick

[hyiger]

With longer focal length reflectors used for lunar/planetary work, it would be nice to have a 1.5x available so that you don't "magnify" more than the seeing will allow.  The only 1.5x barlow I've seen is a Masuyama and it is always out of stock.  There are 1.25" thread on 1.5x barlows designed for binoviewers really, that can be threaded on eyepieces or camera nosepieces but I don't know how well they would work outside of a binoviewer usage.  Takahashi makes a 1.5x tele-extender but I don't know if it would work on other scope types and it costs $650 which seems pretty pricey. Why is nothing else available?

 

Rick

For this reason I've found that my Baader 8-24mm zoom works well. I can adjust as seeing allows. 

[Mike Allen]

Vernonscope makes a 1.5x and 1.25x barlow that can screw on to standard 1.25” oculars.  They call it their Magic Dakin barlow.  I believe it costs $149.

[Astrojensen]

If you unscrew the lens cell from a normal 2x short Barlow, and thread it directly into the filter threads of a 1.25" eyepiece, it will work at approximately 1.5x. 

 

 

Clear skies!

Thomas, Denmark

[Mike Allen]

Siebert Optics make a 1.5 barlow.  Although I don’t own one, they seem to be highly regarded here on Cloudy Nights.

[revans]

If you unscrew the lens cell from a normal 2x short Barlow, and thread it directly into the filter threads of a 1.25" eyepiece, it will work at approximately 1.5x. 

 

 

Clear skies!

Thomas, Denmark

Brilliant !

 

Rick

[SkyHunter1]

Rick,

Go here: https://www.sieberto...cs-barlows.html

 

Great barlows in any configuration. I have 2 1.5x barlows from Siebert. You can call and hes awesome and will suggest the best barlow. i have this one: 1.25" Performance Telenegative/APO

 

he makes barlows that you can add the camera as you would an eyepiece and he has the screw on camera adapter too. you can specify what you want or need. i have the screw on head.

 

You can check out my astrobin for my planetary and lunar images if youre interested in the quality. ZWO uses my jupiter image on thier site if thats any indication of performance. You wont be dissapointed.

 

Regards,

Skyhunter1

Edited by SkyHunter1, 03 January 2025 - 12:37 PM.

[rsalva1]

I used to have this before switching out to the more expensive Tak version. Only reason I switched out due to imaging and I had a Tak. Otherwise, it was fine, good contrast and does not break the bank.
 

https://telescopesca...k-barlow-2ubstl

[Starman1]

Baader VIP Barlow: One of the finest Barlows made and yields magnifications of 1.76x, 2.0x, and 2.6x with the out-of-box parts, it is usable in 1.25" or 2" focusers (uses only 1.25" eyepieces, however),

and by changing adapters can yield other magnifications:

https://agenaastro.c...vip-barlow.html

See text for details.

Usable photographically or visually.

Edited by Starman1, 03 January 2025 - 01:04 PM.

[Jethro7]

Takahashi makes a 1.5x tele-extender but I don't know if it would work on other scope types and it costs $650 which seems pretty pricey. Why is nothing else available?

 

Rick

Hello Rick,

I use the Takahashi 1.5X Tele-Extender. Takahashi desined this focal extender to work with their highly corrected triplets. However, I use the 1.5X Tele-Extender with all of my Tak refractors from the 60mm, 76mm,120mm as well as my TEC140 and the big TS Optic 155. So I can faithley report that the 1.5 X Tele-Extender works nicely through any well corrected refractors. The Tak 1.5X Tele- Extender has become one of my favorite appliances and is invisible when used. With that being said, I've never attempted to see if it would work with my fast 152mm Achro because the nitche for that scope is a Richfield Refractor and would be pointless. As far as working with an SCT or Newt, I don't know but my suspicions are no. However this is interesting and I did a bit of a quick research in the CN, archives about this topic without any conclusion. I don't think anyone has bothered to try this out, or if they have, they have not posted any results. Maybe I need to try and see if it works. The reason that there is not much to choose from when it comes to 1.5 X Barlows is. My guess would be, most of the viewing public simply prefer a Barlow that offers more magnification. The alternative is What Thomas said.

 

HAPPY SKIES AND KEEP LOOKING UP Jethro

Edited by Jethro7, 03 January 2025 - 01:17 PM.

[RAKing]

The Baader VIP barlow is an excellent barlow, that can easily run from 1.5x to 2.5x.  The VIP has a focal length of 64mm, so you can vary the spacing between the field stop of your eyepiece and the barlow lens to get the barlow "boost" you need. 

 

I use it with my Leica zoom and if I attach the T2 barlow fitting directly to the bottom of the zoom's adapter, it's right at 32mm, so I get 1.5x magnification.

 

Cheers,

 

Ron

[TOMDEY]

A decade or few ago, there were quite a few Barlow nominal/inscribed amplifications to choose from. I have some of those kicking around here in tubs... 1.5x, 1.8x, 2.0x, 2.5x, 3x etc.) and in .965, 1.25, and 2-inch barrels. It's always perplexed me that they nowhere state the truly most fundamental 1st order tech spec... which is the (negative) focal length f or power D of the thing. Engraving its amplification is similar to engraving an eyepiece's magnification --- sort of meaningless, without knowing how and where you are going to use it. Must be (once again) that the manufacturers presume that their customers are kinda dense... and would just get confused --- which (alas) is a reasonable assumption.

 

Couple examples here. Three Barlows from my tubs. I (quickly and coarsely) measured the dioptric power of each and get these numbers >>>

 

Barlow                  engraved          optical power  focal length

                           amplification

 

Orion Tri-Mag           3x                      -18D             -56mm

Orion 2"                   2x                       -8D             -125mm

Tele Vue                  1.8x                     -7D             -143mm

 

Once you have that refractive power (which literally means Zernike Power, but expressed in diopters) or focal length... it's then easy to compute what amplification you will realize in each and every of your intended applications and spacing configurations. Couple pictures here, including my cartoon showing how to  more accurately measure the focal length of a negative lens.    Tom  

Attached Thumbnails

• 
• 
• 

Edited by TOMDEY, 03 January 2025 - 01:57 PM.

[Arnau_BCN]

Masuyama have a 1.5x barlow but I also  agree in the Baader VIP. Also this 1.8x from APM looks great too. https://www.teleskop...lens-1-25-16064

Edited by Arnau_BCN, 03 January 2025 - 02:18 PM.

[25585]

They are not so hard to find. Masuyama does a 1.5x, Nikon a 1.6x, and Antares a 1.6x.

Edited by 25585, 03 January 2025 - 02:56 PM.

[revans]

They are not so hard to find. Masuyama does a 1.5x, Nikon a 1.6x, and Antares a 1.6x.

The Antares 1.6x seems to be available only as a 2" rather than a 1.25" but I suppose it would accept a 2" to 1.25" adapter.  Sometimes though, using these adapters can introduce some tilt into an imaging system and care is needed introducing one.  I didn't notice this until I started to do star testing for collimation purposes using one.  I'd be mostly using the 1.5x or 1.6x on a camera nosepiece.  The Nikon 1.6x seems to be for eyepieces only and I'm not sure it can be used with a camera. The Masuyama 1.5x is seldom in stock.

 

Rick

[revans]

Brilliant !

 

Rick

I had a Celestron 2x short barlow in my eyepiece box.  I unscrewed lens containing lower portion of it and tried to thread it onto a regular 1.25" eyepiece and being unsuccessful, tried to thread it onto the nosepiece of an astrocamera... also unsuccessfully.  Maybe it is just the Celestron short barlow that is the issue.  At the moment it is the only 2x barlow I have, my other barlows being at 2.5x, 3x and 5x. 

 

Rick

[dmgriff]

 Antares 1.5x

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

 

Masuyama 1.5x

https://astrohutech....-barlow-lenses/

 

Siebert Optics manufactures several barlows/telecentrics 1.5x

https://www.sieberto...cs-barlows.html

[revans]

I just noticed that my Williams Optics binoviewer came with both a 1.5x and a 2.5x thread on barlow.  Either will fit onto a regular 1.25" eyepiece or an astrocam 1.25" nosepiece.  Maybe the 1.5x thread on barlow can be used in the same way as the Vernonscope Magic Dakin 1.5x barlow.  I will have to give that a try.

 

Rick

[Jon Isaacs]

My 2 cents:

 

As Tom said, once you know the focal length of a Barlow, you can compute the amplification factor based on the spacing between the Barlow's optics and the focal plane. 

 

A = 1 + D/F where D is the distance from the optics to the focal plane and F is the absolute value of the focal length. Negative lenses have negative focal lengths.

 

One can estimate the focal length by inspection. For a 2x Barlow, F= D. For a 3x Barlow, F= D/2.

 

I have found the following info on the web:

 

A-P Barcon -127 mm

TV 2x, 1.25 inch -74.4 mm
TV 3X, 1.25 inch -52.3 mm
TV 2x, 2 inch Big Barlow -90.4

 

I have the GSO 2 inch 2x ED Barlow. By drifting timing and respacing the Barlow, I've estimated that the focal length is approximately -100 mm. I use it spaced to provide 1.75x, it increases the back focus so it can be used with the Paracorr 2.

 

My friend Bruce (Astro-Master) has made a science of using the 17 mm and 13 mm Ethos with the 2x Big Barlow and the Barcon with spacers to provide a wide range of magnifications. He's gone as far as drift timing them to know the exact magnification.

 

As to why there aren't too many 1.5x Barlows, I think it's because a 2 x Barlow is more versatile. Say you have a 7 mm eyepiece and a 5 mm eyepiece. With a 2x Barlow, you get 3.5 mm and 2.5 mm. With a 1.5x Barlow you get 4.7 mm and 3.3 mm. 

 

Jon

[Andrea Salati]

I have developed a passion for buying cheap but optically good barlow lenses neglected by their owners and using them in my rigs for optimizing the sampling.
Currently I am using the doublet from an Orion Tri-Mag for an effective magnification of 1.41x on the solar rig and that of a very old, Vixen made, Orion 2x for an effective magnification of 1.53x on the gas giants rig.

For visual use I keep a Tele Vue 2x and I have had some fun adding the eyepiece holders of the two barlows mentioned above which work as extenders. One can have quite some fun, as Jon pointed out.

I am grateful for Tom's sharing the focal lengths of two of my three barlows, it is something I will save in my notebook.

Edited by Andrea Salati, 04 January 2025 - 08:01 PM.

[Sol Robbins]

Nikon Ei6 is 1.6x and ranks amongst the best Barlows I've used. It also achieves focus with my various telescopes.

[BFaucett]

I had a Celestron 2x short barlow in my eyepiece box.  I unscrewed lens containing lower portion of it and tried to thread it onto a regular 1.25" eyepiece and being unsuccessful, tried to thread it onto the nosepiece of an astrocamera... also unsuccessfully.  Maybe it is just the Celestron short barlow that is the issue.  At the moment it is the only 2x barlow I have, my other barlows being at 2.5x, 3x and 5x. 
 
Rick

 
These work for me.
 
GSO 1.25" 2x "Shorty" Achromatic Barlow Lens # GS2BL
"Barlow element can be separated from main tube and threaded directly into a 1.25" eyepiece for approximately 1.5x increase in magnification."
https://agenaastro.c...arlow-lens.html
 
GSO 1.25" 2x "Shorty" Achromatic Barlow Lens with T/T2 Thread # GS2BL-T2
"Barlow element can be separated from main tube and threaded directly into a 1.25" eyepiece for approximately 1.5x increase in magnification."
https://agenaastro.c...h-t-thread.html
 
 
Just trying to be helpful. Cheers! Bob F.  
 
 

 

[Andrea Salati]

I have found the following info on the web:

 

TV 2x, 1.25 inch -74.4 mm

My friend Bruce (Astro-Master) has made a science of using the 17 mm and 13 mm Ethos with the 2x Big Barlow and the Barcon with spacers to provide a wide range of magnifications. He's gone as far as drift timing them to know the exact magnification.

Jon, after you posted this, I did some measurements and I came up with -73.2mm for my TeleVue Barlow. I should repeat them and try to be more accurate. Mine seems to be more like a 2.1x than 2x

Anyhow, last night seeing was much better than it has been in recent times so I had some fun on Jupiter. I actually was able to deploy a 3.5mm XW which sees the focuser very seldom, almost never. Inspired by the conversations about barlow lenses and spacers, I decided to do something with the "empty" Orion barlow bodies in the case. They are empty because their optical groups are "permanently" housed in the optical trains of my two small imaging rigs.
Anyhow, having removed the lenses, they are extenders, one adding 60mm and the other one 86mm.
I had fun with the TeleVue Barlow plus these extenders plus a cheap and often ignored Orion Explorer II 17mm. With the 60mm extender, the equivalent focal length is about 5.8mm, with the 86mm it gets to about 5.8mm (or, if you prefer, the amplification due to the Barlow is 2.92x and 3.27x respectively, more or less).
Amazing views, competing with those provided by the Pentax XW 5mm and the Nagler T6 11mm with the barlow and no extenders.
The only drawback was that the claustrophobic AFOV of the Orion Explorer II eyepiece caused Jupiter to move FAST through the field of view, so I was constantly in need of touching the telescope. That annoyance was paid back by very nice, pure views when the planet was on axis.

Attached Thumbnails

• 
• 

[Starman1]

Jon, after you posted this, I did some measurements, and I came up with -73.2mm for my TeleVue Barlow. I should repeat them and try to be more accurate. Mine seems to be more like a 2.1x than 2x

Anyhow, last night seeing was much better than it has been in recent times so I had some fun on Jupiter. I actually was able to deploy a 3.5mm XW which sees the focuser very seldom, almost never. Inspired by the conversations about barlow lenses and spacers, I decided to do something with the "empty" Orion barlow bodies in the case. They are empty because their optical groups are "permanently" housed in the optical trains of my two small imaging rigs.
Anyhow, having removed the lenses, they are extenders, one adding 60mm and the other one 86mm.
I had fun with the TeleVue Barlow plus these extenders plus a cheap and often ignored Orion Explorer II 17mm. With the 60mm extender, the equivalent focal length is about 5.8mm, with the 86mm it gets to about 5.8mm (or, if you prefer, the amplification due to the Barlow is 2.92x and 3.27x respectively, more or less).
Amazing views, competing with those provided by the Pentax XW 5mm and the Nagler T6 11mm with the barlow and no extenders.
The only drawback was that the claustrophobic AFOV of the Orion Explorer II eyepiece caused Jupiter to move FAST through the field of view, so I was constantly in need of touching the telescope. That annoyance was paid back by very nice, pure views when the planet was on axis.

Tele Vue 1.25" eyepieces, by and large, have their focal planes 0.25" below the shoulder of the eyepiece.

Tele Vue Barlows are designed to be their stated magnifications with Tele Vue 1.25" eyepieces.

So, if you use an eyepiece with a focal plane at the shoulder, that focal plane will be 0.25" farther from the lens of the Barlow and thus yield a slightly higher power, like 2.1x.

 

If you'd like an easy way to tell the exact magnification factor of a Barlow with a given eyepiece, merely time the passage of a star on the celestial equator across the field of the eyepiece (do it 2 or 3 times and take the largest timing).

Do it again with the Barlow in place.

Time without Barlow ÷ Time with Barlow = magnification factor for that eyepiece.

[RLK1]

For a 2" 1.5x barlow:    https://www.surpluss...tem/l3948d.html