27 replies to this topic

[Jon Isaacs]

I frequently use 1.25 inch Barlows but have avoided 2 inch Barlows, in part because I've never owned a 2 inch eyepiece that I wanted to Barlow. Barlowing the 31mm Nagler just does make sense.

 

But over the last few years I've acquired the 21 mm, 13mm, 10mm and 8 mm Ethos eyepieces and I'd like to Barlow the 13mm, 10mm and 8 mm rather than investing $1500 in three more eyepieces. Technically they're 1.25 inch-2 inch eyepieces but using them with a 1.25 inch Barlow is not really practical.

 

Last month I tried my friend Bruce's 2X TV Big Barlow in the 22 inch on M2 and I decided it was time to buy a 2 inch Barlow. Bruce has made a science of using 2 inch Barlows with extenders and his 17 mm and 13mm Ethos's so I wanted to investigate that as well. 

 

With Barlows, coma correction is always an issue, Bruce has a Paracorr but doesn't use it much in his 18 inch F/4.5 Obsession.  I figured it give it a try. 

 

Unfortunately Don no longer carries the Big Barlow so I ponder my options and decided to go the inexpensive/cheap route, the Zhummel/GSO 2x 2inch. I've liked the 1.25 inch GSO Shoety's, in particular, the ability to remove the optics and thread them on to eyepieces and extensions.

 

Everyone seemed out of stock except Amazon so I reluctantly ordered it from Amazon. That was 4pm on a Sunday night. 6 am Monday morning, I went outside to get the newspaper and there it was.. 

 

The first night was from my backyard with my 10 inch Dob. It worked quite well with the three Ethos eyepieces but it was really too long to fit the Paracorr so I had to focus substantially inward. At that point I was using the Ethos eyepieces with the 2 inch expansion tubes.

 

I decided to order a shorter tube with eyepiece holder for the Barlow so I could remove the Barlow's optics and have a shorter Barlow, less magnication, but the Paracorr would not be as compromised. The shortest one I could find was 30 mm.

 

These last three nights out in the high desert, I've been experimenting with my 16 inch. So far, so good.

 

The first thing I did was remove the barrel extensions from the three Ethos's. This bought me Back focus. This combined with the shorter Barlow body allows the Paracorr spacing to be correct with the Barlow in place. Normally the 13mm and 10mm are at H, fully outward. With the Barlow, they're at A-B.  With the 8 mm, there's even more room.

 

So that works very nicely.  I drift timed the magnification, with the Short Body, I measured 1.75x.

 

Next was with the standard body, nominally 2x. With the Paracorr at A, it still required some inward focusing, compromising the coma correction. I drift timed the magnification factor, it came out about 1.94x.

 

Drift timing is a good way to assess the quality of the coma correction because you're paying close attention to a star as it drifts past the field stop. In this case I had many opportunities because I was using a stopwatch on my smartphone. I seemed to be able to reliably start it but had many failures stopping it so I'd push the button and look at it a and see it was still running

 

In my 16 inch F/4.4, the coma correction was quite acceptable even with the Paracorr 2 focused/positioned inward of the proper setting. 

 

All in all, I'm satisfied. Tonight I'm planning on giving it a try in the 22 inch. 

 

Jon

 

 

[cst4]

The barlow cell from my GSO 2" 2x barlow is a very useful piece of gear to me.  I do not use the barlow body, which is basically just an extension tube.  I have several 1.25" barlows but I more often screw this 2" barlow cell to my 2"/1.25" adapter because it is more low profile and more natural swapping out 1.25" EP's.  I use this cell to get my binoviewers to reach focus in my refractor.  I also sometimes attach it to my 2" T-adapter or an extension tube for photography of the moon and planets through my scopes.  And attaching it up further up the optical chain allows multiple magnification factors which is nice sometimes.  Money well spent in my opinion.

[rowdy388]

I also have the Zhumell labelled GSO 2" 2X barlow. I bought mine at least a dozen years ago. I can't think of anything I've

bought for astronomy that has been a better value. I've unscrewed the lens cell and barrel and used the different parts on

other eyepieces many times. The quality of the glass is very good, almost scary good for the price, which sometimes makes

me wonder why I've spent thousands on other eyepieces. Just goes to show this doesn't have to be an expensive hobby to

have quality stuff.

[PKDfan]

Hi Jon!

I am shocked it has taken you so long to get this size Barlow!

For my purposes it is invaluable as a very low scatter lunar exploration tool mated with my Baader zoom for optimal magnifications with my 4" apo.

I think you will be very pleased with it!

Congratulations.



Cs&Gs

[RLK1]

Jon,

Like your friend, why don't you try using the barlow with your eyepieces without the paracorr in place and report on the edge aberrations, too...

[Jon Isaacs]

Jon,

Like your friend, why don't you try using the barlow with your eyepieces without the paracorr in place and report on the edge aberrations, too...

 

I did that in my 10 inch F/5 the first night. The coma is definitely visible, stars are not sharp at 50%-60% off-axis.

 

There are circumstances when I "pull the Paracorr" but that's mostly at very large exit pupils with filters. I considered doing it with the Ethos eyepieces and the GSO Barlow it it were necessary.

 

But my main message here is really this:

 

I this particular case I can have my cake and eat it too, I can use the Barlow at 1.75x with these eyepieces and still have the proper Paracorr 2 spacing, no compromise.

 

And there's really no advantage in pulling the Paracorr. If I pull the Paracorr and use the Barlow, I get 1.94x Magnification. If I use the Paracorr with the shorter body I get 1.15 x 1.75x = 2.0x magnification.

 

And too, the somewhat improperly spaced Pararcorr 2 with the 2x Barlow is still quite well corrected for coma.

 

In my particular situation, the 13mm, 10mm and 8 mm Ethos are the only 2 inch eyepieces I'm interested in Barlowing. All my other medium and high power eyepieces are 1.25 inch.

 

Jon

[kongqk]

I did that in my 10 inch F/5 the first night. The coma is definitely visible, stars are not sharp at 50%-60% off-axis.

 

There are circumstances when I "pull the Paracorr" but that's mostly at very large exit pupils with filters. I considered doing it with the Ethos eyepieces and the GSO Barlow it it were necessary.

 

But my main message here is really this:

 

I this particular case I can have my cake and eat it too, I can use the Barlow at 1.75x with these eyepieces and still have the proper Paracorr 2 spacing, no compromise.

 

And there's really no advantage in pulling the Paracorr. If I pull the Paracorr and use the Barlow, I get 1.94x Magnification. If I use the Paracorr with the shorter body I get 1.15 x 1.75x = 2.0x magnification.

 

And too, the somewhat improperly spaced Pararcorr 2 with the 2x Barlow is still quite well corrected for coma.

 

In my particular situation, the 13mm, 10mm and 8 mm Ethos are the only 2 inch eyepieces I'm interested in Barlowing. All my other medium and high power eyepieces are 1.25 inch.

 

Jon

Thanks for the great review Jon! This looks very interesting, and I may try some of the 2" Barlow as well. Currently, I only used my 1.25" Barlow on my APM eyepieces. I use the 1.25X and 1.5X and screw directly on the eyepiece. For the GSO 2" eyepiece, is the bottom can be unscrew and used as a 1.5X barlow as well? 

[Jon Isaacs]

For the GSO 2" eyepiece, is the bottom can be unscrew and used as a 1.5X barlow as well?

 

 

It unscrews and threads on to eyepieces as well as adapters.

 

I don't know what the approximate magnification is.

 

Jon

[kongqk]

It unscrews and threads on to eyepieces as well as adapters.

 

I don't know what the approximate magnification is.

 

Jon

Perfect, thanks Jon. I will get one to try as well ^_^ I always think the APM eyepieces have already been very heavy and large, if it can screw to the bottom, it would be better. 

[f18dad]

Thanks for this detailed review Jon! There's going to be a run on these GSO barlows now. Glad I have mine already, as well as the shorty. They both work really well for me. Important part of the tool kit. One of life's true bargains!

[Jon Isaacs]

The particulars of this thread focus on the suitability of the GSO 2X 2 inch Barlow for use with the 13 mm, 10 mm and 8 mm Ethos eyepieces in the Paracorr 2.

 

These three eyepieces can all be used at the H setting, furthest out. The 8mm Ethos with the 2 inch TV barrel extender is actually parfocal with the 10 mm and 13 mm in the Paracorr 2.

 

What I found last night was this:

 

With the 10 mm Ethos plus the 2X Barlow, if set the Tunable Top to A, fully inward, I was nearly in focus and it required an additional one turn of the Feathertouch microfocuser to reach focus.

 

I later use a pair of calipers to determine that 1 turn of the microfocuser corresponded to 0.075" or about 2mm. The step size for the Tunable Top is 0.10" so this is slightly less than one step inward, it's like using the G instead of the H setting.

 

Last night,  I spent some time last night checking out M3 with the using the 13 mm (310x) and 10 mm (400x) with the 2x Barlow in standard form using my 16 inch F/4.4. I found the edge correction very good, stunning.. 

 

But the most awesome thing last night, and spending $60 to double the magnification of three Ethos eyepieces is pretty awesome, was star hopping to M3 and noticing something that didn't belong there in the finder, comet C/2021 A1 Leonard.

 

It's magnitude 6.8 and has a real tail.  Don't miss it.. I followed with the 16 inch into the sunrise, I still had it 45 minutes before sunrise. My SQM-L pointed at Leonard measured 16.91 mpsas, it should be visible from an urban site if you're out there early enough.

 

https://www.cloudyni...021-a1-leonard/

 

Jon

[areyoukiddingme]

I also have the Zhummel 2x, and agree on the optical quality. I've compared with the A-P baradv, and to be honest, I'd struggle to tell the difference if the test were blinded.

 

The barlow can give lower magnification by attaching to the bottom of an eyepiece directly, but the results are not pretty. Somewhere around 1.5x is probably as low as I would want to go.

 

I also barlow my ethos eyepieces (the 6 and 8), but generally prefer not to use a 2" barlow as it's quite a large contraption, especially when combined with the Paracorr. It is obviously workable, but I think probably more suitable for larger dobs than smaller.

 

The NIKON1.6x gets the most use for me. It is compact, optically excellent, and with the Ethos gives me a 5mm and 3.75, which does a nice job replacing the 3.7 and 4.7 ethos. And when combined, the size and weight is just a hair more than the ethos SX.

Edited by areyoukiddingme, 03 December 2021 - 02:04 AM.

[Jon Isaacs]

I also have the Zhummel 2x, and agree on the optical quality. I've compared with the A-P baradv, and to be honest, I'd struggle to tell the difference if the test were blinded.

 

The barlow can give lower magnification by attaching to the bottom of an eyepiece directly, but the results are not pretty. Somewhere around 1.5x is probably as low as I would want to go.

 

I also barlow my ethos eyepieces (the 6 and 8), but generally prefer not to use a 2" barlow as it's quite a large contraption, especially when combined with the Paracorr. It is obviously workable, but I think probably more suitable for larger dobs than smaller.

 

The Tak 1.6x gets the most use for me. It is compact, optically excellent, and with the Ethos gives me a 5mm and 3.75, which does a nice job replacing the 3.7 and 4.7 ethos. And when combined, the size and weight is just a hair more than the ethos SX.

 

Mine is actually the Zhummel version.

 

I agree, it's quite a contraption but seems like a good fit for a larger scope, it seems reasonable for the 16 inch and 22 inch and probably the 13.1 inch and 12.5 inch, they all have sturdy low profile focusers.

 

Jon

[Voyager 3]

I also have the Zhummel 2x, and agree on the optical quality. I've compared with the A-P baradv, and to be honest, I'd struggle to tell the difference if the test were blinded.

 

The barlow can give lower magnification by attaching to the bottom of an eyepiece directly, but the results are not pretty. Somewhere around 1.5x is probably as low as I would want to go.

 

I also barlow my ethos eyepieces (the 6 and 8), but generally prefer not to use a 2" barlow as it's quite a large contraption, especially when combined with the Paracorr. It is obviously workable, but I think probably more suitable for larger dobs than smaller.

 

The Tak 1.6x gets the most use for me. It is compact, optically excellent, and with the Ethos gives me a 5mm and 3.75, which does a nice job replacing the 3.7 and 4.7 ethos. And when combined, the size and weight is just a hair more than the ethos SX.

Can the tak be used on reflectors ? I thought it was only usable in their refractors ... Did you mean the Nikon 1.6× ? 

[areyoukiddingme]

Can the tak be used on reflectors ? I thought it was only usable in their refractors ... Did you mean the Nikon 1.6× ? 

 

Dang, yes, I meant Nikon . . . will make the change.

[kongqk]

My Zhumell 2" 2X barlow came today as well. Did a quick test, and really love it. First, it is really light weight, I was thinking it will be much heavier, it is actually almost the same weight as my 1.25" 2X TV barlow. I tested in on my ES 30 mm, with the barlow, the view on my f6 8" dob is sharp to the edge. I also tried screw the bottom to the ES 30 mm directly as a 1.5X barlow, I can see the edge 20-30% is really blur, also, it can not focus unless an extension tube used or pull the ES 30 mm a little out. I also tested on my APM 7 mm to barlow it to 3.5 mm and directly compare with my APM 3.5, though the condition is not perfect, I can not get the sharpest images from both. Comparing them on M15, I don't see too much difference, and on Jupiter, I feel using the APM 3.5 mm directly is a little shaper than the 7 mm barlowed to 3.5 mm on the bands, but very subtle. Anyway, I think I will keep it and use it for the ES 30 barlow to 15 mm. I will consider more if I sell the APM3.5 or not if I can barlow the 7 mm to similar view.  

 

EDIT: I also like the 2 to 1.25" adapter, it is recessed, and not eat the in travel distance, I think this will help in some of the cases when I don't have enough in travel focus (like the Turret). 

Edited by kongqk, 04 December 2021 - 11:16 PM.

[kongqk]

Also, anyone knows why using the 1.5X barlow on my ES 30 mm, the view on the edge becomes worse. I always thought the barlow is essentially make the scope slower (f/6 with 2X barlow is f/12, and with 1. 5X barlow is f/9), I expected the view with the 1.5x barlow cleans up a little of the edge without the coma corrector, but it is opposite (the 2X + ES 30 mm indeed makes the edge cleaner). 

[Letterman]

I also use a GSO 2" 2X power barlow lens cell screwed into a 2" to 1-1/4" adapter on occasion. I used a Celestron 8-24mm zoom set to 8mm as a test eyepiece.This adapter by itself is 30mm long. The barlow's back lens is recessed about 2mm below the end of the adapter when it is fully screwed in, hence the extra 2mm of clearance. When used in this configuration, the combo functions as a 1.42X barlow by my quick calculation. Other eyepieces my vary.

 

I also have an adapter that has a recessed cup for the 1-1/4" eyepiece, but I don't use that one since there is a higher chance that the 1-1/4" eyepiece may hit the barlow lens. The slightly longer adapter provides 32mm of clearance between the barlow lens glass and the top of the adapter.  If you use an similar adapter combo, then carefully measure how much clearance you have before you insert a 1-1/4" eyepiece to avoid scratching the glass.

[Jon Isaacs]

Also, anyone knows why using the 1.5X barlow on my ES 30 mm, the view on the edge becomes worse. I always thought the barlow is essentially make the scope slower (f/6 with 2X barlow is f/12, and with 1. 5X barlow is f/9), I expected the view with the 1.5x barlow cleans up a little of the edge without the coma corrector, but it is opposite (the 2X + ES 30 mm indeed makes the edge cleaner). 

 

I don't know exactly why it happens but happens sometimes with certain eyepieces when the optics from a 2x Shorty is too close to the eyepiece. With the ES 30mm it's not hard to imagine, the Barlow is very close to the Smyth lens in the barrel.  The Smyth lens is trying to do something but the Barlow is doing something else.

 

It happens with the Meade 24 mm Series 5000 SWA with the 1.25 inch Shorty. 

 

Jon

[kongqk]

I don't know exactly why it happens but happens sometimes with certain eyepieces when the optics from a 2x Shorty is too close to the eyepiece. With the ES 30mm it's not hard to imagine, the Barlow is very close to the Smyth lens in the barrel.  The Smyth lens is trying to do something but the Barlow is doing something else.

 

It happens with the Meade 24 mm Series 5000 SWA with the 1.25 inch Shorty. 

 

Jon

Thanks Jon for the explanation. I will do some more testing on some shorter FL eyepieces, and see how it works.  

[RLK1]

Anybody try screwing the 2" GSO barlow onto the bottom of the paracorr instead of the eyepiece? While my 2" GSO barlow will not quite match the threads of my astrosystems 1.25"/2" low profile adaptor, I find it will easily screw onto the bottom of the paracorr. I intend to try that combo with my stellarview binoviewer to see if allows for focus in my 16"4.5 dob at a lower magnification than my omni 1.25" barlow which performs more like a 3x plus barlow given the optical-mechanics of the binoviewer in the dob. 

[Thomas_M44]

Just for the record: I presently have all current TV Barlows except the 2-inch Big Barlow. I also have all TV Powermates except the 2X (which is on my future acquisitions list).

 

I relatively recently obtained  the 2-inch GSO 2X ED Barlow, and I am stunned by the quality and performance to price ratio of the unit ($65). In fact,  I feel this GSO Barlow is an excellent piece of optic in overall terms, regardless of price. It’s not going to cause me to sell any of my TV Powermates or Barlows, but it has a very useful range of application for me and fills some uses better than any other amplifier I own. 

 

I use the GSO 2-inch 2X Barlow in my 150mm f/6 Newtonian most often lately. For me, it’s a “keeper”.

Edited by Thomas_M44, 07 December 2021 - 04:43 AM.

[Blacksmith]

just curious have you tried it with your 34mm 72° eyepiece?

[Starman1]

Unfortunately Don no longer carries the TeleVue Big Barlow 

Jon

Not in stock, but available on request, like all TeleVue items.

 

Anybody try screwing the 2" GSO barlow onto the bottom of the paracorr instead of the eyepiece? While my 2" GSO barlow will not quite match the threads of my astrosystems 1.25"/2" low profile adaptor, I find it will easily screw onto the bottom of the paracorr. I intend to try that combo with my stellarview binoviewer to see if allows for focus in my 16"4.5 dob at a lower magnification than my omni 1.25" barlow which performs more like a 3x plus barlow given the optical-mechanics of the binoviewer in the dob.

 

Let us know what magnification results.

[Jon Isaacs]

just curious have you tried it with your 34mm 72° eyepiece?

 

I have..

 

I think I was using the 16 inch F/4.4 without the Paracorr. As one might expect, it improved the views quite noticeably, much better a F/8.8 than at F/4.4.

 

It makes sense with a relatively lightweight eyepiece like the 34 mm Svbony. It doesn't make much sense with the 31 mm Nagler.. too much weight out too far.

 

Jon