2 inch Barlow

[davekelley]

Hi

I have a 6 inch dob and I really like the views and the comfort with my relelation 2 inch 30mm ep. I am wondering about buying the 2 inch revelation 2x barlow it looks very nice. I see also Celestron do a 2 inch 2.5x barlow that is very lightweight and 2.5x might be a lot more useful in terms of magnification.  Also the celestron is very light in weight but in a dob that doesn't  matter too much. The celestron is quite a bit more expensive but that isn't a deal breaker.  Anyone had experience and can compare the two barlows I would be grateful thank you.  I Mostly do planets and bright DSO's from suburban garden with light pollution.

Thanks everyone

 

dave

[Cosmic Geoff]

I am not sure why you want to Barlow the 30mm eyepiece. You could simply use a 1.25" 12mm or 15mm eyepiece which would give the same magnification and be less cumbersome. Most folk only use 2" eyepieces because they can't attain the desired low-power results within a 1.25" eyepiece barrel. 

[alanjgreen]

You are right to consider Barlow of a comfortable long focal length eyepiece. But I would not go for a basic Barlow!

Look for a second hand Televue 2x2" power mate. It will leave the eye relief of your 30mm alone otherwise it could become too much with a basic Barlow.

powermates are great.

Put a wanted ad on astrobuysell. That way if you come to sell it later, you will lose very little money as they do not lose their value

[Relpet]

Bresser had a sale a while ago and I bought an ES 2x 2" Barlow.  It's a nice thing to have but I rarely use it.  With an 8" Dob and a 2" 14mm Nagler EP I can't say I get a noticeably better view than with a good quality 1.25" 7mm EP.  The combined weight of the Nagler with the Barlow is hefty and the only real benefit to my weak old eyes is the eye relief.  As Cosmic Geoff suggests, for higher magnification get the appropriate 1.25" EP.  Having said that I would love to get the chance to try the PowerMAte Alan suggests - before spending the money!

[davekelley]

It's really just that the 2" is very comfortable for me. I find most 1.25" wide angle ep's are difficult in terms of eye placement. It sounds mad to say it I have the revelation 1.25"  15mm superview and the 1.25" barlow and that 15mm is a nice ep but I love to use thwe2 inch 30mm to locate an object and it would be nice to then just pop in a barlow, without having to use the 1,25" adapter?  I have had good interesting answers so far thanks all.

 

[Louis D]

You will experience weird exit pupil aberrations and edge of field vignetting or outright cutoff with just a simple 2x barlow and a longer focal length 2" eyepiece.  You want a telecentric barlow/magnifier like a Powermate or a TV Big Barlow coupled with a Panoptic Barlow Interface (PBI) if you're going to go this route.  I went cheap and found that a 2" GSO 2x ED barlow couples perfectly with a PBI for less than $100 when both are bought used.  It absolutely gets out of the way with all 2" eyepieces, even with 40mm Meade SWA and 30mm ES-82 eyepieces.

[swamp thing]

Hi 

I use a 2" 2x powermate in my scope. Simply stunning, you don't even know it's there. Optically the powermate adds nothing but power.

The down side you may find is weight. You may find your 6" Dob doing a swift nosedive when you add such large lumps of glass and you need to counterweight it. Though this is not difficult to do it does add to the faff of swapping the eyepiece Barlow combination. 

I think that this weight problem is why so many prefer single eyepieces. I don't have this counterweighting issue as I built my scope to accommodate any eyepiece/Barlow combination without the need of them. Few commercially available scopes are.

 

[Stu]

On 07/07/2017 at 19:10, Louis D said:

You will experience weird exit pupil aberrations and edge of field vignetting or outright cutoff with just a simple 2x barlow and a longer focal length 2" eyepiece.  You want a telecentric barlow/magnifier like a Powermate or a TV Big Barlow coupled with a Panoptic Barlow Interface (PBI) if you're going to go this route.  I went cheap and found that a 2" GSO 2x ED barlow couples perfectly with a PBI for less than $100 when both are bought used.  It absolutely gets out of the way with all 2" eyepieces, even with 40mm Meade SWA and 30mm ES-82 eyepieces.

Very interesting post Louis. I had never heard of a PBI before, looks like a very clever bit of kit, discontinued now I think so has to be picked up used. I found this CN thread about it. Thanks for the post  

https://www.cloudynights.com/topic/538612-just-picked-this-up-panoptic-barlow-interface/

[John]

A barlow lens will push the eye relief of the 30mm eyepiece out beyond the eye cup so finding the correct eye positioning can be awkward. A Powermate / telecentric type focal extender does not have this effect.

Years ago I did try a Tele Vue PBI and it does the trick nicely of creating a telexteder from a conventional barlow. It works best with the TV Big barlow but it does work with other brands too.

 

[Louis D]

3 hours ago, Stu said:

Very interesting post Louis. I had never heard of a PBI before, looks like a very clever bit of kit, discontinued now I think so has to be picked up used. I found this CN thread about it. Thanks for the post  

https://www.cloudynights.com/topic/538612-just-picked-this-up-panoptic-barlow-interface/

Here another CN post on the GSO/PBI combination.

3 hours ago, John said:

It works best with the TV Big barlow but it does work with other brands too.

It only works with barlows of similar focal length.  The TV BB and GSO ED are nearly identical in this respect.  I tried the PBI with my Orion 2" 2X Deluxe barlow which is about 6 inches long and it resulted in aberrated views.  Definitely better without it in that situation.

[Relpet]

12 hours ago, Stu said:

Very interesting post Louis. I had never heard of a PBI before, looks like a very clever bit of kit, discontinued now I think so has to be picked up used. I found this CN thread about it. Thanks for the post  

https://www.cloudynights.com/topic/538612-just-picked-this-up-panoptic-barlow-interface/

If you want one they are not expensive.  A quick search showed this. 

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p8409_TeleVue-EPO-INT---Panoptik-Barlow-Interface---optimiert-Abstand.html

I may try one with my ES

[Dave In Vermont]

I wrote a similar query a year or so ago. Which, and I thank him again, Ruud answered for me. He suggested the GSO 2" 2X, saying it works very nicely.

Ruud has always given excellent advice, so I purchased one from AgenaAstro over here in the Untied Snakes for very little $$$£££'s:

http://agenaastro.com/gso-2-2x-ed-barlow-lens.html

The only problem with it was with the 1.25" to 2" adapter it comes with - the brass compression-ring was poor and popped out of it's groove, rendering it useless & broken. But I've got a drawer full of these, so I swallowed the cost and popped-in a WilliamOptics one. Now it works great! I highly recommend these! Another winning product - aside from the adapter - from GSO.

Dave

[triton1]

I use the revelation 2" ed barlow in 2" mode to get some of the higher magnifications and I find it works well,it will be abit weighty and protrude abit from the ota.These can be had quite cheap s/hand so why not buy and try.If you don't like it sell it you shouldn't lose any money.

[Dave In Vermont]

13 minutes ago, triton1 said:

I use the revelation 2" ed barlow in 2" mode to get some of the higher magnifications and I find it works well,it will be abit weighty and protrude abit from the ota.These can be had quite cheap s/hand so why not buy and try.If you don't like it sell it you shouldn't lose any money.

Hi John -

I just tracked down your Revelation 2" ED, and it's the same as the GSO - just branded 'Revelation' amongst many others I'd wager.

Another piece of the puzzle,

Dave

[cletrac1922]

Hi Dave

 

I have never been able to focus using 2" 2X barlow, even with extension tube

Have huge success using 1.25" 15mm wide angle eye piece

With club belong to, do school and space badge for scout/guide movement, and 7-9yo kids find it easier to view using a wide angle eyepiece

Happy Viewing

 

John   

[triton1]

Yes I think your right Dave the skywatchers ed is also the same but the prices do vary a lot.My brother bought me mine for the princely sum of £32.99 a couple of years ago they now sell for £70 from the same shop.I find the quality of these barlows very good and if I paid three times as much for a televue would it be three times better?To be honest I don't pay them any attention when using them it's not like they scream at you saying "your looking thru a barlow".

[Louis D]

16 hours ago, cletrac1922 said:

Hi Dave

 

I have never been able to focus using 2" 2X barlow, even with extension tube

Have huge success using 1.25" 15mm wide angle eye piece

With club belong to, do school and space badge for scout/guide movement, and 7-9yo kids find it easier to view using a wide angle eyepiece

Happy Viewing

 

John   

In what sort of scope?  If a refractor, you're best off unscrewing the optics unit and screwing it onto the front of your 2" diagonal if it removeable and threaded the same as the 2" filter thread.  The GSO/Revelation ED 2" 2x barlow works in this manner.

If in a Newt, you may actually have to pull the barlow unit up and out of the focuser to reach focus.  My 6" long Orion Deluxe 2" 2x requires about 2" of it hanging out of the focuser.  Its nosepiece is not removeable, unfortunately.

An SCT or Mak should be able to reach focus given their enormous back focus capabilities by moving the primary mirror to focus.

[Dave In Vermont]

6 hours ago, triton1 said:

Yes I think your right Dave the skywatchers ed is also the same but the prices do vary a lot.My brother bought me mine for the princely sum of £32.99 a couple of years ago they now sell for £70 from the same shop.I find the quality of these barlows very good and if I paid three times as much for a televue would it be three times better?To be honest I don't pay them any attention when using them it's not like they scream at you saying "your looking thru a barlow".

That's what I try to get across to people as regards a high-quality Barlow (or PowerMate-design): It's one that essentially is 'invisible' in the optical-pathway of from scope-to-eye. Just magnification, with dimming, scattering, or reflecting off the lens' elements. People need to bear in mind that a Barlow, etc. will magnify everything - including any defects in the Barlow itself.

The GSO (Skywatcher, Revelation, who-knows-how-many others) 2" does a pretty good job. Is that extra smidgen of 'invibility' a TeleVue® may bring worth it? That's up to the individual to answer. As for me - I'm perfectly happy with the GSO offering.

Have fun up there -

Dave

[John]

7 hours ago, triton1 said:

Yes I think your right Dave the skywatchers ed is also the same but the prices do vary a lot.My brother bought me mine for the princely sum of £32.99 a couple of years ago they now sell for £70 from the same shop.I find the quality of these barlows very good and if I paid three times as much for a televue would it be three times better?To be honest I don't pay them any attention when using them it's not like they scream at you saying "your looking thru a barlow".

3x better ? - no, how could it be ?

But having owned a Revelation / GSO 2" 2x Barlow and a few of the TV Powermates and barlows there are noticable differences IMHO. 

The Revelation / GSO items are great value though and for their cost, perform well, no doubt about that.

 

[bomberbaz]

Long time aince I have been on but noticed this thread.  

I have 3 2"eyepieces.  All top quality wide angle which i use with a 2x powermate.  

I would not change this setup as I love the huge fov and the powermate is an exceptional addition to my ep box. 

I have not bought a new eyepiece or similar in two years as the combo above cannot be beaten imho.  

Weight and balance issues are rectified ysing magnets and a spare dumbel weight as needed.  Its quite easy once you figure out what is needed. 

[Louis D]

On 7/10/2017 at 16:44, John said:

3x better ? - no, how could it be ?

But having owned a Revelation / GSO 2" 2x Barlow and a few of the TV Powermates and barlows there are noticable differences IMHO. 

The Revelation / GSO items are great value though and for their cost, perform well, no doubt about that.

 

Did you try the GSO with the TV PBI during the comparison to level the playing field?  The combo works so well for me, I see no reason to ante-up for the Powermate.