Barlow lens.

[bandsman]

What size Barlow lens is most suitable to go with my astromaster 130 & helios hyperflex 9-27mm  zoom eyepiece, I don't want to make a bad call and end up regretting my purchase, any suggestions would be most helpful.

 

[Second Time Around]

I'd recommend a dual 1.5x/2x model as this gives much more flexibility.  Not all 2x Barlows allow this, but the ones that do so don't cost any more.  These ones allow the black lens cell to be unscrewed from the body of the Barlow and then screwed into the filter thread at the bottom of an eyepiece.  Very often this won't be in the blurb, but FLO do one in their Astro Essentials range that even has a standard T thread at the top for attaching a camera.  It's just £25. 

The exact amplification varies from eyepiece to eyepiece depending on where the field stop is located.

Go to https://www.firstlightoptics.com/barlows/astro-essentials-125-2x-barlow-with-t-thread.html

[Tiny Clanger]

Hello and welcome,

I agree with Second Time Around  a 2x Barlow is fine . With your zoom eyepiece the  1.5x facility 1.5x would yield  6mm - 18mm, the 2x will give you the range 4.5mm - 13.5mm .

Your scope has a theoretical limit of 260x magnification using the usual rule of thumb ( twice the aperture in mm ) , a more realistic maximum for most conditions is rather less than that, maybe 160 or 180x

Your 'scopes focal Length is 650mm. To find the magnification divide focal length of scope by eyepiece rating (both in mm) so with the 2x Barlow and your zoom at 9mm you will get a maximum of 144x which is a reasonable highest power for the odd time when the sky is steady enough for it. 

If you were thinking about a 3x barlow, that would push your 'scope (and the uk skies !) to 216x, which would probably be too much magnification to ever be practically useful .

Heather

[AlexK]

Your focal is 650mm, so
9 - 27 zoom = 72x - 24x

I'd rather go with a 3x Barlow which will give you exactly the missing higher mags range:
3 - 9mm = 216x - 72x

The max magnification for a cheap instrument is indeed 2D (Heather is right) but if you are lucky your mirrors might be from a better batch, so under ideal sky you can push to 2.5D (~300x). I do even higher (2.75D)! 

The 3x is most viable anyway why would you want intersecting magnifications afterall?

Don't bother getting an expensive one for a 3x, just avoid total nonames. E.g. a $40 Meade 3x would be totally adequate.

 

Edited February 9, 2021 by AlexK

[Second Time Around]

16 minutes ago, AlexK said:

Your focal is 650mm, so
9 - 27 zoom = 72x - 24x

I'd rather go with a 3x Barlow which will give you exactly the missing higher mags range:
3 - 9mm = 216x - 72x

The max magnification for a cheap instrument is indeed 2D (Heather is right) but if you are lucky your mirrors might be from a better batch, so under ideal sky you can push to 2.5D (~300x). I do even higher (2.75D)! 

The 3x is most viable anyway why would you want intersecting magnifications afterall?

Don't bother getting an expensive one for a 3x, just avoid total nonames. E.g. a $40 Meade 3x would be totally adequate.

 

The field of view of all but a few very expensive zooms is significantly lower at the long focal lengths.  This means that if for instance you wanted a magnification at say 144x (i.e. the maximum with a 9-27mm zoom at 9mm plus a 2x Barlow), the field of view would be much wider than with the zoom set at 13.5mm with a 3x Barlow (that would yield the same 144x).

As I mentioned earlier, your scope isn't designed for very high magnifications.  This is largely because the 102mm objective lens is just a 2 element achromat with a fast focal ration of f/6.5, plus the scope is on a lightweight mounting.  It does however mean that for it's price you get a refractor with which you can see fainter objects.

Alex comes from California where skies are likely to be considerably less turbulent in the high latitude of the UK, where we're frequently under the jetstream.  So that probably explains Alex's experiences of being able to use higher magnifications, that as Heather said, would rarely be possible with your scope over here.

[AlexK]

You are right about California, Steve. The pristine sky is not that rare here in comparison. However, I spent 20 years of my "amateur career" at the latitude of London (Russia, Novosibirsk). Great sky is possible there too (I understand on an island it's even worse, but still). Yes, maybe just once a year, and maybe just for a couple of seconds. But if that's happened to be a Jupiter's view, even a 110mm reflector views are breathtaking then, an I remember a dozen of these down to split second on planets still, 20+ years later. By the way, the Astromaster 130 which bandsman has is a 1:5 reflector actually not a 102mm refractor you are using as an example. Sure thing, the bottom limit for planets is a 150mm, but 130 is already very close to bet on 2.5D zooms with it. At any rate, with a 3x barlow there is nothing to lose, while anything else will be just a wasted redundancy with that particular Zoom eyepiece (not necessarily so with a random set of fixed eyepieces indeed).

Regarding the AFOV, it's actually expanding as you zoom in, so with a 2x Barlow (with intersecting zooms) you will have a smaller field at the same magnification as without Barlow (which is a nonsense to do or desire).

Edited February 9, 2021 by AlexK

[John]

I use the Baader 2.25x barlow with my Hyperflex 7.2mm - 21.5mm zoom eyepiece and they work very well together to create a 9.55mm - 3.2mm zoom. The Baader 2.25x looks quite basic but has good optical element within it's plain exterior. They are just £39 new but can be picked up used for £25 or so:

https://www.firstlightoptics.com/barlows/baader-classic-q-225x-barlow.html

 

 

 

[Second Time Around]

1 hour ago, AlexK said:

You are right about California, Steve. The pristine sky is not that rare here in comparison. However, I spent 20 years of my "amateur career" at the latitude of London (Russia, Novosibirsk). Great sky is possible there too (I understand on an island it's even worse, but still). Yes, maybe just once a year, and maybe just for a couple of seconds. But if that's happened to be a Jupiter's view, even a 110mm reflector views are breathtaking then, an I remember a dozen of these down to split second on planets still, 20+ years later. By the way, the Astromaster 130 which bandsman has is a 1:5 reflector actually not a 102mm refractor you are using as an example. Sure thing, the bottom limit for planets is a 150mm, but 130 is already very close to bet on 2.5D zooms with it. At any rate, with a 3x barlow there is nothing to lose, while anything else will be just a wasted redundancy with that particular Zoom eyepiece (not necessarily so with a random set of fixed eyepieces indeed).

Regarding the AFOV, it's actually expanding as you zoom in, so with a 2x Barlow (with intersecting zooms) you will have a smaller field at the same magnification as without Barlow (which is a nonsense to do or desire).

Whoops, sorry, I did muddle up the scope!  That will indeed take a higher magnification. Perhaps I shouldn't have taken my medication early!

I'm not comparing a 2x Barlow with no Barlow though.  Rather I'm comparing it with a 3x Barlow.  

To get 144x with the 2x Barlow you'd be at the shortest focal length of the zoom (i.e. 9mm), where the apparent field of view (AFOV) is widest. With a 3x Barlow you'd be in the middle of the range of focal lengths (13.5mm) where the AFOV is narrower.  

The result is that for a zoom at a given magnification you'd get a wider true field of view with a 2x Barlow than a 3x Barlow. 

 

 

 

Edited February 9, 2021 by Second Time Around
Typo

[Second Time Around]

3 minutes ago, John said:

I use the Baader 2.25x barlow with my Hyperflex 7.2mm - 21.5mm zoom eyepiece and they work very well together to create a 9.55mm - 3.2mm zoom. The Baader 2.25x looks quite basic but has good optical element within it's plain exterior. They are just £39 new but can be picked up used for £25 or so:

https://www.firstlightoptics.com/barlows/baader-classic-q-225x-barlow.html

 

 

 

I agree that the Baader 1.3/2.25x Q Barlow would be a good bet.

However, I found it doesn't work with all eyepieces at 1.3x.  IIRC it needs 15mm of space at the bottom of the barrel, plus enough of the barrel needs to be threaded.

It obviously fits John's 7.2-21.5mm Hyperflex.  I gave my 9-27mm Hyperflex (that the OP has) to my grandkids, and no longer have my Q Barlow so can't test the combination.

Can anyone else help please?

[Tiny Clanger]

Assuming this is the 'scope in question

https://www.argos.co.uk/product/9338821

Celestron claims a somewhat optimistic  "Highest Useful Magnification:307x"

I think I'd probably disagree with their definition of 'useful' !

Heather

[John]

3 minutes ago, Second Time Around said:

I agree that the Baader 1.3/2.25x Q Barlow would be a good bet.

However, I found it doesn't work with all eyepieces at 1.3x.  IIRC it needs 15mm of space at the bottom of the barrel, plus enough of the barrel needs to be threaded.

It obviously fits John's 7.2-21.5mm Hyperflex.  I gave my 9-27mm Hyperflex (that the OP has) to my grandkids, and no longer have my Q Barlow so can't test the combination.

Can anyone else help please?

It only works in 1.3x mode with eyepieces with no lens elements within the 1.25 inch barrel. Zooms usually have a sliding set of optics within their barrels so it's no go with those and many other designs with wide fields and / or long eye relief. So I use it as a 2.25x only with my zoom.

Still a good barlow at the price even if it is just used in 2.25x mode in my view

[AlexK]

1 hour ago, Second Time Around said:

To get 144x with the 2x Barlow you'd be at the shortest focal length of the zoom (i.e. 9mm), where the apparent field of view (AFOV) is widest. With a 3x Barlow you'd be in the middle of the range of focal lengths (13.5mm) where the AFOV is narrower.  

The result is that for a zoom at a given magnification you'd get a wider true field of view with a 2x Barlow than a 3x Barlow. 

Gotcha. You are correct on the latter.

My point is just that having same magnifications as your eyepiece is already providing being repeated with the 2x Barlow on half of the Zoom EP range is not beneficial in any way as no-Barlow views will be better (at every duplicated by the 2x Barlow magnification) and can be perceived as the 1/2 of the Barlow's price waste  3x Barlow cannot provide same magnifications as that 9-27 Zoom EP. So no duplicated magnifications, zero waste.

Thus still: if planets (or other bright compact objects i.e. PNs, as well as Moon and Sun) magnification is the goal of bumping the zoom with a Barlow, I'd go with the 3x here and only here no single doubt. These minor FOV variations doesn't matter much for that if at all. Especially as the scope is on the GEM with "micrometers".

Edited February 10, 2021 by AlexK

[AlexK]

2 hours ago, Tiny Clanger said:

Assuming this is the 'scope in question

https://www.argos.co.uk/product/9338821

Celestron claims a somewhat optimistic  "Highest Useful Magnification:307x"

I think I'd probably disagree with their definition of 'useful' 

That's nothing to agree or disagree with as it's not "a highest useful magnification" but "The Highest Useful Magnification"   Which is just a long settled telescope specifications terminology: "The Highest Useful Magnification of a telescope equals the telescope primary aperture diameter in inches multiplied by 60". More modest China scope manufacturers knowing their poor quality and afraid of claims had it modified to "... by 50" (just kidding ), which corresponds to 2xD mm.

Just to quote it with more explanation: https://www.astronomics.com/info-library/how-to-pick-an-eyepiece/highest-useful-magnification/

And the test: 307/60 = 5.117",  * 25.4mm = 129.97mm

So, as I have already mentioned above, very high magnifications are working with small(ish) instruments. You just have to be very prepared, extremely observant, patient, and observe often to actually catch these rare occasions.

Edited February 10, 2021 by AlexK

[Tiny Clanger]

47 minutes ago, AlexK said:

That's nothing to agree or disagree with as it's not "a highest useful magnification" but "The Highest Useful Magnification"   Which is just a long settled telescope specifications terminology: "The Highest Useful Magnification of a telescope equals the telescope primary aperture diameter in inches multiplied by 60". More modest China scope manufacturers knowing their poor quality and afraid of claims had it modified to "... by 50" (just kidding ), which corresponds to 2xD mm.

 

Neither definite or indefinite article precedes "highest useful magnification : 307x " on the skywatcher website or in my quote of it.

Can't quite see how twice the diameter in mm of the 'scope in question (2x130) comes to 307 either.

[AlexK]

5 hours ago, Tiny Clanger said:

Neither definite or indefinite article precedes "highest useful magnification : 307x " on the skywatcher website or in my quote of it.

Can't quite see how twice the diameter in mm of the 'scope in question (2x130) comes to 307 either.

2x130mm (= 260x) corresponds to the 50xDinch. How? because 1inch is approx. 25mm => 50xDinch/25mm = 50/25xDmm = 2xDmm.
While 307x to 60xDinch. so it will correspond to metric 2.4xD, i.e. 2.4*130 = 312 (307 is just more precise inch/mm conversion as in fact it should be 2.362xDmm) 

(perhaps, you started answering when I've been adding the 307x test to my post above; check it out again if still confused).

Re terminology: I'm not a linguist, but "Great Britain" on the road sign means "the Great Britain is ahead". While "unpaved road" sign means "an unpaved road is ahead". No? Even the words capitalization is just a random feature in your Celestron quote? I'm not a native speaker as you have probably noticed already , but the technical terminology logics behind the quoted Celestron technical specifications sheet is clear to me.

Edited February 10, 2021 by AlexK
replaced D" to Dinch for better clarity.

[Tiny Clanger]

...

Edited February 10, 2021 by Tiny Clanger
waste of effort.

[AlexK]

6 hours ago, Tiny Clanger said:

...

No problem. Just check that https://www.astronomics.com/info-library/how-to-pick-an-eyepiece/highest-useful-magnification/ link and treat that as an axiom.

The common misconception is that at too high a magnification like 2.4Dmm everything always looks blurry. That's true most of the time due to the local atmosphere turbulence. However the turbulence is not something permanent at all. There are rare moments it's extremely steady and the trained eye is capable of recognizing a lot of details in a split second (contrary to any cameras even after meticulous stacking of millions of frames). That's why when observing planets you must watch that blurry blob long enough to have a chance catching every such moment. In my experience 30 min is the minimum if the seeing is not ideal. Thus you want either a GEM with fine manual or motorized tracking, or a properly built Dob + experience for smooth manual tracking, and an observer's chair. As even a slight jitter of the view at a high magnification when you are guiding could happen exactly at that split second when the view is truly cosmic at 800x magnification, so you may never even notice it's ever happened. I know many seasoned amateurs who never saw swirling clouds in the belts of Jupiter with their own eyes observing it for many decades just because they were blindly following the "2D rule of thumb" and didn't want to do the observing work looking just for an immediate eye candy treat.

Edited February 10, 2021 by AlexK

[Louis D]

49 minutes ago, AlexK said:

As even a slight jitter of the view at a high magnification when you are guiding

However, I've noticed that when binoviewing, lightly tapping my Dob's tube at high power can sometimes allow me to recognize fine details more easily for the same reason it is easier to see a camouflaged animal in motion than when still.  It spuriously kicks-in my brain's motion processing centers.

[AlexK]

50 minutes ago, Louis D said:

However, I've noticed that when binoviewing, lightly tapping my Dob's tube at high power can sometimes allow me to recognize fine details more easily for the same reason it is easier to see a camouflaged animal in motion than when still.  It spuriously kicks-in my brain's motion processing centers.

That's true. We are predators after all, contrary to some opinions. But if the seeing is not there yet bino or artificial shaking wouldn't work on planets anyway. Perhaps, bino also promoting the eyes specialization when necessary. I.e. one eye is used for guiding/tracking body control feedback, another for actual observing of the target's behavior. But that's already a much higher level of the observing expertise, carved into the habit from hundreds hours of observing. Guiding a shaky mount at the very high zoom usually consumes all the attention of a beginner so not to lose it from a random shivering and having to start over from a lower zoom. 

By the way, for the mono view, that "shaking/rocking" technique is especially useful for very tough DSOs in the peripheral vision.

To stay on topic: Any Barlow actually can be easily converted to a higher zoom rate Barlow with an extender tube. E.g. by screwing together two EP barrels. So if the OP is in the analysis-paralysis or denial state after this lengthy chat, feel free to go with the 2x Barlow having an unscrewing lens end (just for the higher versatility) 

While on a side note, I would ask why 2x Barlows actually existing, when the rule of thumb for the perfect EPs collection is the 2x ramp as well? I'd rather have a 1.5x, 2.5x, or 3x Barlow to extend my perfect EPs collection with more in-between zoom levels variety (not me, but kinda more logical desire than having same zooms with the Barlow for all EPs but the shortest one).

Edited February 10, 2021 by AlexK

[Second Time Around]

19 hours ago, AlexK said:

To stay on topic: Any Barlow actually can be easily converted to a higher zoom rate Barlow with an extender tube. E.g. by screwing together two EP barrels. So if the OP is in the analysis-paralysis or denial state after this lengthy chat, feel free to go with the 2x Barlow having an unscrewing lens end (just for the higher versatility) 

For 1.25 inch Barlows I have two of the following 18.5mm extension tubes from Baader: https://www.baader-p...2-part-05).html

For 25mm go to https://www.365astronomy.com/Extension-Tube-with-1.25-Filter-Thread-25mm-long.html

For 30mm go to https://www.omegon.eu/extension-tubes/omegon-1-25-30mm-extension-tube/p,33231

Links repaired. 

Edited February 11, 2021 by Second Time Around

[Louis D]

Back on topic, I would recommend a 2x Barlow simply because I've found them to be more usable on more occasions than 3x Barlows.  I can't remember the last time I used my 3x Barlow.  It got so little use, I retired it to a box of little used astro accessories.

As for the type, the GSO 1.25" 3- element 2.5X APO Barlow lens is affordable and well regarded.  Most reports peg its actual magnification at around 2.1x to 2.2x.  It's also sold as Apertura, TPO, TS Optics and Revelation Astro.  I've read @John much prefers the Baader 2.25x Q-Turret barlow, so I would defer to him on this point.

My personal favorite is the 1990s Meade 4000 140 APO 2x Barlow.  It's also a three element design.  However, it has a removable optics section that can be threaded onto eyepieces for lower magnifications of around 1.6x.  I've measured it to be closer to 2.4x when used as designed.  They come up quite often here in the US on the astro classifieds for $40 to $50.  They might show up second hand on your side of the pond as well.

Edited February 10, 2021 by Louis D

[AlexK]

9 hours ago, Louis D said:

Back on topic, I would recommend a 2x Barlow simply because I've found them to be more usable on more occasions than 3x Barlows.  I can't remember the last time I used my 3x Barlow.  It got so little use, I retired it to a box of little used astro accessories.

You've probably missed the point that the OP's goal is to extend the versatility of his particular Zoom eyepiece as much as possible. Thus, general Barlow use cases aren't exactly applicable here if at all. A 3x Barlow would be still a better idea. But a 2x would be OK with the additional extender(s), and possibly in the long run, when deficiencies of a Zoom EP become apparent to him.

[alex_stars]

My favourite Barlow is the

Baader Hyperion Barlow

• it goes right into the Hyperion and Morpheus EPs
• fits any other 1.25" EP with its small adapter (fits nicely onto the Hyperflex zoom as a screw-on Barlow, even though the EP gets rather long)
• and has a T2 adapter, which is perfect for imaging. There you can get crazy with T2 extensions and get all kinds of magnifications. I use a 40 mm T2 extension regularly for imaging.