To Barlow or not to Barlow

expon (Jas) · #1 31-03-2014, 05:56 PM

Hello again

Recently i've been looking to acquire more eyepieces. But I have come to the question "is a barlow worth it"? There seems to be speculation over if more lenses is better than having a barlow. I have an F5 scope and it appears that a barlow can assist in some of the issues with wide angle lenses and fast scopes. However there has to be some draw backs to it but I cannot find any real reason to not go with a barlow lens.

Is a 12mm scope 2x barlowed the same as a 6mm? do barlows really affect the performance of the lens attached to it?

Amaranthus (Barry) · #2 31-03-2014, 06:00 PM

Well, it's a personal thing, but a good-quality Barlow should NOT (noticeably) affect image quality, and it preserves ER.

I have a 2.5x TV PowerMate that I use regularly for my high-power work. It is essentially invisible, parfocal across EPs, and pairs up with my 16, 11 and 9 mm Naglers beautifully (I don't generally use it on my 24 Panoptic). As such, I have no need to go any shorter on my EP FL thanks to the PowerMate. It is also useful for planetary imaging!

astro744 · #3 31-03-2014, 07:07 PM

A good quality Barlow is essentially 'invisible' and does indeed multiply the magnification by the Barlow factor. However the eye relief is extended on a Barlow to a point whereby longer focal length eyepieces become unusable.

A Powermate is a 4 element Barlow and has the advantage in that the eyepiece sees the same light cone for which it was designed and thus the eye relief is not altered and there is no vignetting.

See http://www.televue.com/engine/TV3b_p...k#.Uzkfq6iSySo for a good explanation on Barlows and Powermates and the differences between.

See also http://www.televue.com/engine/TV3b_p...k#.UzkhyaiSySo which is specifically on Barlows. (The first link above is a very good read).

OzStarGazer · #4 31-03-2014, 07:33 PM

No, a good Barlow lens will not affect the quality of the image, as others have said. However, 3x Barlow lenses don't work so well with all telescopes. The most popular Barlows are the 2x Barlows.

Marios (Marios) · #5 31-03-2014, 07:52 PM

If EP cost is driving you towards a Barlow then consider a quality zoom eyepiece to cover a good array of useful magnifications.
Once you find the sweet spots for your scope, it would be worth buying a high quality EP that you will use often. Just my 2 cents...

expon (Jas) · #6 01-04-2014, 12:33 AM

I do not have any 2" EPs however a 2" barlow would keep my options open for the future. Is there any difference to using a 1.25" EP with a 1.25" barlow over a 2" with an adapter? (other than the cost)

Varangian (John) · #7 01-04-2014, 07:19 AM

who wants mess around in the dark screwing on barlows to the negative lens of a 12mm when you can just purchase a decent 6mm ep for roughly the same price?

julianh72 (Julian) · #8 01-04-2014, 07:53 AM

Quote:

Originally Posted by Varangian

who wants mess around in the dark screwing on barlows to the negative lens of a 12mm when you can just purchase a decent 6mm ep for roughly the same price?

Or...

Who wants to turn the standard kit of two eyepieces that they got with their telescope into effectively four eyepieces, for less than the price of one new eyepiece?

E. G. 25 mm plus 10 mm effectively becomes 25 mm, 12.5 mm, 10 mm, 5 mm.

(Plus, when you DO buy a lovely new eyepiece, you'll effectively be getting two!)

OzStarGazer · #9 01-04-2014, 09:52 AM

Well, you can also attach the Barlow to the eyepiece before starting your session. This way you don't have to mess around AND you can use the Barlow with any eyepiece before any session...

astro744 · #10 01-04-2014, 09:58 AM

Quote:

Originally Posted by Varangian

who wants mess around in the dark screwing on barlows to the negative lens of a 12mm when you can just purchase a decent 6mm ep for roughly the same price?

Quote:

Originally Posted by OzStarGazer

Well, you can also attach the Barlow to the eyepiece before starting your session. This way you don't have to mess around AND you can use the Barlow with any eyepiece before any session...

A Barlow slips into the focuser just like any other eyepiece. The eyepiece then slips into the Barlow like it does into the focuser. If you are using Barlows that screw onto the bottom of eyepieces (I'm not aware of any but I'm sure they exist) I would be using a different Barlow. You cannot go wrong with the Tele Vue 2x in either 1.25" or 2".

julianh72 (Julian) · #11 01-04-2014, 10:32 AM

Quote:

Originally Posted by astro744

A Barlow slips into the focuser just like any other eyepiece. The eyepiece then slips into the Barlow like it does into the focuser. If you are using Barlows that screw onto the bottom of eyepieces (I'm not aware of any but I'm sure they exist) I would be using a different Barlow. You cannot go wrong with the Tele Vue 2x in either 1.25" or 2".

My 2x Shorty Barlow is a bit like this one:

http://agenaastro.com/gso-1-25-2x-ac...rlow-lens.html

In normal use, the Barlow just drops into the focuser / diagonal, like any eyepiece, and your eyepiece then drops into the Barlow, just like an ordinary eyepiece holder - easy as!

However, it has a couple of other tricks up its sleeve:

The Barlow lens module can be unscrewed from the base of the tube to give a "lens-less extension tube" (the top of which is threaded for a T2 mount - a handy way to attach my DSLR camera body to the scope), and a 1 1/4" threaded Barlow lens module which can be screwed into the filter thread of a 1 1/2" eyepiece. When screwed to an eyepiece, it works as a 1 1/2 x Barlow, so I guess I should modify my earlier comment:

Who wants to turn the standard kit of two eyepieces that they got with their telescope into effectively six eyepieces, for less than the price of one new eyepiece?

E. G. 25 mm plus 10 mm effectively becomes 25 mm, 16.5 mm, 12.5 mm, 10 mm, 6.5 mm, 5 mm.

(Plus, when you DO buy a lovely new eyepiece, you'll effectively be getting three!)

raymo · #12 01-04-2014, 12:38 PM

My SW80degree 2" 15 and 30mm have a 1.5x screw on barlow.
raymo

Varangian (John) · #13 01-04-2014, 04:27 PM

Quote:

Originally Posted by julianh72

Or...

Who wants to turn the standard kit of two eyepieces that they got with their telescope into effectively four eyepieces, for less than the price of one new eyepiece?

E. G. 25 mm plus 10 mm effectively becomes 25 mm, 12.5 mm, 10 mm, 5 mm.

(Plus, when you DO buy a lovely new eyepiece, you'll effectively be getting two!)

A televue barlow will cost you $200. An ES / Pentax XF / Radian will cost you the same. Regardless of how the barlow attaches (yes there are smooth sides and screw on) the fact that you remove the eyepiece, loosen the barlow screw, slip the eyepiece in, tighten barlow screw and then reinsert into the focuser is a nuisance in the dark. Better to remove said eyepiece insert different eyepiece.

The other issue with barlows is the free movement that you find in anything other than the top line ones. If the barlow does not have a screw to stabilise the EP the free play can be annoying and can affect your viewing pleasure, added to this there is the possibility that the EP can slip out.

Astro_Bot · #14 01-04-2014, 04:36 PM

I've had three barlows for visual, and got rid of them all. In my experience, they caused loss of contrast and made finding the best focus more difficult (the focal point was more "dispersed"). I now use shorter focal length eyepieces, which "snap" to focus, and enjoy a higher quality view.

I recently acquired a Powermate but that's only for planetary photography.

OzStarGazer · #15 01-04-2014, 07:21 PM

I guess not all Barlows have the same construction, but one thing which is cool about the standard ones is that if you unscrew the lens it can also be used as a T-adapter. I noticed this and was surprised (I am a newbie!) because it was not mentioned in the description when I bought it, although it is obviously a bonus, then I had a look on the net and the net confirmed what I thought.

The Mekon (John Briggs) · #16 01-04-2014, 07:50 PM

Not to barlow, that is the short answer. Better to invest in eyepieces.

barx1963 (Malcolm) · #17 01-04-2014, 10:36 PM

I am not a big fan of barlows. Mainly fiddly in the dark, but also I find most times if I want more power I don't really need 2x. Moving from a 17mm to a 13 or 10mm is usually all I need. Also I have never seen a better view in a barlowed EP than I could get with a high quality stand alone, and I have only ever used TV ones. Had a TV 2x and a TV 2.5x Powermate and ended up selling both of 'em.

Malcolm

julianh72 (Julian) · #18 02-04-2014, 12:24 AM

Not wanting to contradict the good advice from the experienced forum members here, but I'd just like to point out that this thread is in the BEGINNERS Equipment Discussion. As such, we're mainly talking about first-time telescope owners, who probably have one or two modest (hopefully reasonable) eyepieces, such as a 25 mm and a 10 mm. They're keen to see how much useful magnification they can get out of their telescope (and many will be disappointed!), and they haven't yet specialised on any particular class of targets - they want to see it all!

I maintain that a reasonable quality 2x Barlow is a good investment for such new telescope users, because it effectively expands their eyepiece selection for a very modest outlay. If / when they have worked out that a 5 mm (or whatever) eyepiece would be "just right" for their favourite targets, THAT would be the "right" time to outlay a few more dollars on one or two really good eyepieces.

raymo · #19 02-04-2014, 12:56 AM

I'm with you 100% Julian. I refrained from joining in this thread because
this subject has been discussed ad nauseum in other threads, but I have to say that the people who dislike barlows for whatever reason, tell us
all about what they think is bad about them, and studiously avoid
mentioning their benefits. Some balance would be good.
raymo

Astro_Bot · #20 02-04-2014, 01:11 AM

OK then ...

When I was a novice, I thought barlows were a good idea.

I bought my first and thought it was so-so.

I sold it and bought a second. It was slightly better, but not as good as I expected.

I sold that and bought a third and it was the best of the three, but now I had shorter f/l eyepieces for direct comparison, I concluded that barlows aren't worth it.

Now I don't use barlows for visual at all.

People new to astronomy are welcome to go through the same expensive learning experience themselves, or perhaps they can take the advice of those who've made the mistakes already ... which is kinda what this forum is for, isn't it?. Their choice, I suppose.