New EP or just a Barlow?

[emadmoussa]

The choice is either to pay £80 to get a 7mm planetary eyepiece or just buy a 2" ED Barlow for half the price.

I'm aware more glass reduces light transmission, but how much on average?

I'd rather settle for an EP, but the budget is tight, hence the question. 

[vlaiv]

I think barlow offers more flexibility, I for one find it useful for providing more eye relief with some eyepieces, but yesterday while doing some research, I stumbled upon a review of ES telecentric lens and reviewer compared it to 2" ED barlow.

From what I've read, don't think 2" ED barlow is good investment. Maybe you should spend some time researching what is best barlow for your money, or perhaps someone will offer advice here on best option.

[emadmoussa]

I had an ED Barlow once, but was forced to sell all my kit before I even tried it. So, not sure what to expect. 

[michael.h.f.wilkinson]

I personally prefer using different EPs on planets , rather than faffing around with a Barlow (or even the better tele-centrics, like TV PowerMates, or Meade TeleXtenders I have for imaging). My planetary EPs are all par-focal, or have been made so with a suitable ring, and that means that I do not have to refocus when switching magnification, e.g. due to changes in seeing. With a Barlow or tele-centric I need to refocus a lot, which takes up valuable observing time. Of course, the luxury of having a range of planetary EPs comes at a cost, and a Barlow does add flexibility

[mikeDnight]

I'm a big fan of using Barlow lenses, but I'm not sure I'd ever find a use for a 2" version. Most 2" eyepieces are fairly long focal lengths, so there's not much to be gained by halving their focal length. For lunar and planetary most 1.25" eyepieces of relatively short focal length, can be used to real advantage to attain high powers and larger image scales. Often, the ED Barlow is just a triplet lens which as far as I can tell, offers no real advantage visually over a SW 2X delux barlow. I use the latter in my Tak fluorite and it is completely free of residual CA even at very high power on the brightest objects. Comparing the SW Delux with my 2X Ultima barlow and 2X Takahashi barlow, I can see no observable difference in levels of CA or in image quality between the three. 

 

[Ruud]

I too prefer 1.25"  because I only use Barlows to get high magnifications from medium focal length eyepieces.

ED is not so important, but size is. Long Barlows require less steeply curved lenses, which benefits the image quality. Also, short Barlows have a higher chance of vignetting longer focal length eyepieces.

I have four Barlows: 1.8x and 2.5x older models, and 2x and 3x new models, all TeleVue. They're all fine, like so many others.
The point of having four is none, but I have plenty different magnifications to choose between and that is nice.

[Ricochet]

1 hour ago, emadmoussa said:

I'm aware more glass reduces light transmission, but how much on average?

Many short focal length eyepieces effectively contain a barlow in the nose piece. If the short focal length eyepiece has more elements than the longer one then there won't be much difference between that and the barlowed eyepiece in terms of glass losses. 

However, I would not buy a 2" barlow. 2" eyepieces are heavy enough without adding a 2" barlow to the equation. 

35 minutes ago, michael.h.f.wilkinson said:

I personally prefer using different EPs on planets , rather than faffing around with a Barlow (or even the better tele-centrics, like TV PowerMates, or Meade TeleXtenders I have for imaging). My planetary EPs are all par-focal, or have been made so with a suitable ring, and that means that I do not have to refocus when switching magnification, e.g. due to changes in seeing. With a Barlow or tele-centric I need to refocus a lot, which takes up valuable observing time. Of course, the luxury of having a range of planetary EPs comes at a cost, and a Barlow does add flexibility

If you structure your eyepiece collection so that all of your "short" focal lengths are obtained by barlowing longer eyepieces then there is only one step up/down where a focus change is required. On the other hand, if you use a barlow to try to fill the gaps between eyepieces I think refocusing becomes an issue. 

[domstar]

I'm not a fan of Barlows because it's one more fiddly thing to fiddle with, drop, get fingerprints on and leave my fingers numb. If I want to stay on the moon for a good deal of time without swapping around, I might, but where do you put all the caps? and the bottom lens is really exposed. In winter it's far too cold for them anyway.

I thought they'd really appeal because of their good value and the fact I usually love fiddling and being active but alas they're not for me.

[John]

I tend to be moving back towards not using barlows / telextenders but more to reduce faffing about with another item in the dark than optical degredation. The two Powermates I've been using dont seem to degrade the image at all but they are another, and rather expensive, piece of kit to fiddle around with so I'm not using them much. The resulting "stack" sticking out of the drawtube can be quite awkward as well.

The exception to the above is with the 7.2-21.5 zoom which I use with the Baader 2.25x Q Barlow as a high power zoom and it works really well. I tend to think of the zoom-barlow as a single unit though and rarely use them apart.

There are some formulae somewhere where you can calculate the impact that additional glass elements have on transmission (particular the glass-air boundaries) but with modern glass and coatings the figure is very low I think. I've had some fantastic planetary and lunar views with an Ethos+Powermate combination and thats around 13 lens elements and even more glass-air surfaces !

[michael.h.f.wilkinson]

Before I had an extensive EP collection, I did use one or two Barlows, including some cheap ones which really degrade image quality. All Barlow designs (whether singlet, doublet or triplet negative lenses) increase eye relief, and can cause vignetting in wide-field EPs. However, the tele-centric design (usually one negative and one positive doublet design) used in TV PowerMates, Meade TeleXtenders, Bresser SA-Barlows, and ES Tele Extenders is such that I do not really see the difference in quality between a Meade 14mm with 2x TeleXtender or at its native focal length. There is no change in eye relief, and I see no vignetting. The image does get 4x dimmer in terms of surface brightness, simply due to the increased magnification. Even a few percent loss in transmission pales in comparison.

[Rob]

I've always been a huge Barlow fan. However it MUST be of good quality.

I have had my Orion Shorty Plus APO barlow for 20 years now. It marries up with (what seems) to be every EP I've ever used. This Barlow is an original Japan edition also I will add, and you don't see them pop up very often now, just the Chinese remakes (not tried these to be fair). I also have a 2.5x GSO ED Barlow which again is of super quality, and seems to love the Meade 5000 series EP's.

The Antares 3x Japan Barlow I own is an Achromatic, but punches so well.  I purchased this one 12 ish years ago while experimenting with Planet imaging with webcams!. Works well with the EPs too

Rob

[emadmoussa]

23 minutes ago, John said:

 

The exception to the above is with the 7.2-21.5 zoom which I use with the Baader 2.25x Q Barlow as a high power zoom and it works really well. I tend to think of the zoom-barlow as a single unit though and rarely use them apart.

 

1

Curious, how did you find the 7.2 - 21.5 zoom? Planning on getting a Hyperion Zoom, which I'm quite familiar with, for the 100ED. But was also wondering if the 'cheaper' Skywatcher option is as good or close - minus the narrower field of view, of course. 

[John]

5 minutes ago, emadmoussa said:

Curious, how did you find the 7.2 - 21.5 zoom? Planning on getting a Hyperion Zoom, which I'm quite familiar with, for the 100ED. But was also wondering if the 'cheaper' Skywatcher option is as good or close - minus the narrower field of view, of course. 

I've posted in more detail here:

The narrow AFoV at the longer focal lengths is still there of course but as a trade off for very good, and instantly variable, high power performance, I can live with it a lot of the time.

The Hyperion zoom is a very good one as well and it has a dedicated barlow available too.

 

[JTEC]

As long as the Barlow is of decent quality, I don’t think there’s any need these days to worry about damaging the image. As for introducing extra glass into the train, with modern coatings etc, that’s also, imv, no longer something to worry about. If it was, superb, multi-element eyepieces like the Ethos would also be problematic. Which they’re not ... apart from the price.

I use a x2 2” Powermate - it has a supplied, rock solid 1.25 adapter, btw, so is equally useful for either fitting. In a rare gap in the more or less perpetual cloud we have ‘darn Sarf’ these days, I was experimenting with a 6mm Tak ortho, a newly acquired Vixen HR 3.4 (of which more anon) and a 10mm monocentric. I tried them all with the Powermate on a TEC140. If there was any image degradation over and above the difference you’d expect to see with an un-Barlowed equivalent focal length, I honestly couldn't see it.  

So, I think you might find a decent Barlow new or s/h a good choice - others are better placed to suggest which ones fall within your budget and deliver the quality.  As a paid up member of the minimum glass brigade, I used to resist using Barlows out of concern over possible image degradation, but I’ve learned that with a halfway-decent, modern example there’s no need to - quite the opposite in fact: a good Barlow is a really useful thing to have.

 

 

 

[Charic]

The poor old Barlow get its from both angles, some say  it reduces image quality, more glass in the optical train ( look at Tele vue's glass arrangement in some of their eyepieces, they have a Barlow) and  Barlowing also maintains eye-relief ( something I need to re-learn) as twice here its been mentioned there's an increase, and that a Barlow can double any eyepiece collection by the sum of the Barlow?

I have two Barlow eyepieces, SW Deluxe and Mead #140, both ok, but the Meade #140 is reputably better! though Ive hardly used them in their entirety at 2x, favouring to remove just the cell and attach that directly to the eyepiece for a reduced power.

That said, having sold off most of my 'better' eyepieces in favour of the BST's a Barlow could further help expand my collection, but unfortunately, any eyepiece lower than 12mm is going to start exceeding what my scope is capable of for practical reasons.

I might go ahead and permanently mount the SW cell to a 12mm BST, just to save time and provide with 200x which I don't have at present from the brand,  and just keep the #140 for the time I may need/want to Barlow another EP.

Emad........did'nt you just sell a #140?

[rwilkey]

Hi Emad, I would go for eyepieces and forget the Barlow, esp. a 2" one, 2" eyepieces are usually for widefield low power and using a Barlow defeats the object of getting a widefield eyepiece in the first place.  I made the mistake of getting one once, but soon sold it on, it just doesn't work.

[Louis D]

2 hours ago, rwilkey said:

Hi Emad, I would go for eyepieces and forget the Barlow, esp. a 2" one, 2" eyepieces are usually for widefield low power and using a Barlow defeats the object of getting a widefield eyepiece in the first place.  I made the mistake of getting one once, but soon sold it on, it just doesn't work.

If you were to get a 2" barlow, make sure to get a telecentric design or you will have all sorts of issues with long focal length, widest field of view eyepieces.  I sometimes leave my GSO 2x ED 2" barlow with a TV Panoptic Barlow Interface in the focuser and just try all sorts of eyepieces in it just to change things up and to see what works well with it.  Remember, not all 2" eyepiece are low power.  There are at the ES-92 and ES-120 series, among others, which are 2" only, but definitely not lowest power.  Having a good 2" magnifier allows them to be used at higher powers unavailable in a separate eyepiece.