A good 2X Barlow

[george7378]

I have been using my standard Sky-Watcher 2X Barlow for a while now, but there is a very notable drop in image quality when I put it in. Can anyone please recommend a better one (or a good 5mm eyepiece)? Thanks.

[AndrewT]

I have noticed the same thing george with mine, the barlow i am going to get is a celestron ultima which from all reports is a good barlow

[brantuk]

A good step up from your supplied barlow is the Celestron Ultima 2x (equiv to the Orion Shorty 2x) or the Televue Barlows. Better still but more expensive is the Televue Powermate. A good budget barlow is the Tal 2x or 3x that FLO sell. Antares do a nice mid range 1.6x 2" model

[cgarry]

I have the Televue Powermate, and it is fantastic. Not cheap though.

[John]

A 5mm orthoscopic eyepiece will cost less than a decent barlow such as the Ultima. So that's another option as would be a 5mm TMB Planetary eyepiece (or one of it's clones). The TAL is the lowest cost decent barlow lens IMHO with the Ultima a step up again.

[inspectapart]

I also have a celestron ultima 2x which I bought on Ebay

I can`t see any downside or lack of contrast / brightness at all when using this barlow. It really is a good choice, especially if you can find one at a fair price.

bob

[riklaunim]

I was playing with RGB filters and 2x GSO Barlow (achro) and 2.8x UO Klee APO Barlow. The achro had a small focus shift although it performs very good (hard to tell if 2.0x APO would give more in the same imaging situation). Celestron Ultima, Vixen DeLuxe, AE or Antares APO Barlows should be good from the 2.0x. GSO makes APOs except only the 1,25" 2x (why?)

[Adrian Condon]

Hi,

If you are interested Roger B has a Celestron Ultima x2 Barlow for Sale on SGL for £68.

The alternative is a Big Barlow x2 or a Powermate x2 from Televue. Just watch your eyes water with the price!!!

The Big Barlow with a Reflector scope allows you to use 1.25" and 2" lens, definitely worth considering. An astro mate of mine has a Televue Big Barlow and he raves about the improvement in performance. Have a look at the Televue website, they have an article on Powermate vs Big Barlow.

Tele Vue Optics: Powermates

Before spending big money, ask yourself how often do you need to use a barlow?

Let us know what you what you have decided doing and how you rate the Wow factor.

Cheers

Adrian

[sixela]

Better still but more expensive is the Televue Powermate.

I have had both a Televue 2x and a 2.5x Powermate. Powermates arent "better" except if you care about the peculiar characteristics of telecentric telextenders:

-lack of vignetting in some eyepieces (TV Plössls at the extreme edge, some 22-24mm wide fields);

-no eye relief extension on long focal length eyepieces (like the 24mm Panoptic)

-constant magnification factor regardless of spacing between barlow and eyepiece or sensor (the reason many planetary imagers like them)

-small insertion depth (with many barlows, you have to insert them deeply in the focuser; if you don't, you need enough focuser in-travel to compensate).

But these are not always relevant, and optically, I actually prefer the "regular" TV barlows to the Powermates.

Yes, the TV barlow is a price/performance killer. I had slightly better barlows since (a 1.8x TMB barlow and the excellent Baader/Zeiss 2x, and a Baader VIP which is probably more or less equal in quality to a TV barlow and which I use as a screw-on barlow on some of my eyepieces), but they were all a lot more expensive and the difference between them and a TV is really small.

[sixela]

Hi,

If you are interested Roger B has a Celestron Ultima x2 Barlow for Sale on SGL for £68.

The alternative is a Big Barlow x2 or a Powermate x2 from Televue.

Uhm -- why just these? TeleVue also sells 1.25" barlows (and even Powermates), and they're a lot cheaper. To me, the 2" barlows really only make sense if you have very expensive eyepieces in 2" format that you don't want to buy once more (e.g. if you have 21mm and 17mm Ethe eyepieces, or a set of T4 Naglers - buying a barlow is a lot cheaper than buying two or three extra Naglers or Ethe!)

Otherwise, you tend to go from regular 2" eyepieces to longish 1.25" eyepieces and barlow only the latter to get to the high magnifications

Just to given an example, I go from 21mm Ethos straight to an unbarlowed 13mm Ethos most of the time, and occasionally to an unbarlowed 16T5 Nagler. So if you have eyepieces from that 16mm eyepiece downward, there's no need for a 2" barlow.

I do barlow my 21mm (effective focal length 10mm) and 13mm Ethos (effective focal length 8mm), but that's mainly because buying two more Ethe is really costly, and because I sometimes like to carry just the two Ethe plus the screw-on barlow to do most of my observations.

The Big Barlow with a Reflector scope allows you to use 1.25" and 2" lens, definitely worth considering.

But a Big Barlow plus a large 2" eyepiece is a lot more cumbersome (and more difficult to balance, if you have a Dob) than a 1.25" eyepiece. Unless you have quite a bit invested in that 2" eyepiece, it's les practical than, say, a 16-24mm 1.25" eyepiece.

[sixela]

I have been using my standard Sky-Watcher 2X Barlow for a while now, but there is a very notable drop in image quality when I put it in.

But the "drop in quality" might in fact be something inherently associated with the higher magnification. When you increase the magnification 2x:

-in bad or so-so seeing, the image will start to blur (or become unstable) if the magnification becomes too high;

-surface brightness of extended objects will decrease by a factor of 4x with a 2x barlow. Sometimes that will dim the views too much;

-if the exit pupil drops under 1mm (i.e. when the resulting magnification exceeds the millimetres of aperture of your scope), you'll start noticing the floaters in your eye a lot more.

If that's what you perceive as a "drop in quality" of the image, then not even the super-dooper Baader/Zeiss barlow will help. You're just pushing magnification too high, or you simply aren't used to coping with the drawbacks inherent to large magnifications (views will appear more mushy except in brief instants of good seing --but these will reveal a lot of detail when they happen--, you'll have to work harder to avoid looking through the floaters in your eye, etc.)

[russ]

I agree with sixela. If you are aiming for the equivalent of a 5mm eyepiece with the 250PX, then the noticeable drop in quality is most likely due to high magnification (240x) rather than the barlow. I have used the Skywatcher 2x Deluxe and it was not too shabby (my example at least). Certainly comparable to the slightly disappointing, again my two examples, Tal 2x barlow.

If you are considering the Ultima, why not buy the identical Orion Shorty Plus 2x? It costs less new than most people want secondhand for their Ultima's.

Also, the TV 2x barlow, like the TV Plossl, costs less than most people realise.

[part timer]

I've used a few barlows.

The two Tal 2x's were very sharp and distortion free but had a yellow colouring to the lenses that made high powers very dim.

The Tal 3x is optically perfect but has a tiny lens that vignettes longer focal length eyepieces.

I've now had the misfortune to own 3 skywatcher 'delux' barlows ( bought one and the others came as extra's with scopes). The first two were put in the bin after a few uses. The third was better but could only be used in longer focal ratio telescopes, certainly not at f5!

The televue 2x is great and will be great in all scopes.

I now use a Meade 140 apo 2x and it is just as good as the televue but costs about half as much!

The televue gave a slightly dimmer and 'warmer' vue. The meade gives slightly more light scatter but this is easy to control or 'fix'.

Both of these are longer barlows which will stick out of a stardiagonal and look a bit wierd but will work fine. This is not a issue in a Newt.

[sixela]

The Tal 3x is optically perfect but has a tiny lens that vignettes longer focal length eyepieces.

It's actually not the tiny lens (that's actually sized properly for any 1.25" eyepiece, at least unless you plan to use the barlow in a sub f/4 scope).

It's the short focal length that means that in some longer focal length eyepieces (and some aggressively baffled shorter ones) the light cones are displaced more towards the edge in the eyepiece and cause vignetting in the eyepiece.

The only way to avoid that is to use a longer focal length 3x barlow or to use a telecentric "barlow" (Powermates don't come in "3x" fashion, but the Meade 5000 TeleXtenders do).

Both of these are longer barlows which will stick out of a stardiagonal and look a bit wierd but will work fine.

If, of course, you have the proper amount of focuser in-travel left.

[RME1]

I use both the TV 2x, 3x barlows and a 2.5x powermate and find them all excellent.

Richard.

[george7378]

Thankyou very much for all the responses - I've bought a TMB 5mm planetary eyepiece instead - I will have to see how it stacks up.