Recommended Barlow

[Slimstar]

Looking for my first barlow, what will be a good first barlow?

[kev100]

Hiya,

The first thing to think about is why you want a Barlow? When I had a 5 inch scope, I found that using a 9mm EP was pretty much the limit for magnification that the scope could use, so I wouldn't recommend using a Barlow with your 9mm. A 1.5x barlow with your 25mm would give you (effectively) a 16mm eyepiece, and a 2x barlow a 12.5mm eyepiece (the latter pretty close to the 9mm you already have). Instead of a Barlow, you could look at a decent 15-16mm ep to fill in the middle ground in your EP collection. Something like a 16mm, 68 degree MaxVision from Explore Scientific, or a 15mm BST.

If you're after a barlow so you can attach a camera to the scope, then the Revelation 2.5x would be a good (and reasonably priced) start.

Kev

[Alfian]

Agree with Kev all the way. There is a real (and understandable - we've probably all been there)  temptation to go for as much magnification as the scope will  take. In practice, at least for me on my 130EQ (F5), the most used EPa are the 15mm & 25mm - which give  the most satisfying views. 

Also agree with Rev 2.5 Barlow which is really good for the money.

[ronl]

The Revelation 2.5x is very good and works well with my BST's, but

I find I only use it observing the Moon, as Kev has said, it's best to build

up your eyepieces, this link will help you to decide what you need, and

gives you the price range, also helps you to understand about eyepieces.

http://www.swindonstargazers.com/beginners/eyepieces.htm. it's a very 

good site.

[AstroAdam]

+1 for the revelation 2.5x....

Much better quality than the 2x...

[LeeB]

I recently brought the revelation barlow 2.5 and as above its an amazing barlow, not just at the price but at alot more. Super value. I normally don't use a barlow often, but have found I now am using it more.

[Alfian]

I'm sure I've read a post somewhere where someone claims the Rev 2.5 is nearer to 2x . I keep meaning to test this out.

[ScottS]

I'm sure I've read a post somewhere where someone claims the Rev 2.5 is nearer to 2x . I keep meaning to test this out.

I've read this also. Not sure how much truth there is in it, but the Barlow works great for me and doubles as a good collimation tool (twinned with my laser obviously).

[John]

Quite a lot of astro products don't quite match their quoted specification when measured independantly. I believe the Revelation 2.5x barlow is closer to 2.2x as is the Celestron Ultima 2x barlow and it's clone the Orion Shorty Plus 2x barlow. The Baader 8-24 zoom is another such item - the quoted field of view is 68-50 degrees (depending on the focal length but it's been measured as 70-42 degrees.

On the barlows, the Revelation 2.5x (2.2x) is good for it's cost despite the specification variance.

[Ptarmigan]

Help ! Wot am I missing :-  ?

A barlow is, in essence, a negative lens. When inserted into the light cone from the primary it shifts the focal point outwards, ( in effect stretching the focal length of the system resulting in increased magnification for a given eyepiece focal length )

The amount by which it moves the focus outwards depends upon how far into the light cone the barlow is placed.

If it is just a few mm inside of original focal point then the new focal point will be just a few extra mm further out, ie. not a big change so not a big power of barlowing?

So as far as I can see the thing determining the power of the barlow is how far in front of the eyepiece the barlow is ??

Which in turn depends upon the nosepiece of the eyepiece and the effective focal plane of that eyepiece.

So it isnt really a xX of the barlow, it all depends upon the tube (long tube = more mag.between the barlow and the particular eyepiece

ie not really anything intrinsic to the barlow itself ?

Where did I go wrong ?

Yes, the more negative the barlow is the greater the relative magnification, but the absolute xSomething depends also upon the eyepiece and its mounting ??

argh ! Help ! my brain hurts !

[Donkeiller]

I have a Revelation Barlow and I must be unlucky because it is a duffer.

Introduces coma at higher, x150 mags, which makes it U.S. for planets and doubles. 

The Celestron Barlow I kept from their EP kit is MUCH better, optically (but not in build).

[SpaceWalker]

Baader Q 2.25x is an excellent Barlow. According to Bill Paolini works as a ~2.5x with most of eyepieces.

[Jim Steele]

I have a Tal Barlow which is pretty decent. I think I paid about £30 for it but I don't see them much these days

[Dave In Vermont]

When you said "first Barlow" - I was deciding whether to chime in. How about changing that to "Last Barlow?" I mean that if you get one, why not the (insert argument here) best one so you'll never need to upgrade?

I normally steer clear from recommending TeleVue to people asking about eyepieces. I do that as many other will do that already. After all they are excellent. But they also cost more than many people can afford and still eat food. However I will make an exception when we're talking about a Barlow. And the TeleVue Barlows are hands-down excellent. And price-wise, not really that much more than other. Especially if you shop around a bit before pulling the trigger.

What I look for in a Barlow is one that is as close to being invisible as possible. By this I mean that you are adding more glass in between your eye and the object you are viewing. And this often results in a dimming of the object, and diminishing the clarity. So the ideal Barlow would be one that does it's job without screaming "Here I am! Can you see me?!" And the TeleVue is very, very quiet. The TeleVue PowerMate, many have noted, is even quieter-still. So that is my suggestion. And then you'll have at least one piece of kit with those neat green letters & numbers on it!

Clear & Dark, Silent Skies,

Dave

[oldfruit]

If you really need a Barlow then Televue for me too. I have had others but the Televue out performs them hands down. They can be picked up for a reasonable price second hand.

[RT65CB-SWL]

Hi 'Slimstar'

You could try one of these: http://www.ebay.co.uk/itm/AC555-Magni-Max-1-6x-thread-on-Barlow-lens-for-photo-visual-use-/221310472031 I don't know whether they the seller will post to or what astro-dealers you have in Malaysia.

I use one from time to time with my equipment. Extra glass in the lightpath is less photons making the trip!

[DeepSkyBagger]

I have a TeleVue x3 Barlow, which I find to be a very useful piece of kit, and as Dave (above) says, it's just about invisible. I think it's my 'last Barlow'.

[Slimstar]

Agree with Kev all the way. There is a real (and understandable - we've probably all been there)  temptation to go for as much magnification as the scope will  take. In practice, at least for me on my 130EQ (F5), the most used EPa are the 15mm & 25mm - which give  the most satisfying views. 

Also agree with Rev 2.5 Barlow which is really good for the money.

Hiya,

The first thing to think about is why you want a Barlow? When I had a 5 inch scope, I found that using a 9mm EP was pretty much the limit for magnification that the scope could use, so I wouldn't recommend using a Barlow with your 9mm. A 1.5x barlow with your 25mm would give you (effectively) a 16mm eyepiece, and a 2x barlow a 12.5mm eyepiece (the latter pretty close to the 9mm you already have). Instead of a Barlow, you could look at a decent 15-16mm ep to fill in the middle ground in your EP collection. Something like a 16mm, 68 degree MaxVision from Explore Scientific, or a 15mm BST.

If you're after a barlow so you can attach a camera to the scope, then the Revelation 2.5x would be a good (and reasonably priced) start.

Kev

Hi, thanks for the advice. Isn't the maximum magnification for my 5inch scope about 260x? The 9mm is currently giving me a magnification of about 70x, I thought I still have a large room to play with? I just tht of getting a barlow for viewing of planets, currently the view on anything other than saturn and jupiter is very small.

[Slimstar]

Thanks for all the advice

[SpaceWalker]

Hi, thanks for the advice. Isn't the maximum magnification for my 5inch scope about 260x? The 9mm is currently giving me a magnification of about 70x, I thought I still have a large room to play with? I just tht of getting a barlow for viewing of planets, currently the view on anything other than saturn and jupiter is very small.

Theoretically speaking, yes, 2D (D - aperture diameter in mm) or 130x2=260x is the max magnification for your scope. And that's what vendors want you to think to get your money  . Practically speaking, no.  Usually the max magnification is limited by the quality of your scope optics and even stronger by atmospheric conditions. So, it's usually accepted that a scope max limit does not exceed 1.5D, that is 195x for your scope if the primary mirror of a good quality.  The limits imposed by unsteady atmosphere reduce it much more especially for high power observations like planetary. I guess your best bet would be ~130-150x. Saturn allows more magnification for a good image, Jupiter is more demanding. The only exception is the Moon. I guess, you'll be able to use on the Moon 200-250x easily. IMO, your 9mm eyepiece combined with the 2x Barlow should be a good combination. For Jupiter and Mars it would be also very useful to add some contrast boosting filter like the Baader Moon&Sky Glow etc. And also my advise. If you don't have app like Stellarium on your computer yet, just install it, it's free. Enter Stellarium,  provide your scope, eyepieces, Barlow info and you'll be able to simulate planetary views with your specific equipment. 

[bingevader]

A 2x barlow might be the way to go with your current eyepieces.

I find they come into their own at providing the higher magnifications.

They conserve the eye relief which can be a problem with the less expensive short focal length eyepieces.

I use mine a lot on the moon with my 8mm and 7mm eyepieces.

It also means I don't have to buy two more eyepieces.