Barlow lens

[Venus_is_my_friend]

Hi all,

I was just wondering if anyone has had any experience with cheap barlows against more expensive ones.

What are the differences? If any.

Neil

[JamesF]

You don't say what magnification or what size, so if we assume 2x-ish and 1.25"...

The Tal 2x barlow is very popular, but hard to get hold of these days. The GSO/Revelation 2x and 2.5x barlows aren't bad and aren't very expensive either. I use the 2.5x heavily for planetary imaging. If you go a bit more expensive there's the Celestron Ultima and the Orion Shorty Plus which are near enough identical and actually around 2.3x. Those are the ones I'm familiar with. I think they cover a price range of about £40 to £80 and they're generally pretty good. In the 250PX though I'd not be sure because of its fast optics. I tend to use barlows for imaging and try to pick up good quality second-hand eyepieces where I have gaps for visual use so I've not tried any of them in my 10" dob.

James

[PhobosPhil]

I'm also interest in answers to the OPs question.

I have a decent quality diagonal, and a cheaper one (though one is 2" and one is 1.25") and the difference is noticeable.

I also have a decent quality eye piece and a cheaper one (both 1.25" and 26mm). The difference between the two is immense, everything looks brighter and clearer.

However, I currently only have a cheaper 1.25" 2x Barlow. When used in between the decent diagonal and decent eye piece, to my eye, I don't think it degrades the view, but as the view has changed, I find it difficult to tell.

[JamesF]

I've never had a good word to say about the kit 2x Skywatcher barlow and I eventually removed the lenses and use it as an extension tube for imaging. I've had quite a downer on these since. Recently though it's started to appear that perhaps some of them are reasonable whilst others are awful and it's perhaps actually the variability of quality that's the problem. If you have a poor one then I think a reasonable mid-range model could well make a noticeable difference.

You do need to remember that you shouldn't push the magnification too far for the seeing otherwise the image will appear to degrade no matter how good the barlow.

James

[John]

.......However, I currently only have a cheaper 1.25" 2x Barlow. When used in between the decent diagonal and decent eye piece, to my eye, I don't think it degrades the view, but as the view has changed, I find it difficult to tell....

I guess you won't really be able to tell until you try the same thing with a good quality barlow lens.

A barlow lens adds 4 optical surfaces into the optical system. If they are not figured, polished, coated, mounted and baffled (to prevent light scatter) to a high standard, they will degrade the resulting image quality, I feel.

[E621Keith]

I have several balows and IMHO a mid range barlow give a much better image than a basic one.

Kit: SW barlow:

Lots of chromatic aberration, noticeable scatter, image is less sharp than an equivalent eyepiece. Significant change in focus position

Basic: GSO/Revealation barlow

Better bulid quality. CA still noticeable, image sharper than SW. Not much scatter. Still inferior to equivalent eyepiece. Significant change in focus position

Mid range: Meade Series 5000 TeleXtender/Bresser SA barlow

Compression ring fitting, CA not noticeable. Sharp image. Quality approach equivalent eyepiece. Almost parfocal

High end: Nikon Eic-16

Twist lock compression ring (although I don't like Nikon's implementation of the twist lock), no CA, sharp image. Almost parfocal. Image quality is very good and variation in the eyepiece have more effect than the barlow. (my balowed LVW13 is better than LVW8, but barlowed LVW8 wasn't as good as LVW5). (I did not compare this to S5K because the magnification is different (1.6x))

I guess you won't really be able to tell until you try the same thing with a good quality barlow lens.

A barlow lens adds 4 optical surfaces into the optical system. If they are not figured, polished, coated, mounted and baffled (to prevent light scatter) to a high standard, they will degrade the resulting image quality, I feel.

Quality barlows such as a Powermate have 4 elements and even more glass air interface.

[John]

......Quality barlows such as a Powermate have 4 elements and even more glass air interface.

I was referring to a standard barlow Keith. A Powermate is not a barlow as far as I'm aware although it performs a similar role. But does it better !

[E621Keith]

I was referring to a standard barlow Keith. A Powermate is not a barlow as far as I'm aware although it performs a similar role. But does it better !

That's a good point. You are right, strictly speaking the Powermate and Telextender aren't true Barlow, but the term 'barlow' has became a generic term for describing any optical devices placed between telescope and eyepiece for increasing magnification. I think most users and even some manufacturers think this way (e.g. Bresser SA Barlow is actually a 4 elements extender identical to the Meade S5k TeleXtender).

[Venus_is_my_friend]

Sorry to be dumb but how do the Powermate and Telextender differ to a traditional barlow?

A barlow lens adds 4 optical surfaces into the optical system. If they are not figured, polished, coated, mounted and baffled (to prevent light scatter) to a high standard, they will degrade the resulting image quality, I feel.

I guessed this would be the case, but didn't know how big the difference in viewing would be. It sounds like being cheap is good to start but eventually you should aim to buy more expensive EP's, Barlows, Filters etc.

[John]

The Powermates and TeleXtender's use a different arrangement of lenses than a barlow lens. They deliver the boost in magnification without affecting the eyepiece eye relief and focal point. Barlows increase the eye relief and tend to move the focal point, sometimes by enough to make it difficult to get the eyepiece to focus. Because they are more complex than barlow they cost more too, of course !

[E621Keith]

The biggest differences is simple barlow pushes the focal point a lot further out, which may cause problem on scopes with limited focuser travel (such as Newtonian). The focal point doesn't move much with an extender, and you only need to make minimal focus adjustment when you use one.

Apart from that it will come down to individual barlow. A Powermate is very good and very expensive but so is a Zeiss Abbe barlow or Astrophysics BARCON

EDIT: need to type faster next time

[Venus_is_my_friend]

If money was not an issue would you guys rather have an extender then?

[John]

If money was not an issue would you guys rather have an extender then?

The Powermate is the best optical device of this type I've ever used. It simply delivers the additional magnification and then "gets out of the way". I tried the Meade 2" 2x TeleXtender for a while and it was pretty good too although there was a little more light scatter that the Powermate and a few other minor signs that it was in the optical train.

On barlows, the Antares 1.6x 2" is probably the best I've used. You do get some additional inwards focus travel and a shift in eye relief but optically it was excellent, even with complex eyepieces such as the Ethos.

[E621Keith]

If money was not an issue would you guys rather have an extender then?

Yes, there is less refocusing involved and less fuss.

The Bresser SA barlow (an extender) is probably the cheapest extender on the market at the moment, it's just a bit more expensive than a TV barlow (a barlow) and 40% cheaper than a TV Powermate (an extender).

http://www.telescope...1.25-inch-.html

[Rustysplit]

Very interesting thread. I am in the market for a decent barlow/extender at the moment. I looked at the Bresser you mentioned Keith, Are they any good?

[E621Keith]

I have the Meade Series 5000 2x TeleXtender (same thing made by the same company). It performs very well, no false colour, very little change in focus position. It's better than SW or the GSO barlow, but that's expected for a barlow/extender costing several times more.

I haven't compared it to its competitors in the same price bracket so I can't comment. Alternatives includes the Televue 2x barlow and Celestron Ultima, both are well established barlow with a good reputation.