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barlow lenses vs powermates

ve1drg

By ve1drg
in Discussions - Eyepieces

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ve1drg

ve1drg

Posted
Posted

Wondering if there is any difference between powermates and barlow lenses?

I was told it is about the same ,  that there is no difference.

I always thought the barlow lenses were better.  They seemed to have better references.

But otherwise I have no knowledge on which might be the better.

I have a powermate now (2x).   And thought that if it was agreed that the barlow lenses were better than  i would give that a try.

Any thoughts please?

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catman161

catman161

Posted
Posted

OMG! Televue powermates in my opinion beat any Barlow lens hands down! Barlow lens decrease surface brightness and powermates do not. You just plonk the powermate in and it's as though it's not there (aside from the magnification!). You'd be the first person I've heard of swapping a powermate for a Barlow!

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John

John

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Powermates just add the extra magnification, nothing else. You would not even know they are there. The Explore Scientific Focal Extenders work in the same way and are excellent as well.

If you have a Powermate, you already have the best amplifier there is.

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AlexB67

AlexB67

Posted
Posted

The one benefit a barlow may give you if you have very short eye relief eyepieces, you can increase that eye relief using the barklow as well as magnifying the image, useful when wearing glasses for some eyepieces. Powermates will retain the eye relief of the eyepiece as is. 

Some barlows have the option of removing the lower element and can also be used as a lower magnifier. Typically the lower element will give 1.5x, and when the barlow is used in full it gives 2x.  AFAIK with the ES extender and powermates you will get the two times only, and also regardless where you place them in the train, they will always give that 2x afaik. 

Barlows can be a bit approximate too, an advertised  2x may give 2.3x or 1.7x in practice. I am not not convinced my skywatcher always gives 2x anyway, though I have never measured it.

As already said, stick with the powermate, though I don't own one, they are great from what I read by all accounts ! :smiley:

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Don Pensack

Don Pensack

Posted
Posted

Well, a barlow is a 2-element negative lens that adds magnification by expanding the image scale.  They have some disadvantages:

--they tend to lengthen the eye relief of an eyepiece, which could be a problem with long focal length eyepieces.

--their magnification is only accurate at the correct distance from the lens.  Closer, they provide less power; farther they provide more.

This could be an advantage if you like the idea of a sliding magnification by merely changing the eyepiece-barlow distance.

--they widen the field and can result in vignetting in eyepieces if part of the outer field misses the lenses in the eyepiece.

--they require 1/2" to 3/4" additional in-travel of the focuser.

A PowerMate, which follows the 2-element negative lens with a two element positive lens:

--doesn't affect the eye relief of the eyepiece

--the magnification doesn't change more than a tiny bit with distance from the lens

--doesn't vignette the eyepiece's field of view

--if the eyepiece's focal plane is at the shoulder of the eyepiece where it sits, no in-travel of the focuser is necessary.  If the focal plane differs

from that location, some in-or-out travel will be necessary, but not as much as a standard barlow.

Other companies make telecentric barlows: Explore Scientific, Harry Siebert, but I don't believe they made any attempt to make them par-focal

with the eyepieces.

Don Pensack

Los Angeles

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davefrance

davefrance

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Not sure about other manufacturers but with TV Powermate you can unscrew the black part from the silver lens holder and add a TV adaptor to accommodate T42 camera ring. I use this a lot for both day(nature) and night(astro) photography, Gives a great boost to magnification. 

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RikM

RikM

Posted
Posted

--they require 1/2" to 3/4" additional in-travel of the focuser.

That is interesting Don. I find with my 2.5x Televue barlow that the focal point is shifted out  about a half an inch. Or did I misunderstand what you wrote? I use a 10" f/4.7 Newtonian and Pentax XW's predominantly.

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denis0007dl

denis0007dl

Posted
Posted

I have all Powermates, and all best worlds barlows like Zess barlow, TMB barlow and APM 2.7x barlow and

AP BARADV.

I made lots of tests, and in my experience, these worldbest barlows are unbeatable by any Powermate!

These barlows are simply superb especially first three mentioned.

APM barlow is in my opinion too low in price, so grab it, you will never regret!

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rory

rory

Posted
Posted

I have all Powermates, and all best worlds barlows like Zess barlow, TMB barlow and APM 2.7x barlow and

AP BARADV.

I made lots of tests, and in my experience, these worldbest barlows are unbeatable by any Powermate!

These barlows are simply superb especially first three mentioned.

APM barlow is in my opinion too low in price, so grab it, you will never regret!

Oow, one going against the grain here then . Interesting . I've never read anyone putting a Barlow over a power mate before now.

I've not heard of the "apm " . Any more info on that ?

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denis0007dl

denis0007dl

Posted
Posted

Indeed sounds interesting  did a quick google on the APM, Is it one of the ones I wonder ?

http://www.apm-telescopes.co.uk/apm-coma-barlow.html

but it also serves as a coma corrector it seems.  Denis do you say that because it is also a coma corrector or because of some other reason ?

edit: oops beat me to the link, sorry  :)

AlexB67, on 06 Mar 2014 - 8:27 PM, said:

Indeed sounds interesting  did a quick google on the APM, Is it one of the ones I wonder ?

http://www.apm-telescopes.co.uk/apm-coma-barlow.html

but it also serves as a coma corrector it seems.  Denis do you say that because it is also a coma corrector or because of some other reason ?

edit: oops beat me to the link, sorry 

This barlow have so chrystal clear image that you cant beleive, very pinpoint stars, tottal neutral, cool tone images, it is in same lueage with my Zeiss and TMB barlows, plus it give you coma corrected field even on poor corrected eyepieces on fast scopes.

Mechanics is also great, and 1.25" adaptation is best of all because it position eyepiece exactly in center.

Great job from APM.

Barlow have 2 cemented lenses.

I like also Powermates, but comparing Powermates with these ultimate barlows, in very clear nights,

with good eyes, I can easily detect that Powermates produce very slightly warm tint on objects,

but very slight, and also, picture is little brighter on these barlows than Powermates,

probably because law of physics-4 elements in PMs vs 2 elements in barlows.

But also do not forget that PMs have 4 air-to-glass surfaces, while barlows have only 2,

and these means less scattered light.

But remember that I test these ultimate very expensive barlows(except APM and AP barlows which are

not so expensive)

plus it 

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denis0007dl

denis0007dl

Posted
Posted

One more time, to comment which is better optically, ultimate barlows like these or Powermates,

you must have good eyes, great sky, good or even better scope, and of course all them in same 

place in same time, otherwise you can just presume.

I made many tests with my two friends on fast newts and 6" f/8 refractor, and all we see same, these barlows give more neutral tone

images than PMs, little more pinpoint stars, and visible more brighter images!

They cant be beated with PMs without doubt!

...but this was our result!

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rory

rory

Posted
Posted

Interesting Denis, seems you've done quite abit of comparing . Do you use them for imaging too or visual only ?

Sorry scrap that , I see the word images in the last post. :-/

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