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Televue Barlows and Powermates

 
   

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Concept: While Barlows are powerful tools, the negative element defining them also limits their ability. The simple negative element Barlow increases eyepiece eye-relief. With short focal length eyepieces the effect is negligible. However, on long focal length eyepieces the exit pupil position moves well beyond the designer's intended position, resulting in vignetting with many eyepieces. This is why "Shorty" Barlows in particular, with their strong negative element often vignette and degrade long focus eyepieces. My 4-element form picks up where the Barlow concept can go no further. Powermate™ is a technically universal solution, using a positive field lens to redirect field rays. The result is an exit pupil that stays where the eyepiece designer intended. With freedom from aberrations, greater magnification potential, and compact size, I hope you'll agree Powermate™ raises the standard for image amplification. — Al Nagler

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4x Powermate™ shown for illustration. All 2" models include 1¼" adapters (left). Standard Eyepiece Adapter (middle-top) is removable to allow Photo/Visual assembly (right) to use optional T-Ring Adapters (middle-bottom) for imaging.
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4x Powermate™ photo setup with T-Ring adapter (left).
4x Powermate™ visual setup with 1¼" adapter (right).

Al Nagler's 4-element concept, continues the tradition of full-field sharpness with optimum aberration control. Like long eye-relief? Retain the eye-relief of long focal length eyepieces, while at high power. Enjoy, for example, the sharpness and comfort of the 32mm Plössl at up to 5 times the power!

Powermate™ vs. Barlow

To understand the Powermate™, we must first understand the Barlow lens. Barlows amplify the power of a telescope. They can be considered "focal reducers" for eyepieces, or "focal extenders" for objectives. Terence Dickenson, in his Barlow test report in Sky and Telescope, July 1997, says: "Technology has erased the old objections. A modern Barlow will not degrade your telescope's optics. Anyone telling you otherwise is using outdated information. Moreover, the highly regarded Nagler eyepieces and their clones have built-in Barlows, ample evidence that the lens is not some detrimental intruder." Thanks, Terence, for laying the myth of the degrading Barlow to rest.

A high quality Barlow must be properly designed and manufactured in order to avoid compromising a telescope's color and spherical aberration corrections. The "invisibility" of Tele Vue's 2-element Barlows has been noted in test reports in the astronomy magazines. However, by the nature of its negative power lens, a Barlow will do more than just increase magnification, regardless of the number of elements.

The diverging rays leaving the Barlow result in moving the exit pupil further out, thereby extending the eye relief. In short to medium focal length eyepieces the change is not noticeable. However, in the case of long focal length eyepieces, the increase can be significant and not without performance consequences.

Vignetting can occur due to the altered ray path, when the eyepiece's lenses are not large enough in diameter to allow all the rays to make it through. Shorter Barlows, or ones with too much magnification, only exacerbate the problem because the ray path entering the eyepiece is steeper.

We had to go beyond the Barlow concept to achieve the goal of a compact, high power, fully corrected image amplifier. The Powermate™ consists of a negative doublet plus a positive "pupil-correcting" doublet. This 4-element system provides the magnifying function of a Barlow without its limitations by restoring the field rays back to their original direction, as if the Powermate™ were not there. The result is a pure magnification increase.

Barlows
TeleVue.com: Eyepiece Accessories > Barlows > Background

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Concept: I originally designed the Tele Vue Barlow line to complement the high performance of our eyepieces. Only 2 elements of high index glass were required to reduce all aberrations to well below the airy disc in an f/4 system. It has taken a good 15 years, but I think we're finally laying to rest the popular myth of the "degrading Barlow." In a 1997 Sky & Telescope review, Terrence Dickenson wrote "...Technology has erased the old objections. A modern Barlow will not degrade your telescope's optics. Anyone telling you otherwise is using outdated information. Moreover, the highly regarded Nagler eyepieces and their clones have built-in Barlows - ample evidence that the lens is not some detrimental intruder." Thanks Terry, I couldn't agree more. — Al Nagler

Properly designed Barlows do wonderful things: They amplify power, slow the telescope's f/# (improving eyepiece sharpness), and give designers the opportunity to compensate for eyepiece aberrations.

Tele Vue Barlows use multi-coated high index glasses for optimum aberration correction, exceptional contrast with virtually no light loss. Observed performance is aberration free, even when tested with f/4 scopes. They even improve our competitor's eyepieces and telescopes!

Tele Vue Quality

Compromise image quality in any part of the optical chain and you've compromised every part! Tele Vue product design and execution deliver consummate satisfaction. Every Tele Vue Barlow must pass the same rigorous f/4, full field testing as all our eyepieces. All Tele Vue Barlows now use brass clamp rings for secure, non marring holding of eyepieces and accessories.

1¼"Barlows

Offered in 2x and 3x magnifications, these 1¼" Barlows perform identically. Simply choose either or both based on your eyepiece collection. Features include parfocal-ization, 1¼" filter threads, captive lock screws that won't fall out and full multicoatings.

2" Big Barlow

Offered in a 2x magnification, the Big Barlow is ideal for Newtonian scope owners. It will be parfocal with both 2" and 1¼" eyepieces in this application. Features include 1¼" eyepiece adapter, threads for 48mm filters, captive lock screw and full multi-coatings.

Note: The Big Barlow is not recommended for use with 2" diagonals because it's length prevents it from being parfocal. With some telescopes, focus might not be reached, particularly when the interface lens is also used with it. A far better approach with no potential problems in any scope or with any eyepieces is to use the 2" 2x Powermate (PMT-2200), which essentially includes the Pan-Barlow Interface

 

 

 

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Televue 2X Powermate - 2"

* Televue Power Mate 2X Image Amplifier PMT-2200 accepts all 2" eyepieces and accessories and comes with additional 1.25" adapter! * Incorporates a "positive" and "negative" doublet for better optical correction. * Higher magnifications are possible with high optical performance compared to "doubling up" Barlows. * Televue Power Mate 2X Image Amplifier PMT-2200 delivers high performance for CCD or film! * Accepts Televue's T-Ring Adapter (PTR-4201) for close coupling to cameras and CCD imagers. * Ideal for Hydrogen-alpha filter use such as with Daystar models.


Our price: $310.00 (€269.70)
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Televue 2X Powermate T-Ring Adapter - 2"

* The TeleVue T-Ring PowerMate Adapter PTR-2200 was designed for the 2" TeleVue 2X Powermate Barlow lens. * It replaces the eyepiece holder, presenting T-ring threads for photography. * The TeleVue T-Ring PowerMate Adapter PTR-2200 is machine threaded a fully blackened for maximum contrast.


Our price: $57.00 (€49.59)
Market price: $70.00 , save 19%
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Televue 2.5X Powermate - 1.25"

* Televue Power Mate Image Amplifier - PMT-2513 accepts all 1.25" eyepieces and accessories. * Incorporates a "positive" and "negative" doublet for better optical correction. * Higher magnifications are possible with high optical performance compared to "doubling up" Barlows. * Televue Power Mate Image Amplifier - PMT-2513 delivers high performance for CCD or film! * Accepts Televue's T-Ring Adapter (PTR-1250) for close coupling to cameras and CCD imagers. * Ideal for Hydrogen-alpha filter use such as with Daystar models.


Our price: $205.00 (€178.35)
Market price: $260.00 , save 21%
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Televue 5X Powermate - 1.25"

* Televue 5X PowerMate is a must for eyeglass wearers! * Televue PMT-5126 works with all 1.25" eyepieces and diagonals. * Fully multi-coated, with blackened lens edges and internal anti-reflection threading. * The Televue 5X PowerMate is ideal for long focus CCD and film photography. * Delivers stunning high magnification with no vignetting or image degradation.


Our price: $205.00 (€178.35)
Market price: $310.00 , save 34%
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Televue Powermate T-Ring Adapter - 1.25"

* Televue T-Ring Adapter - PTR-1250 replaces the eyepiece holder on the 1.25" 2.5x and 5x Televue Powermate Barlows. * Threads directly onto the chrome barrel in place of the eyepiece holder. * TeleVue T-Ring Adapter - PTR-1250 is suited for photography with short focal length refractors capable of using 1.25" visual accessories. * Allows for the attachment of a CCD camera.


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Televue 4X Powermate - 2"

* Televue Power Mate 4X Image Amplifier PMT-4201 accepts all 2" eyepieces and accessories and comes with an additional 1.25" adapter! * Incorporates a "positive" and "negative" doublet for better optical correction. * Higher magnifications are possible with high optical performance compared to "doubling up" Barlows. * Televue Power Mate 4X Image Amplifier PMT-4201 delivers high performance for CCD or film! * Accepts Televue's T-Ring Adapter (PTR-4201) for close coupling to cameras and CCD imagers. * Ideal for Hydrogen-alpha filter use such as with Daystar models.


Our price: $320.00 (€278.40)
Market price: $415.00 , save 23%
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Televue 4X Powermate T-Ring Adapter - 2"

* The TeleVue T-Ring PowerMate Adapter PTR-4201 was designed for the 2" TeleVue 4X Powermate Barlow lens. * It replaces the eyepiece holder, presenting T-ring threads for photography. * The TeleVue T-Ring PowerMate Adapter PTR-4201 is machine threaded a fully blackend for maximum contrast.


Our price: $57.00 (€49.59)
Market price: $70.00 , save 19%
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Televue 2X Barlow - 1.25"

* Televue Barlow Lens - BLW-2125 uses only multi-coated high-index optical glass. * Superior contrast and exceptional light transmission. * Televue Barlow Lens - BLW-2125 offers 2X magnifying power. * Accepts all 1.25" focusers, diagonals, eyepieces and accessories.


Our price: $120.00 (€104.40)
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Televue 3X Barlow - 1.25"

* The Televue 3X Barlow Lens - BLW-3125 uses only multi-coated high-index optical glass. * Superior contrast and exceptional light transmission. * Televue Barlow Lens - BLW-3125 offers 3X magnifying power! * Accepts all 1.25" focusers, diagonals, eyepieces and accessories. * Weighs 7 ounces and measures 5" in length.


Our price: $120.00 (€104.40)
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Televue Big Barlow 2X - 2"

* The Televue 3X Barlow Lens - BLW-3125 uses only multi-coated high-index optical glass. * Superior contrast and exceptional light transmission. * Televue Barlow Lens - BLW-3125 offers 3X magnifying power! * Accepts all 1.25" focusers, diagonals, eyepieces and accessories. * Weighs 7 ounces and measures 5" in length.


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