Does anybody no how close in performance these two barlows are? Is the powermate noticably better? I appreciate your feedback.
powermate vs televue 2x barlow
Started by matt elliott, 11/05/2002 10:41PM
Posted 11/05/2002 10:41PM
Opening Post
Posted 11/05/2002 11:23PM
#1
Hi Matt,
Those here with far more optical expertise than I will likely be able to give you better input, but FWIW I already own a 2X TV Big Barlow, but recently picked up some Powermates as well.
I'm fortunate to have a well-rounded selection of eyepieces and seldom found the need to use the barlow, but was seeking the best solutions for using an SLR with with my scopes... something that would not only to give me the image scales I wanted but would also preserve the image quality my scopes deliver.
After discussing the situation with "Uncle Al", I ordered a 2X and 4X Powermate (to replace my 2x Big Barlow) and T-adapters for each. The Powermates, as you are probably aware, are not simple barlows but telecentric* devices that provide a virtually distortion-free wide potential image scale when used alone or combined together.
Al ingeniously designed these with extenders that are removable from the chromed optics barrels, and (optional)customized T-adapters that can be screwed on in their place. This allows close placement of a camera or CCD (using a T-ring), to reduce or eliminate vignetting.
Lest you think the Powermates are only beneficial for persnickity imagers and such, let me state that they are also a great addition for visual use as well. They now sport captive brass clenching rings (ala AP style) to hold the EPs in place, and yes, I'd buy them again in a heartbeat!
*Before seeing the term in the TeleVue Powermate ads and speaking with Al, I had no idea at all what telecentricity was or how the lack of it could affect the image. This is an interesting essay on the subject and may help explain what the telecentric Powermates can do (that a normal barlow doesn't):
http://makeashorterlink.com/?L25562512
Paul
PS: The below image was taken using only a 2X Powermate (no eyepiece) via a Canon D60LSR and FS128 Tak' (processed with Images Plus and final finishing with Adobe PhotoShop).
Those here with far more optical expertise than I will likely be able to give you better input, but FWIW I already own a 2X TV Big Barlow, but recently picked up some Powermates as well.
I'm fortunate to have a well-rounded selection of eyepieces and seldom found the need to use the barlow, but was seeking the best solutions for using an SLR with with my scopes... something that would not only to give me the image scales I wanted but would also preserve the image quality my scopes deliver.
After discussing the situation with "Uncle Al", I ordered a 2X and 4X Powermate (to replace my 2x Big Barlow) and T-adapters for each. The Powermates, as you are probably aware, are not simple barlows but telecentric* devices that provide a virtually distortion-free wide potential image scale when used alone or combined together.
Al ingeniously designed these with extenders that are removable from the chromed optics barrels, and (optional)customized T-adapters that can be screwed on in their place. This allows close placement of a camera or CCD (using a T-ring), to reduce or eliminate vignetting.
Lest you think the Powermates are only beneficial for persnickity imagers and such, let me state that they are also a great addition for visual use as well. They now sport captive brass clenching rings (ala AP style) to hold the EPs in place, and yes, I'd buy them again in a heartbeat!
*Before seeing the term in the TeleVue Powermate ads and speaking with Al, I had no idea at all what telecentricity was or how the lack of it could affect the image. This is an interesting essay on the subject and may help explain what the telecentric Powermates can do (that a normal barlow doesn't):
http://makeashorterlink.com/?L25562512
Paul
PS: The below image was taken using only a 2X Powermate (no eyepiece) via a Canon D60LSR and FS128 Tak' (processed with Images Plus and final finishing with Adobe PhotoShop).
Attached Image:
Posted 11/06/2002 12:04AM
#2
Thomas Back talked about this recently in the TMB forum on egroups.
His list of favorites:
1. Zeiss 1.25" ED Barlow (very rare).
2. TeleVue Powermate 2.5x (highest Strehl ratio of any
Barlow tested -- 99.1%).
3. Astro-Physics 2" Barcon Barlow
4. Nikon 2x Barlow for their 100mm f/12 apochromat
His list of favorites:
1. Zeiss 1.25" ED Barlow (very rare).
2. TeleVue Powermate 2.5x (highest Strehl ratio of any
Barlow tested -- 99.1%).
3. Astro-Physics 2" Barcon Barlow
4. Nikon 2x Barlow for their 100mm f/12 apochromat
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