johnnyha
Postmaster
Reged: 11/12/06
Loc: Sherman Oaks, CA
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Re: What size barlow or Powermate do you use
[Re: russell23]
#5637555 - 01/22/13 07:00 PM
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Dave, the 28mm ES 68 is a 2" eyepiece, I'm trying to figure out how you are using it with a 1.25" to 2" adapter? 
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russell23
Post Laureate
Reged: 05/31/09
Loc: Upstate NY
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Re: What size barlow or Powermate do you use
[Re: johnnyha]
#5637590 - 01/22/13 07:25 PM
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Dave, the 28mm ES 68 is a 2" eyepiece, I'm trying to figure out how you are using it with a 1.25" to 2" adapter?
The 1.25" to 2" adapter is a blue fireball adapter you can get from agenaastro:
http://agenaastro.com/blue-fireball-1-25-2-eyepiece-adapter.html
The barrel end of the adapter can drop into a 1.25" barlow and then the 28mm ES68 slides into the top of the adapter.
I just checked it with the 1.25" Dakin barlow and there was some very slight vignetting of the 28mm ES68.
Dave
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johnnyha
Postmaster
Reged: 11/12/06
Loc: Sherman Oaks, CA
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Re: What size barlow or Powermate do you use
[Re: russell23]
#5637597 - 01/22/13 07:30 PM
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Ah OK thanks Dave. Very strange looking beast!
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Scanning4Comets
Markus
Reged: 12/26/04
Loc: Hamilton, Ontario, Canada
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Re: What size barlow or Powermate do you use
[Re: johnnyha]
#5637601 - 01/22/13 07:33 PM
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Actually, the Meade 2" 28mm SWA vignettes quite a lot in a 2" barlow. In that adapter, the 2" 28mm ES or ANY 2" 28mm EP will vignette like crazy in that adapter Dave.
Cheers,
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russell23
Post Laureate
Reged: 05/31/09
Loc: Upstate NY
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Re: What size barlow or Powermate do you use
[Re: Scanning4Comets]
#5637753 - 01/22/13 09:00 PM
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Actually, the Meade 2" 28mm SWA vignettes quite a lot in a 2" barlow. In that adapter, the 2" 28mm ES or ANY 2" 28mm EP will vignette like crazy in that adapter Dave.
Cheers,
Mark,
I just came in from checking for vignetting with 28mm ES68. Unfortunately, the only 2" barlow I have is a 2.4x 2" Dakin barlow which must be placed before the star diagonal to reach focus. I saw no vignetting of the 28mm ES68 with the 2" Dakin barlow.
Using the 1.25" to 2" adapter with the 1.25" Dakin barlow there was some very mild vignetting. I could see the field stop and it was not quite as sharp as unbarlowed and there was a VERY slight uneven fading of the light close to the field stop. Unless you look for the vignetting you won't even notice it. It is so mild I wasn't even sure I was seeing vignetting at first.
Keep in mind that the field stop of the 24mm ES68 is 27mm and the field stop of the 28mm ES68 is ~31mm. I've found that these 2" eyepieces that have slightly larger field stops than the maximimum 1.25" field stop do not show significant vignetting when you use them with a regular 1.25" barlow and a 1.25" to 2" adapter that is placed into the barlow. The adapter elevates the 2" eyepiece farther from the barlow and apparently reduces the vignetting in the process.
With the 1.25" 2.5x powermate there is significant vignetting with the 28mm ES68 and there is not even a hint of the field stop detectable.
Dave
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Scanning4Comets
Markus
Reged: 12/26/04
Loc: Hamilton, Ontario, Canada
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Re: What size barlow or Powermate do you use
[Re: russell23]
#5637769 - 01/22/13 09:07 PM
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I was referring to using it in a Newtonian. Yours was used with a diagonal and it was "before" the diagonal, which would be why you don't see vignetting as the light path from the barlow is longer. 
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NeilMac
Carpal Tunnel
Reged: 09/25/10
Loc: MedHat, AB, Canada
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Re: What size barlow or Powermate do you use
[Re: russell23]
#5638778 - 01/23/13 11:54 AM
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1.25 TV 3X Barlow
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BillP
Postmaster
Reged: 11/26/06
Loc: Vienna, VA
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Re: What size barlow or Powermate do you use
[Re: Lance1234]
#5638979 - 01/23/13 01:54 PM
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I have four 1.25" Barlows and one 2" Telecentric (i.e., Powermate-like). The 2" is 4x. I have it in 2" Telecentric vs Barlow for a few reasons:
1 - To be able to get long focal length eyepices to high magnifications to take advantage of their typically more comfortable eye relief and larger eye lenses
2 - Wanted Telecentric design so eye relief does not get extended too much as this makes already long eye relief long focal length eyepieces more prone to blackouts. Also, some wide fields (and TV Plossls) need a telecentric so they won't vignette.
3 - Wanted 2" so I could insert a 1.25"-to-2" Helical focusing insert ( e.g., like this ) so could do fine focusing of the 1.25" eyepiece used (some scopes I have only have a 1-speed focuser).
Edited by BillP (01/23/13 01:55 PM)
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Knygathin
member
Reged: 12/31/09
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Re: What size barlow or Powermate do you use
[Re: BillP]
#5652783 - 01/30/13 05:05 PM
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If I put a 13mm Nagler on a Tele Vue Powermate or Barlow, (2x or 2.5x), will these added elements lessen the quality of what I see through the Nagler? Would it have been better to buy another Nagler instead, with shorter focal length approximately corresponding to the same increased magnification?
Which is best of Tele Vue Powermate and Barlow?
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NeilMac
Carpal Tunnel
Reged: 09/25/10
Loc: MedHat, AB, Canada
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Re: What size barlow or Powermate do you use
[Re: Knygathin]
#5654157 - 01/31/13 11:36 AM
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tv Barlow
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!
For astro-imagers, the above chart indicates the magnification for each Barlow (2x, 2x Big & 3x) as a function of distance from
the Barlow top surface to the imaging surface (CCD or film).
Edited by NeilMac (01/31/13 11:37 AM)
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khoferer
super member
Reged: 11/03/04
Loc: Mansfield, PA
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Re: What size barlow or Powermate do you use
[Re: NeilMac]
#5654856 - 01/31/13 06:32 PM
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I use the same UO "Wide View 3x" model that I've had for years. Never felt the need to change, I guess.
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2591
super member
Reged: 03/21/09
Loc: Queensland Australia
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Re: What size barlow or Powermate do you use
[Re: khoferer]
#5654926 - 01/31/13 07:28 PM
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most 1.25 barlows do not have internal baffeling, so when observing the moon you can get reflected light of internal surfaces on the field lens if your eyepiece robbing contrast. A two inch barlow does not have this problem as the internal walls are wide enough not to have this problem.
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photiost
super member
Reged: 12/14/06
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Re: What size barlow or Powermate do you use
[Re: 2591]
#5656686 - 02/01/13 04:27 PM
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I have a 2" focuser on my Reflector so I use a 2" Powermate.
When I use my older SPC102 Refractor it has a 1.25in focuser so I also have a 2x Ultima and 2.8x Klee barlow for use with that.
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mustgobigger
Post Laureate
Reged: 06/12/07
Loc: Michigan
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Re: What size barlow or Powermate do you use
[Re: photiost]
#5656753 - 02/01/13 04:53 PM
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2" i use brandon and 1.25 i use celestron and edmunds.
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dickie
member
Reged: 12/13/07
Loc: Cape Cod,Mass.
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Re: What size barlow or Powermate do you use
[Re: mustgobigger]
#5656899 - 02/01/13 06:14 PM
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Had the 2.5x and 4x powermates which are now gone, retained the Celestron 2x Ultima and Antares 1.6 , felt the latter two presented the same guality of views that the Powermates did. I love to barlow, they provide maximum usage of minimal good eyepiece collections.
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photiost
super member
Reged: 12/14/06
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Re: What size barlow or Powermate do you use
[Re: dickie]
#5657094 - 02/01/13 08:36 PM
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Had the 2.5x and 4x powermates which are now gone, retained the Celestron 2x Ultima and Antares 1.6 , ...
Yup the 2x Ultima is a keeper 
.
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: What size barlow or Powermate do you use
[Re: Lance1234]
#5657629 - 02/02/13 06:44 AM
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Curious what size Powermates or barlows people use (1.25" or 2" or both); and if you use a 2", why?
I have several Barlows, all are 1.25 inch. I have a good selection of eyepieces that are well corrected in fast scopes and I don't wear glasses when observing so Barlowing a 2 inch eyepiece would only transform a heavy, bulky eyepiece into an even heavier, even bulkier eyepiece with shorter focal length. I hope David's friend has a 20mm Type 5 rather than a 20mm Type 2 Nagler... 
I use a Barlow when when I need focal lengths shorter than 3.5mm. This is mostly double star stuff. I do have an Celestron Ultima but I prefer the 2 element Celestron Shorty, it's simple and does the job I need it to do. There are advantages to the Telecentrics but not at short focal lengths.
Jon
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FirstSight
Postmaster
Reged: 12/26/05
Loc: Raleigh, NC
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Re: What size barlow or Powermate do you use
[Re: Jon Isaacs]
#5657889 - 02/02/13 10:46 AM
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2" 2x Powermate + 1.25" 2.5x Powermate. I mainly use these to reach sub-4mm focal-lengths (my shortest f.l. "native" eyepiece is 3.7mm).
However, once in every great while, when there's a full moon (literally) I'll have fun stacking the 2.5x into the 2x to go to insane magnifications with my 12" reflector (f.l. 1500mm) using a 5mmT6 Nagler. This creates an effective 1mm eyepiece yielding 1500x magnification and the sensation of looking through the window of a spacecraft orbiting the lunar surface from about 160 miles up. Yes, the view is softer than desirably acceptable for normal observing, yet more than amply good for the purpose at hand of indulging a fantasy thrill ride above the array of clearly discernable lunar craters, mountains, and lava plains as they pass underneath. The upside to the softness of detail is that internal eye floaters which would likely be annoyingly, perhaps prohibitively intrusive at such a tiny exit pupil (0.2mm) are no problem, and neither is the accompanying dimunition of light on an object so bright as the moon. Unfortunately, for a variety of reasons, this same trick doesn't work well enough to create an acceptable spacecraft "fly-by" look at Jupiter; it registers as little more than a blurry blip that whizzes through the FOV too quickly to catch whether any even gross detail is visible.
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