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Equipment Discussions >> Equipment

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MaestroMyth
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Reged: 02/16/06

Loc: CT
Barlow vs. Powermate?
      #4774561 - 08/28/11 08:58 PM

Hi all,

Going to upgrade a 'free' Barlow that came with my scope.

I'm looking at the TV line and I don't understand the difference between their Barlow and Powermate. 2x, 3x, 4x, etc.

I use an 8 inch SCT for visual and astrophotography.

If not a TV offering, can anyone recommend a Barlow that would be an upgrade over my standard Parks Barlow?

Thanks in advance!


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ischua
Under the Radar
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Reged: 07/17/08

Loc: Below Snow Plop, N Y
Re: Barlow vs. Powermate? new [Re: MaestroMyth]
      #4774663 - 08/28/11 10:07 PM

A Powermate is a corrected barlow no aberrations.
You can unscrew the 2" eyepiece housing and screw on a T-ring adapter for attachment of CCD or camera


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Barlow vs. Powermate? new [Re: MaestroMyth]
      #4775241 - 08/29/11 08:26 AM

Quote:

Hi all,

Going to upgrade a 'free' Barlow that came with my scope.

I'm looking at the TV line and I don't understand the difference between their Barlow and Powermate. 2x, 3x, 4x, etc.

I use an 8 inch SCT for visual and astrophotography.

If not a TV offering, can anyone recommend a Barlow that would be an upgrade over my standard Parks Barlow?

Thanks in advance!




A Barlow is a 2 or 3 element "negative" lens set that diverges the light entering it. This increases the magnification that an eyepiece will deliver, but with some wider-field eyepieces, the Barlow can diverge the light enough that some of it actually misses the field lens of the eyepiece. This can produce some vignetting in the outer parts of the field. A Powermate also increases the magnification, but uses two sets of lenses to do that: a smaller two-element doublet negative lens set, and a somewhat larger two element positive doublet lens set some distance behind the negative doublet. The larger positive lens set reconverges the light from the negative lens to some degree and thus avoids the vignetting problem. It produces a light cone which more faithfully re-creates the light cone from a telescope with an intrinsically-longer focal length, rather than only approximately doing it like a Barlow does. This can be important for some solar H-alpha filters that require very long true f/ratios in excess of f/30. A Barlow will also increase the eye relief of most eyepieces, which may or may not be a beneficial thing. If it extends the eye relief too much, it can be hard to get or keep your eye in the right location to catch all the light. The Powermate on the other hand does not increase the eye relief of the eyepiece significantly. Barlows usually require some inward focus travel to work, which can be a problem with telescopes that do not have enough focus travel. The Powermate by contrast requires only a small amount of *outward* focuser travel in order to work, so with some scopes, it can achieve focus when a Barlow would not. Clear skies to you.


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Barlow vs. Powermate? new [Re: David Knisely]
      #4776786 - 08/29/11 10:09 PM

It seems like in most cases, the Powermate is the way to go????

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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Barlow vs. Powermate? new [Re: GeneT]
      #4777133 - 08/30/11 12:38 AM

Quote:

It seems like in most cases, the Powermate is the way to go????




It can be a good choice, although a good Barlow like the Tele Vue 2" 2x model can also do the job. I do like the Powemates, as with my Newtonian before I shortened the trusses, the Barlow would not come to focus due to insufficient inward focus travel. My 2.5x Powermate avoided that problem and gave me excellent performance. Now that I have shortened the trusses, I am now looking around for a 2" barrel "image amplifier" which may turn out to be a Powermate or a Tele Vue Barlow. Clear skies to you.


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David Knisely
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Loc: southeastern Nebraska
Re: Barlow vs. Powermate? new [Re: ischua]
      #4777141 - 08/30/11 12:42 AM

Quote:

A Powermate is a corrected barlow no aberrations.
You can unscrew the 2" eyepiece housing and screw on a T-ring adapter for attachment of CCD or camera




Well, there is nothing really wrong with a Barlow, so Powermate isn't really a "aberration corrected" Barlow. The only thing the Powermate corrects for is mainly that divergent light which can induce the outer field vignetting in some wider-field eyepieces. Most decent Barlows do not introduce much in the way of significant aberrations, as they tend to be well-corrected. Indeed, some Barlows can also be screwed onto eyepieces or camera adapters. Clear skies to you.


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bgavin
scholastic sledgehammer
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Reged: 01/25/11

Loc: 38°41' x 121°13'
Re: Barlow vs. Powermate? new [Re: David Knisely]
      #4926233 - 11/20/11 02:08 PM

Q: Does either Barlow or Powermate use only the very center of the scope's image circle?

My question is framed for refractors and field flatteners.
If only the center is used, this should be much more flat than the far corners.

I'm trying to determine if a field flattener is required when using a Powermate for prime focus imaging.


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Benach
Pooh-Bah


Reged: 01/24/08

Re: Barlow vs. Powermate? new [Re: ischua]
      #4926507 - 11/20/11 05:08 PM

Quote:

A Powermate is a corrected barlow no aberrations.
You can unscrew the 2" eyepiece housing and screw on a T-ring adapter for attachment of CCD or camera




Uhm, no, you're mistaken here. They're two totally different thingies. A Barlow is a negative group that puts the focus further away:
http://www.cloudynights.com/ubbthreads/attachments/1442094-Bravais%20Barlow.gif
A Powermate is a telecentric system. That means that the wavefront is enlarged.
http://t1.gstatic.com/images?q=tbn:ANd9GcTtgPux0-RLe13wKDPv3xLCeCX1lsvDHQNQ2vB7nFAEl9fgVjk4dkJOX79Q


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simpleisbetter
Carpal Tunnel
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Reged: 04/18/11

Re: Barlow vs. Powermate? new [Re: Benach]
      #4926561 - 11/20/11 05:46 PM

MaestroMyth,

Benach's actually correct in his description, they are two different things. TV's website actually does a good job describing the differences. But Ischua's observation about being able to attach a camera directly to a Powermate (using the appropriate TV Powermate adapter) is also right, and a plus when it comes to planetary imaging (and that's about the extent of my imaging knowledge...).

Since your stated goal is visual and some AP with your C8, I'd recommend the 2x Powermate.


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bgavin
scholastic sledgehammer
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Reged: 01/25/11

Loc: 38°41' x 121°13'
Re: Barlow vs. Powermate? new [Re: simpleisbetter]
      #4926731 - 11/20/11 07:17 PM

I have both 2.5x and 5.0x Powermate in 1.25".
Both have the barrels unscrewed, and the optics screwed into a Televue T2 ring (male) for Powermate.
These mate with a standard T-ring on my Nikon.


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Benach
Pooh-Bah


Reged: 01/24/08

Re: Barlow vs. Powermate? new [Re: bgavin]
      #4927158 - 11/21/11 12:49 AM

bgavin: I wonder, what is the fully illuminated FOV for a 1.25" powermate?

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michael_m
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Reged: 11/16/10

Loc: Mount Vernon, Wa
Re: Barlow vs. Powermate? new [Re: Benach]
      #4927180 - 11/21/11 01:23 AM

Mr. David Knisely,

When you say that the PowerMate only needs a small amount of outward focuser travel to work, how much are we talking about? For example, my 8mm Ethos, my farthest outward focusing lens, leaves me with approximately 1/4" of remaining outward focus. Is that enough to use it on the 8mm Ethos?


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ThreeD
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Reged: 12/23/08

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Re: Barlow vs. Powermate? new [Re: michael_m]
      #4927715 - 11/21/11 12:11 PM

It's so close that it's practically parfocal -- no where near 1/4". (At least for the 2.5x and I from what I've read I believe it is true for all of them.)

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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Barlow vs. Powermate? new [Re: michael_m]
      #4927815 - 11/21/11 01:10 PM

Quote:

Mr. David Knisely,

When you say that the PowerMate only needs a small amount of outward focuser travel to work, how much are we talking about? For example, my 8mm Ethos, my farthest outward focusing lens, leaves me with approximately 1/4" of remaining outward focus. Is that enough to use it on the 8mm Ethos?




I generally have to use around 1/4 inch outward focus for my 2.5x Powermate. However, I can slide the Powermate itself outward and lock it in place with my focuser set screw or use an extension tube if I need to. Clear skies to you.


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johnnyha
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Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Barlow vs. Powermate? new [Re: David Knisely]
      #4928054 - 11/21/11 03:15 PM

It is crazy how much outward focus is required for the 8mm Ethos, one reason I switched back to using my 7mm Pentax XW. Probably over an inch more than any of my other EPs including 13 and 10 Ethoi. It's the kind of eyepiece that can require you to add an extension tube to reach focus.

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dvb
different Syndrome.
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Reged: 06/18/05

Loc: Vancouver, Canada
Re: Barlow vs. Powermate? new [Re: johnnyha]
      #4928301 - 11/21/11 06:02 PM

Sounds like a Barlow might be good choice for eyepieces like Plossls and Orthos with shorter eye relief, to allow more comfortable eye relief when reaching into the higher powers.

Sounds like the Powermate would be a good choice at the lower focal lengths, with wider field eyepieces.


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Barlow vs. Powermate? new [Re: MaestroMyth]
      #4928758 - 11/21/11 11:09 PM

I bought a 2X Televue Powermate; it is an excellent optic.

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Danzup77
professor emeritus


Reged: 09/12/11

Re: Barlow vs. Powermate? new [Re: GeneT]
      #4929027 - 11/22/11 06:22 AM

I have a 2X and a 4X powermate and LOVE em....well I only use the 2X. I actually got the 4X as kind of an early christmas present although I have no idea how I will use it....lol. Guess I just need a 30-something mm piece now to give it some use lol.....
Honestly if it wasnt for these folks here I wouldnt know 10% of what I know now....


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michael_m
sage
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Reged: 11/16/10

Loc: Mount Vernon, Wa
Re: Barlow vs. Powermate? new [Re: Danzup77]
      #4929965 - 11/22/11 05:45 PM

Another solution that can work, depending on your circumstances, is to put a "riser" on the body of the focuser. In my case the circumstances match well.

I have the Starlite Feathertouch. My focuser protrudes into the UTA about 5/8" when fully racked inwards. So I loose that amount of focuser travel. I should have mounted the focuser board outwards more when I built the UTA. Rookie mistake. So I just bought the R20-0.65" riser and now will have all the outwards focus I could ever need while not protruding inside the UTA when racked all the way in.

It's a good solution, especially since I don't have the mirror yet and the truss pole length has not been set up to my most inwards focusing lens. I know I'll be using a PowerMate 2X when conditions allow. True, I may not have needed to add the riser, at least according to ThreeD, but now I will have the full focuser travel available and I know the 8mm Ethos, or even a 6mm future Ethos, will come to focus no matter what while using the PowerMate.


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ThreeD
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Reged: 12/23/08

Loc: Sacramento suburbs
Re: Barlow vs. Powermate? new [Re: michael_m]
      #4930564 - 11/23/11 01:12 AM

Quote:

I know I'll be using a PowerMate 2X when conditions allow. True, I may not have needed to add the riser, at least according to ThreeD, but now I will have the full focuser travel available and I know the 8mm Ethos, or even a 6mm future Ethos, will come to focus no matter what while using the PowerMate.


I can only speak to the 2.5x from personal experience but note that TV says they are essentially parfocal in point 4.

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michael_m
sage
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Reged: 11/16/10

Loc: Mount Vernon, Wa
Re: Barlow vs. Powermate? new [Re: ThreeD]
      #4931219 - 11/23/11 12:39 PM

Although I had not seen that "point 4" yet while researching, which I have now done, I did not doubt you ThreeD. The riser is more about getting the fully racked in focuser out of the inside of the UTA and also the full focuser travel for whatever I might do in the future. Thanks for your assurance from experience and your input.

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Startraffic
professor emeritus
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Reged: 02/12/06

Loc: Lat. 39.143345, Long. -77.1748...
Re: Barlow vs. Powermate? new [Re: ThreeD]
      #5518260 - 11/13/12 04:39 PM

MaestroMyth,
I have 2 Powermates, both 2" a 2x & 4x. I don't care for the views through a Barlow. They are however, pretty cheap ones. Something that no-one has mentioned, Powermates are significantly heavier, You'll need a solid focuser to carry one. I replaced a GSO I had on my SNT with a Moonlite, much better.

Clear Dark Skies
Startraffic
39.138274 -77.168898
Alt 518ft ASL


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Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Barlow vs. Powermate? new [Re: Startraffic]
      #5670222 - 02/09/13 07:23 AM

Thank you for a very interesting discussion. Since some time has elapsed since the last post, I hope folks don't mind if I resurrect it and ask some related questions.

I recently bought a smaller refractor, and, unsurprisingly, I find that the eyepieces I had for my 8 inch SCT do not give high enough magnification for planets.

I have been thinking of upgrading my Celestron Barlow that came bundled with my SCT. Would a TeleVue 2x Barlow or PowerMate (or other product) give noticeably improved performance?

This is for a 90mm F7 Refractor. The highest magnification ocular that I have is 8.8ES82. (I also have 11mm and 14mm that could be barlowed.)

But I am not committed to the Barlow route. I guess mine is actually more of a general question regarding eyepiece strategy for this unfamiliar focal length.

Also I'm curious as to the purpose of the 2 inch Barlow or PowerMate discussed above. Intuitively, it seems like this type of amplifier would be used more for achieving high magnifications. But I'm sure I'm missing something. Any remediation of my benightedness would be greatly appreciated. Maybe people use them for the 9mm Ethos?

Cheers,
David


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Barlow vs. Powermate? new [Re: Widespread]
      #5670814 - 02/09/13 01:54 PM

Quote:

Thank you for a very interesting discussion. Since some time has elapsed since the last post, I hope folks don't mind if I resurrect it and ask some related questions.

I recently bought a smaller refractor, and, unsurprisingly, I find that the eyepieces I had for my 8 inch SCT do not give high enough magnification for planets.

I have been thinking of upgrading my Celestron Barlow that came bundled with my SCT. Would a TeleVue 2x Barlow or PowerMate (or other product) give noticeably improved performance?

This is for a 90mm F7 Refractor. The highest magnification ocular that I have is 8.8ES82. (I also have 11mm and 14mm that could be barlowed.)

But I am not committed to the Barlow route. I guess mine is actually more of a general question regarding eyepiece strategy for this unfamiliar focal length.

Also I'm curious as to the purpose of the 2 inch Barlow or PowerMate discussed above. Intuitively, it seems like this type of amplifier would be used more for achieving high magnifications. But I'm sure I'm missing something. Any remediation of my benightedness would be greatly appreciated. Maybe people use them for the 9mm Ethos?

Cheers,
David




The Barlow or Powermate would give you very good performance as good as or perhaps slightly better than the Celestron Barlow. With a Barlow, the eye relief of an eyepiece can be maintained or increased slightly which can help with some eyepieces that don't have a lot to begin with and hurt with others if the Barlow puts in too much eye relief. Powermates also maintain eye relief, but they don't increase it. As for why 2" Barlows or Powermates are used, that is for use with longer focal length 2" barrel eyepieces. The use of these is especially prevalent in the larger Dobsonians, where longer focal length wider-field eyepieces are often used and higher powers are desired. Clear skies to you.


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Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Barlow vs. Powermate? new [Re: David Knisely]
      #5670933 - 02/09/13 03:46 PM

Thank you, David. As good or slightly better... It sounds like any improvement would be minor.

I think I understand what you are saying about 2" barlows: 2" finder EPs to locate a target, then Barlow for a better look, e.g.

Cheers,
David


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Barlow vs. Powermate? new [Re: Widespread]
      #5671877 - 02/10/13 06:44 AM

Quote:

Thank you, David. As good or slightly better... It sounds like any improvement would be minor.

I think I understand what you are saying about 2" barlows: 2" finder EPs to locate a target, then Barlow for a better look, e.g.

Cheers,
David




David:

I have two older Celestron Shorty Barlows, I use them with some pretty good eyepieces and telescopes, I have other Barlows but the Celestron Shorty's are my favorites. I only use them for high magnification, when 3.5 mm Nagler or 4mm TMB Planetary is not enough, I think your current Barlow will do a good job.

Jon


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Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Barlow vs. Powermate? new [Re: Jon Isaacs]
      #5672044 - 02/10/13 09:48 AM

Hi Jon,

It's good to hear that I don't need to spend more for an expensive diagonal.

Funny you should mention the TMB 4mm. In fact, I was trying to decide whether to get one of those; or a better Barlow; or just stick with my current Barlow.

I'm now leaning against an expensive Barlow, and figured that my 8.8mm, when Barlowed, would be about as high mag as 90mm could handle.

Those TMBs look nice, though. How much improvement could one expect from the 4mm and 5mm planetaries, compared with Barlowing my 8.8 and 11mm ES82s?

Best,
David


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johnnyha
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Loc: Sherman Oaks, CA
Re: Barlow vs. Powermate? new [Re: Widespread]
      #5672852 - 02/10/13 06:46 PM

I'm pretty sure your ES 82s when barlowed will be of somewhat higher quality than the TMBs. I think you're good actually. The TMBs are nice for the price but they are not premium optics like the ES 82s. Your ES82s will barlow well at 2X giving you a *perfect* progression from 14, 11, 8.8mm to 7, 5.5, and 4.4mm.

If you have any doubts about the Celestron barlow then you can grab a nice used 1.25" 2X TV barlow for around $70.


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Motokid600
super member


Reged: 06/27/10

Loc: Berlin, New Jersey
Re: Barlow vs. Powermate? new [Re: michael_m]
      #5674069 - 02/11/13 01:28 PM

Imaging the planets is something I've been wanting to get into. I've got a 1000d in prime focus behind a CPC11 and I find the magnification is not significant enough for when it comes to planets. Im not to savy with magnigication details so ill say this. At my current focal length I can just barely fit the whole moon into my camera's FoV. Not enough.. so with backyard EoS I can record via the live view. The power mate seems to be the way to go. But which one? 2x or 4x. My goal one day is to be able to achieve detail on the Jovian moons. So would a 2x do the job? I realize a 4x would be at the mercy of the atmosphere, but surprisingly this small, light polluted town of mine seems to be blessed with some stable air above it.

Edited by Motokid600 (02/11/13 01:34 PM)


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Jim Romanski
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Re: Barlow vs. Powermate? new [Re: Motokid600]
      #5674768 - 02/11/13 08:38 PM

I've read that planetary imagers will stack Powermates to get higher maginfications. So I guess you could get a 2X and see if it's enough. If not you could get another or a 4X then you'd have 2X, 4X and 6X (or maybe it would be 8X?).

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Jim Romanski
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Loc: Guilford, Connecticut
Re: Barlow vs. Powermate? new [Re: MaestroMyth]
      #5674776 - 02/11/13 08:45 PM

I have both 2" Powermates the 2X and 4X. I bought them after buying a short focal length refractor. They give me all kinds of magnifications and with any of my eyepieces. I thought I might get into planetary imaging with them as well though I haven't yet.

I also bought the older Televue 1.8X 1.25" barlow. I found that I wanted a smaller magnifier to use with smaller scopes and eyepieces. Also, I wanted the 1.8X in order to get a differnt variety of magnifications.

They all work very well.


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Jon Isaacs
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Re: Barlow vs. Powermate? new [Re: Motokid600]
      #5675302 - 02/12/13 06:22 AM

Quote:

Imaging the planets is something I've been wanting to get into. I've got a 1000d in prime focus behind a CPC11 and I find the magnification is not significant enough for when it comes to planets. Im not to savy with magnigication details so ill say this. At my current focal length I can just barely fit the whole moon into my camera's FoV. Not enough.. so with backyard EoS I can record via the live view. The power mate seems to be the way to go. But which one? 2x or 4x. My goal one day is to be able to achieve detail on the Jovian moons. So would a 2x do the job? I realize a 4x would be at the mercy of the atmosphere, but surprisingly this small, light polluted town of mine seems to be blessed with some stable air above it.




From what I see, planetary imagers are using modified webcam technology and image processing techniques like stacking to produce the fantastic photos of Jupiter and Saturn. One does not need a large frame size because one is limited by the resolution of the scope, only so many pixels are needed. Jupiter is only about 40 arc-seconds in diameter if you are oversampling and using 0.25 arc-seconds/pixel, this is only 160 pixels x 160x pixels. They key is transferring at 30 or 60 frames per second uncompressed video, getting a lot of data and then processing it to increase the signal to noise ratio.

Jon


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simon j poole
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Reged: 02/11/13

Loc: UK
Re: Barlow vs. Powermate? new [Re: Jon Isaacs]
      #5677929 - 02/13/13 04:07 PM

I have 2x & 3x tv barlows, 2.5x powermate! There all very good performers but the tv 3x barlow which is a two element design produces a slightly more detailed image imho when im planetary imaging. Regards Simon.

Edited by simon j poole (02/13/13 04:13 PM)


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Jack Morris
member


Reged: 11/23/12

Loc: Louisiana
Re: Barlow vs. Powermate? new [Re: simon j poole]
      #5678850 - 02/14/13 06:48 AM

I have learned a lot from this discussion, thanks everyone. Does anyone care to comment on how the Explore Scientific "Focal Extenders" fit in here?

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MikeBOKC
Post Laureate
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Reged: 05/10/10

Loc: Oklahoma City, OK
Re: Barlow vs. Powermate? new [Re: Jack Morris]
      #5678957 - 02/14/13 08:37 AM

I have the 2 inch ES barlow/FE and it seems to work very well. Don't use a barlow that often, but images are very comparable to that I get in the 2.5 1.25 Powermate.

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Jim Romanski
Carpal Tunnel
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Re: Barlow vs. Powermate? new [Re: Jon Isaacs]
      #5681806 - 02/15/13 03:39 PM

Quote:

From what I see, planetary imagers are using modified webcam technology and image processing techniques like stacking to produce the fantastic photos of Jupiter and Saturn. One does not need a large frame size because one is limited by the resolution of the scope, only so many pixels are needed. Jupiter is only about 40 arc-seconds in diameter if you are oversampling and using 0.25 arc-seconds/pixel, this is only 160 pixels x 160x pixels. They key is transferring at 30 or 60 frames per second uncompressed video, getting a lot of data and then processing it to increase the signal to noise ratio.

Jon



I've dabbled with this kind of webcam planetary imaging a little bit (see my avatar). But I know some of the guys who do outstanding work use other gear and have great results. Check out Paul Hyndman's site and you'll see he mentions using Powermates for a lot of his high power imaging.
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