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Powermate vs Eyepiece Projection

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#1 Andrewf

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Posted 30 November 2012 - 08:05 AM

I haven't posted in years but I finally have a question for this forum. I want to get back into lunar and planetary imaging with a webcam. I have done a lot with a C8/2x Barlow/NexImage. Now I'm interested in eyepiece projection using the C8 and my NexImage. I'm also interested in whether a Powermate would be a better choice that eyepiece projection. Has anyone gone down this path? Does anyone use eyepiece projection? I know Powermates are popular. Any advice would be appreciated.

Thanks!

Andy

#2 jgraham

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Posted 30 November 2012 - 09:20 AM

I've used eyepiece projection, Barlows, and Powermates. PowerMates work very well if the amplification matches what you need. I liked the fact that you could vary the amplification of eyepiece projection with extension tubes, but you need a high quality eyepiece and this tends to put a lot of lenses in the light path. The method I use most often is a Barlow with a small extension tube to get me to f/30. This has proven effective and places only a small number of lenses in the light path (I believe that mine's a doublet). I like my Powermates, but I had to choose between f/25, which was a tad short, and f/50, which was too long. Sooooo, for me it's Barlows for imaging, Powermates for visual, and eyepiece projection for historical value. :)

#3 drksky

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Posted 30 November 2012 - 11:26 AM

Call me confused, but what's the difference between a Powermate and a barlow? I thought Powermate was just Televue's line of barlow lenses.

#4 Larry F

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Posted 30 November 2012 - 02:41 PM

No, Powermates have a different lens design than a Barlow. See David Knisely's CN review.

#5 DesertRat

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Posted 30 November 2012 - 04:21 PM

With a C8 I would stick to the use of a barlow or powermate. Eyepieces are sometimes used to get the higher efl's on shorter focus newtonians. Many newt owners are now using extended 3X barlows or the 5X powermate.

Eyepieces are not really designed for projection with the exception of some special types from Takahashi and Pentax, which are getting hard to come by now.

Glenn

#6 azure1961p

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Posted 30 November 2012 - 07:35 PM

Correct me if I'm wrong but eyepiece projection would yield a larger planetary image than could fit in the frame. At the very least I think it'd be to large and comparitively dim. What ever gets you approximately f/25 is in the ballpark. The relatively emmense projection images aren't needed with today's came as they are extremely efficient and small unlike the old negative film size of an old already.

Good luck.

Pete

#7 DesertRat

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Posted 30 November 2012 - 08:09 PM

If you start at f/5 or so a carefully selected eyepiece can get you to f/25 to 30. Zac Pujic used a 9mm Nagler with the barlow part removed to image Mercury with his 12" newtonian. You can see an example here.

For reasonable f ratios in the ccd era you would have to use fairly long focal lengths around 25mm or so, and many of those will not fit in todays projectors. I don't recommend it, as said earlier they really are not designed for projection and will add a fair amount of undercorrection. If you start overcorrected the result could be useful I suppose.

Microscope objectives are designed for projection, but thats another story, and quite expensive if done properly.

Glenn

#8 skywatch

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Posted 30 November 2012 - 08:54 PM

I've used eyepiece projection. Barlows are better because you'll get a flat field. Also with a barlow you can more easily enclose the entire light path using standard adapters, keeping out dust and stray light.

-Rolf

#9 skywatch

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Posted 30 November 2012 - 08:58 PM

No, Powermates have a different lens design than a Barlow. See David Knisely's CN review.


But that compares a Meade barlow to a powermate. I think comparing to a powermate to a Televue barlow would be fairer.

-Rolf

#10 jgraham

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Posted 30 November 2012 - 09:32 PM

I think that there is a good discussion of Powermates versus Barlows on Televue's web site.

#11 Andrewf

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Posted 01 December 2012 - 08:30 AM

Thanks everyone! I think I will look into the Powermate. I've read and heard also that it can be difficult to focus using the eyepiece projection. It doesn't hurt that the Powermates are on sale :)

Andy

#12 tjensen

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Posted 01 December 2012 - 08:49 AM

I have an Orion Shorty 2x and tried a Televue 2.5 powermate. The Powermate didn't fit snugly into my filter wheel and I had some flex issues. The modern barlows are pretty high quality and I think you would be hard pressed to go wrong with one. The Televue Powermates have a great rep (I have one of their 3x barlows but don't use it much anymore)and are parafocal with their eyepieces which can be handy.

#13 Maau the Lynx

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Posted 09 December 2012 - 12:32 AM

I also have similar query regarding high quality amplifier for planets. Essentially it looks like i've maxed out with what i can do with current equipment. Here is recently taken Jupiter with skywatcher 6" f/5 Newt, Meade 25mm plossl-Meade Eyepiece projection kit & Canon 600D. Crop zoom factor pushed to 10x & variable length pushed to max. Jupiter fills sizable frame. Thus now thinking about 5x powermate to do the same with less weight & may be better images owing to top notch optics.

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