Powermates v. Barlows

[robin]

Hi all, can any one give me the good oil on whether or not the Televue powermates leave 'ordinary' barlows such as Meades, Orions or Celestrons in their wake.Are they much better, a lot better, a bit better???
Any comments?
Im thinking about the TV 2.5X powermate for the LX200.
Thanks.

[Jonathan]

The Powermate is better! I've got a 2.5x Powermate in 1.25" and a cheap Meade 2x barlow. To my inexperienced eyes the Powermate is a bit sharper even with the extra magnification, and so it should be at nearly 5 times the price.

[asimov]

What I would like to know is WHY their better..Are they not just a barlow that gives more magnification than a standard 2X one?

[Jonathan]

Different optical design to a Barlow, but I'm no expert. This explains it in detail - http://www.televue.com/engine/page.asp?ID=42

[asimov]

Ah Yes! Thanks Jonathan. That certainly explains it fully to me. Cheers!

A power-mate is now on the list of 'getting one...one of these days!'

[janoskiss]

So a powermate is "a bit sharper" than a cheap Meade Barlow. That does not really justify the huge price diff. What about a good apo Barlow, like the Shorty Plus, which is still less than half the cost of the Powermate? Or the 2" UO barlow, that comes so highly recommended by Dave (see reviews), at around half the cost of a 1.25" P-mate?

[mickoking]

As an owner of a couple of Televue eyepieces (13mm Nagler, 27mm Panoptic) I can proclaim they are great eyepieces, and I am sure their other products are of the same high quality.

BUT

I dont believe the expense is justified. An andrews sv 20mm e/p cost about $70- and from what I remember the two televiews cost around $700-. That is a 10 times difference in price. The difference in quality between the Andrews and Televue eyepieces is not 10 times, expecially considering the sv has (slightly) better light transmission.

I guess Televue will continue to charge outrageous prices while people are prepared to pay those prices. But with Chinese and Taiwanese manufactures rapidly improving their products Televue may have some stiff competition in the future but then again there will always be a market for overpriced premium products, just look at Questar.:D

[gbeal]

I have a foot in both camps, being miserable as, but owning good gear. I used all manner of Barlows, and now use a 5x and a 2.5x Powermate, nothing else (well apart from a 2x Zeiss Barlow but thats another story).
I have tried all manner of eyepieces as well, but now have a couple of Naglers (22mm & 12mm) and a set of Zeiss orthos (4mm - 25mm).
Better than the cheap ones I tried/owned/sold???????? Who knows, but part of the warm and fuzzy feeling that I demand when I observe is actually getting that warm and fuzzy feeling. I know that if a planetary view isn't sharp with my scope and Zeiss ortho, then I must have sore eyes, or the seeing is not up to it.
In answer to the original question though. Best bet is sidle up to someone who is imaging and get them to do a subjective on the spot series of avi's with a Powermate and an elcheapo, best way to answer it.

[asimov]

Hmm. I have a 2X APO series 4000 meade & I quite like it, but then...I have nothing else to compare it to. If there's something out there that gives better images, I'd be interested in knowing about it..

[janoskiss]

Maybe someone will bring a Powermate along to Star Camp, and we might do side by side comparisons.

[ausastronomer]

I am a purely visual observer and currently own a 2.5X TV powermate, a 2X Orion Shorty Plus and a 2" 1.6X Antares APO barlow. I previously owned a 1.25" 1.8X Televue barlow and I have also used numerous other barlows going back over a lot of years. The 2.5X TV powermate is the best barlow I have ever used. Its not an enormous deal better than the TV 1.8X and the 2X Orion Shorty Plus but its better, possibly by 5% to 15% or so depending on your eyepieces and telescopes. With "ALL" other barlows you have the feeling that something else is in the optical path, even though image quality is superb, with the powermate you don't even know its there and you think you are just using a native eyepiece. Since I have owned the powermate I haven't used the Orion Shorty Plus and its a very good barlow in its own right.

Considering that all your eyepieces are top quality as are your scopes, I think its worth spending the extra on the powermate.

CS-John B

[Miaplacidus]

What about these new Meade TeleXtenders (an Bintel's website)? Are they Powermate clones (at about 2/3 the price)? Wonder how they compare. Anyone tried them or read any reviews?

Cheers,

Brian.

[janoskiss]

I asked about Meade TeleXtenders at Astro Optical's Melbourne shop, and I asked precisely what you're asking, Brian: "Are they Powermate clones?" I was told that they are only for photography, because they produce a flat field, and that I would be wasting my money buying them for visual astronomy.

But the guy I spoke with (looks like he's the owner) did not seem to know much about Televue products. Had no idea about Naglers... :shrug: Still, he seems to be a keen amateur astronomer with above average experience. (Last year he helped collimate my crappy 114mm DSE Newtonian and talked me out of buying anything from the shop until I took my time with the basics. :thumbsup: to him for that.)

[davidpretorius]

http://www.televue.com/images/eyepieces/PowermatePowerIncrease.gifOk, I want to image the planets with my toucam in as high a magnificatio that i can.

I notice from this chart, the 5x can get as high as 7.5x by varying the position.

I would be using the toucam in prime focus i would assume, ie a fl of roughly say 5mm ie 1250/5 = 250x x 5 for televue = 1250 x minimum!

For guys with the televue 5x, can you easily vary the position from the top surface with a toucam in prime focus mode ie the lens from the toucam removed!

Ice is this the unit you are looking at?

[gbeal]

Now you can see why I use the 5x!!

[davidpretorius]

they talk a lot in reviews of the 7.7, can you really get that! and is it via eyepiece projection, prime focus???

[anthony2302749]

Hi David

I have used a 2.8x Klee Barlow Lens and am now using a 5x Powermate for planetary imaging. Both of these Barlow’s are used widely by Planetary Astrophotographer’s.

The main reason I use these Barlow’s is that they are well corrected for aberration. The Klee for example, is a 3 element Apochromatic Barlow which is well corrected for spherical aberration and longitudinal and lateral colour. I have used a standard 2x Achromatic Barlow while imaging Mars, with most images ending up with a slight blue fringe. The Klee solved this problem as well as increasing the f/ratio of my scope to 28.

If your plans are to seriously get into planetary imaging I would suggest a good Apochromat Barlow Lens.

Now, how much magnification should be used when imaging the planets? Ideally, an image scale of about 0.25 arcseconds/pixel is recommended. This should reveal the most detail possible under good seeing conditions without too much magnification. The required focal length depends on the size of the pixels in CCD camera. For a typical webcam of 5.6 micron, the required focal length would be 4600mm.

But in the real world we are talking about focal ratios as high as f/60. With my setup, I end up with a focal ratio of 50 (Meade 10” f10 plus 5x Powermate) which gives an image scale of 0.12 arcseconds/pixel exceeding the 0.25 arcseconds/pixel recommended.

Other things to consider is resolution and contrast which is best explain by Damian Peach http://www.damianpeach.com/simulation.htm (http://www.damianpeach.com/simulation.htm)

Understanding Resolution and Contrast
Two points it is important to understand is the resolution a telescope can provide, and how the contrast of the objects we are imaging affects is related to what can be recorded. Its often seen quoted in the Dawes or Rayleigh criterion for a given aperture. Dawes criterion refers to the separation of double stars of equal brightness in unobstructed apertures. The value can given given by the following simple formula:

115/Aperture (mm.) For example, a 254mm aperture telescope has a dawes limit of 0.45" arc seconds. The dawes limit is really of little use the Planetary observer, as it applies to stellar images. Planetary detail behaves quite differently, and the resolution that can be achieved is directly related to the contrast of the objects we are looking at. A great example that can be used from modern images is Saturn's very fine Encke division in ring A. The narrow gap has an actual width of just 325km - which converts to an apparent angular width at the ring ansae of just 0.05" arc seconds - well below the Dawes criterion of even at 50cm telescope. In `fact, the division can be recorded in a 20cm telescope under excellent seeing, exceeding the Dawes limit by a factor of 11 times!. How is this possible?.

As mentioned above, contrast of the features we are looking at is critical to how fine the detail is that we can record. The Planets are extended objects, and the Dawes or Rayleigh criterion does not apply here as these limits refers to point sources of equal brightness on a black background. In fact it is possible for the limit to be exceeded anywhere up to around ten times on the Moon and Planets depending on the contrast of the detail being observed/imaged.

[iceman]

yep, it's AU$310 from Bintel.