A question for fellow splitters. Are there any advantages (less light scatter, better contrast, less aberrations) for use of Powermates over TV barlows for high power visual observing (double splitting and planetary)?
Barlow vs Powermate for tight splits
Posted 19 February 2020 - 03:06 PM
I'm not a "splitter", but I'd think the barlow would provide less scatter and better contrast. Certainly center of field.
A TV Barlow is two elements in one group, so just two air to glass surfaces. A Powermate doubles that (if I remember correctly a powermate is 4 elements in two groups).
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Posted 19 February 2020 - 04:43 PM
I think it's so close, as to be impossible to tell. Everyone, more or less, says both the TV barlows and the Powermates are invisible in the final image. Several I've heard call the Powermates the sharpest "barlows" they've seen.
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Posted 20 February 2020 - 08:42 AM
I'm in agreement with Thomas. I have a TV barlow (2x) and a Powermate 2.5x. Obviously not direcrly comparable with the same eyepiece, but with each of them it's as if they're not there in terms of light scatter or sharpness. They get out of the way. Indeed, with my short f-ratio refractor at f/5.7 (petzval arrangement) I find the Powermate view is better than similar magnification with an eyepiece alone. That's with TV and Pentax eyepieces. The 2x barlow isn't quite as good as the Powermate, but still gives a little improvement compared to a straight eyepiece only.
I get similar results with my Mewlon 210 - not the same degree of improvement (f/11.5 vs f/5.7) with the Powermate, only slightly better; with the barlow as good as an eyepiece, perhaps not better. That applies to light scatter as well.
I've used various barlows over the years, though I've not tried all of them. I've yet to see a better barlow than the TV versions, though I've seen one or two that were similar. I've seen quite a few inferior, sometimes considerably inferior. I can see why barlows would get a bad rap after some of the lesser ones.
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