[ausastronomer (John Bambury)]

Originally Posted by astro744

They’re not just for imaging. The 1.25” version can be used on 1.25” only system such as TV-60. I am yet to see a difference between a Tele Vue 8mm Plossl with 5x Powermate and Vixen HR 1.6mm using a TV-60 when viewing Venus. (Further tests yet to be done).

See https://www.televue.com/engine/TV3b_...d=53&Tab=_back

and https://www.televue.com/engine/TV3b_...id=53&Tab=_app

Visually they are superior to Barlow’s in they do not alter the exit pupil and the way the eyepiece sees the incoming rays.

That's all 100% spot on.

The 2" 4x Powermate came out in about 1998 or 1999; and the 2" 2x Powermate came out in about 2002. In those days digital imaging was only a Johnny came lately. At the time they were released it would have been as much for visual use as it was for imaging, if not more so. The fact they work really well for imaging is an added bonus. In a 2" Powermate you can use both 2" and 1.25" eyepieces. The same does not apply to 1.25" powermates, so the 2" powermates are more versatile. As Astro pointed out there are some scopes that can only accommodate 1.25" accessories hence the need for 1.25" barlows and powermates. Further they are a lot cheaper than 2" powermates and for those only using 1.25" eyepieces in them that's all they need.

Cheers
John B