TV Powermate field stops vs barrel size makes no sense.
Hey all,
I'm trying to understand why the TV 4x powermate is a 2" barrel, when the field stop is around 18mm? Surely that would fit in a 1.25" package given the size of the field stop?
It also seems a little weird that the 2 and the 4x are 2", but the 2.5 and the 5x are 1.25".
Is there any rhyme or reason to this? It makes no sense!
I have the full compliment of Powermates used for both observing and planetary imaging.
Totally agree it seems strange
The only reason I can think of why the 4x was designed with a 2” barrel as historically the 2x and 4x are probably the most commonly used Powermates for imaging out of the whole set.
I have the full compliment of Powermates used for both observing and planetary imaging.
Totally agree it seems strange
The only reason I can think of why the 4x was designed with a 2” barrel as historically the 2x and 4x are probably the most commonly used Powermates for imaging out of the whole set.
So perhaps something to do with a 2" design being less prone to sagging in the imaging train?
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).
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).
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.
