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Using a 1.25" Barlow on a 2"/1.25" ep

Started by astroboy314, 12/20/2002 01:46PM
Posted 12/20/2002 01:46PM Opening Post
Hello, can you use a 1.25" Barlow on a 2"/1.25" ep in a 2" diagonal? I have the Celestron 2x Ultima Barlow and am curious if I could use it on the Panoptic 22mm? I have a 2" diagonal that will accept either 2" or 1.25" eps.

Thanks!

Dave
Posted 12/20/2002 02:08PM #1
Even if you can get the the 1.25" barlow into the 2" diagonal, you won't be able to get the 2" eyepiece inside the 1.25" barlow, no matter how hard you push
Posted 12/20/2002 05:54PM #2
The big question is whether you will get vignetting of the image or not. I have an Orion Shorty Plus 3 element barlow (which, as far as I know is basically the same as the Ultima model) that vignettes the image of some 1.25" eyepieces. The interesting part is that the effect has a lot to do with the position of the eyepiece's field stop in comparison to its barrel, as well as the eyepiece focal length (longer focal lengths are more likely to vignette). Eyepieces with field stops inside the element groups will also have varying degrees of vignetting depending on the design. Really, the only way to know for sure is to try the combination to see what happens. Televue's powermate devices elliminate this problem but are expensive. If no one else has replied regarding this particular combination, I will try the combination the next time I observe with my fellow club member that has a 22 panoptic. My guess though would be that the image will be vignetted to some degree.
Posted 12/20/2002 06:07PM #3
David,

I use a 22 Pan with a shorty Barlow and a Powermate, both 1.25. You gotta remember that the 22Pan and similarly mounted Televue eyepieces are really 1.25 eyepieces. THe 2 inch part of the 1.25/2 barrel is for convenience and has no real optical effect (except shifting where the eyepiece focuses, depending on focuser).

Alex