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field on TV76

Started by RobertHowe, 12/09/2008 09:32AM
Posted 12/09/2008 09:32AM | Edited 12/09/2008 09:36AM Opening Post
Hi all

I am trying out a used TV 76. My TV 85 and 102 and Genesis all had perfect point stars across the entire field, so this is the performance that I expect of the 76.

Last night, the 76 showed comets everywhere peripherally, which came to focus--but then the center was out of focus. There was an area (lower left as one sights through the scope) in which no star would focus, they were either wide or double as I focussed in and out.

I used AP and Televue diagonals; EPs included TV 35, 24 and 19 Panoptics; 22, 13 and 9 Naglers; 13 and 8 Ethos. Only the 9 mm Nagler, with the smallest FOV, showed no aberrations; the 8 mm Ethos showed less than any of the others. But the entire FOV of the 9 Nagler would be the central image of the 22 Nagler.

Looking at the moon with a 19 Panoptic, one limb would be clear and the opposite, out of focus.

A star test showed the enlarged image to be considerably out of round. The telescope was well equilibrated when I observed and my TV85 worked perfectly as did a Tak 60.

Any thoughts?

Robert Howe

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RobertHowe's attachment for post 44865

Robert Howe
Wilbraham MA

TeleVue 85 f/7 // Astro-Physics Traveler 105 f/6 // Astro-Physics 130 f/8.35 // TEC 180 f/7
Coronado 60 DS
"Scopes, Brains and Wisdom--but no Beauty"
Posted 12/10/2008 06:50AM #1
Hi there. Seems like you might have a collimation problem. My TV-76 had amazing pin point performance with any eyepiece. I actually preferred it to my TV-85.