should focus change when zooming?

carteriii · Guest

I'm a total newbie with a new PF65-ED II and the Vixen 8-24mm zoom eyepiece which I recently purchased from you.

Should the focus change when I change the zoom on the eyepiece? I ask because I do have to change the focus whenever I zoom more than ~10-20% of the range, but I didn't expect to have to do so. I've never used a spotting scope before, so my only real experience is with binoculars in which I'd focus while zoom'ed in, and then always maintain that focused image after zooming back out. With this scope and eyepiece, I find that to be impossible. The focus at 8mm is simply different than it is at 24mm or anywhere in between.

If that's just the way it is, so be it. But if I have a bad eyepiece or mounted it wrong, I'd like to know. Thanks in advance.

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5173

Hi

Yes, some focusing is always required as you zoom up in magnification. There are some zooms that are parfocal as you back down in magnification, but not all zooms offer this feature. It is typically found only on premium spotting scope eyepieces. Even then, as features go, it is not especially useful, since you are almost always working your way up in magnification when using a spotting scope, not down. Nothing wrong with your eyepiece as long as it is focusing.
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Guest · Posted: Thu Apr 24, 2008 8:07 am Post subject:

That's exactly what I needed to know. Sounds like everything is as it should be. Thank you so much.

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5173

You are very welcome.
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