The Zoom Caveat - An exception perhaps?

[Flying Eye]

Hi all,

I've been trying to come up with shortlists for various forms of optics as I learn a little more (endless hobby in itself).

I accept the advice that the zoom feature is to be avoided in binoculars. As far as I can tell this is down to the two eyepieces not moving in complete unison, but there may be another reason I'm not yet aware of.

I'm thinking that this is probably not applicable to spotting scopes. So, would I be right in that thought?

The majority of spotting scopes I have so far seen come with a zoom eyepiece these days, and fixed eyepieces are an optional extra available in some cases. I've not seen a vast amount of complaint about having zoom by default from users of them, but I may not have been looking in the right places for it.

I could use some clarification on this if anyone knows for sure?

[kniclander]

I would guess that for birding etc the convenience of zoom outwieghs any optical issues. For astro, when things don't get up and fly away:) i would think the reverse might be true?

[BinocularSky]

I accept the advice that the zoom feature is to be avoided in binoculars. As far as I can tell this is down to the two eyepieces not moving in complete unison, but there may be another reason I'm not yet aware of.

That is correct on both counts ; there needs to be no more than about 1% difference in zoom -- very difficult and very expensive to attain. The other reason is due to the magnification that zooms aspire to. At, say, x30, collimation needs to be within 1 arcmin; at x60 it must be within 30 arcsec. These are difficult enough to attain and maintain with good-quality kit; it's unreasonable to expect it in what is essentially low-budget gimmick kit.

I'm thinking that this is probably not applicable to spotting scopes. So, would I be right in that thought?

Right again. Zoom eyepieces can be very convenient. All but the very best tend to ghost a bit on bright objects, have tiny fields at the low-mag end, and need refocussing slightly as you zoom but, that said, a mid-range zoom (e.g. the Vixen LV 8-24mm) is a heck of a lot better than some fixed eyepieces I've encountered.

[Flying Eye]

I would guess that for birding etc the convenience of zoom outwieghs any optical issues. For astro, when things don't get up and fly away:) i would think the reverse might be true?

Yes, that was sort of my take on it.

I'm a birder first and astro is starting to nibble if not actually bite yet.

[Flying Eye]

Thanks very much indeed Steve. See, I am paying attention, and slowly some of it is sinking in!

[cantab]

Yes, the exception to the advice against zoom binoculars is when you're buying something with zoom that's not a binocular:p

[Flying Eye]

Yes, the exception to the advice against zoom binoculars is when you're buying something with zoom that's not a binocular:p

DOH! Wish I was that bright!