Zoom vs. Focus

M40_A1

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Minuteman
Feb 11, 2010
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Is a quality variable power spotting scope expected to maintain a certain focus throughout the zoom range, or is there usually some refocus necessary when changing to a different power?
 
What diver said...

You can focus better at higher power than you can lower power so sometimes it’s just that.


That said if the spotter has a first focal reticle that can complicate things in the mechanicals a lot and result in wandering focus on zoom. I have seen very good spotters have this issue including the cheap ones.

You have to prioritize having the reticle and ocular image planes maintain exact focus, and that is easier in a straight optic like a riflescope than it is a folded image optic like a spotter or binocular.
 
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Thank you for the replies.

What's happening with mine is that if I focus at high power (40X), the image and crosshair (yes, a folded light path spotting scope) are both focused with no parallax. Say a target mils to 5 mils.

I leave the focus set and zoom out to lowest power (12X). The image still mils to 5 mils with no parallax, but both the image and crosshair are not in perfect focus any more. If I focus the image, parallax is present between the image and crosshair. In fact, I experimented and found that if I focused on an object 550 yards distant at 40X, then zoomed out to 12X, objects about 110 yard distant were in perfect focus (having not changed the focus at all).

Also, at lower powers it is like looking through a fish bowl. The image begins to noticeably distort from about 1/4 the distance from the center out to the edges, and is especially noticeable when panning. It gives me headaches after using it a short while. A manufacturer's rep swears it is within spec, but that doesn't sound right to me. It's driving me nuts!
 
Yeah, except this seems like more than a fine tune. That, plus the distortion and crosshair out of focus at lower powers make me think this isn't the way it is supposed to be, i.e. "spec".

In fact, what's really upsetting is that there were no such discrepancies when I first got it. The focus was a little stiff so I sent it in for lubrication. The only problem was the focus, but they went through it and serviced it as a courtesy, I suppose. I wish they hadn't. Heck, I wish I had just lived with a stiff focus!

Just wondering if anyone else was having the same symptoms with theirs or not.
 
The King, another question, since you have this same model, at what power do you begin to see image bending when dialing down from max power (if any at all)? Or, does the image remain steady all the way out to the edges when moving your eye around (or, conversely, when panning the scope), all the way down to 12X?.
 
A while back there was a thread here where someone said that you could not focus the Ret in the Mark 4 spotter like you can in a rifle scope of Binos etc is that true, because I have the original Bushnell version of the Mk 4 and you can focus the Retical on it's own and then adjust the focal point as well, My Leupold GR/HD does not have a Ret so it has no need for the Ret focus although it is the same scope as a Mk 4, just wondering if the Mk 4 has one or not, ?

John.
 
The Mk4 does not have a reticle focus. I used to have a Bushnell Excursion you're talking about, but sold it. I did like that the crosshair could be focused, but didn't like the peripheral distortion or that I'd have to refocus the crosshair when changing power. That's why I absolutely loved my Mk4 when I first got it. The crosshair was always in focus, and viewing through it was like looking through a window with no distortion edge to edge. But, since Leupold serviced it, it is now just like my Bushnell was, except I can't focus the reticle now that I need to. LOL!

Plus, the Excursion was quite a bit heavier, and extremely FRONT heavy, at that. It was annoying how it always wanted to drop forward. The Mk4 is light weight magnesium, and well balanced.
 
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The Mk4 does not have a reticle focus. I used to have a Bushnell Excursion you're talking about, but sold it. I did like that the crosshair could be focused, but didn't like the peripheral distortion or that I'd have to refocus the crosshair when changing power. That's why I absolutely loved my Mk4 when I first got it. The crosshair was always in focus, and viewing through it was like looking through a window with no distortion edge to edge. But, since Leupold serviced it, it is now just like my Bushnell was, except I can't focus the reticle now that I need to. LOL!

Plus, the Excursion was quite a bit heavier, and extremely FRONT heavy, at that. It was annoying how it always wanted to drop forward. The Mk4 is light weight magnesium, and well balanced.
Yeah that's the name of it, (y), I wonder how people who wear Glasses all the time would get on without the Ret Adjustment, I bought the Excursion from someone here of the Hide.