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Does rear focus adjust for parallax?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/08/2009 at 20:55
donlipa View Drop Down
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This has been bugging me for a few days now.  I always thought that the rear focus ring on a scope was to correct for parallax.  I mentioned this while discussing a scope and someone jumped down my throat and said rear focus is to focus the reticle and a side focus is to correct for parallax.  So is this correct?  And yes I have read this (link below) and am re-reading it again slowly because obviously it has not sunk in.

http://www.opticstalk.com/forum_posts.asp?TID=5026
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/08/2009 at 21:14
Horsemany View Drop Down
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You were told correctly.  Generally just focus the reticle with the ocular looking at sky or other solid color.  Focus the target with the AO or side focus.  Some scopes may slightly adjust the focus of targets with ocular adjustments as a side effect.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/09/2009 at 09:23
Dale Clifford View Drop Down
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mostly, the one exception I know of is the swfa 10x which has a rear parallel focus ring- there may be others. this is a great feature -- I wish other scopes had it.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/09/2009 at 20:09
Dave Wilson View Drop Down
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i think all 3 of the SS scopes , 10, 16, and 20x have rear focus? one other version of the 10x has side focus also. i've wondered if the rear focus is as good optically as the front or side versions?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/09/2009 at 20:13
John Barsness View Drop Down
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Though there is some disagreement among optical engineers about this, the rear focus on a conventional scope can correct for a VERY SLIGHT among of parallax, especially if the scope has a wire reticle. I have seen this many times with various scopes, but suspect most of it it just refocusing for different atmospheric conditions.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/09/2009 at 21:38
Horsemany View Drop Down
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I've often wondered John why so many people rave about fast focus eyepieces when it's not something that normally needs adjusting.  On most of my traditional style ocular's I usually set it once and never touch it again.  Now if some are using it to actually focus the image that would be why some think it's the bees knees.  I actually prefer to not mess with it much so my flip up lens covers sit tighter and never have to be moved.  I'm all about simplicity these days except for the bench guns.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/09/2009 at 22:31
John Barsness View Drop Down
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In a big game scope it usually doesn't matter much, unless you're one of those who shoots at over 500 yards.
 
But when testing any sort of rifle for the ultimate 50- or 100-yard accuracy (which is what gun writers pretty much have to do, whether it's relevant or not) I have found it useful to fiddle a little with the ocular focus on scopes that aren't otherwise adjustable for parallax, just to remove what tiny amount of parallax there might be. This does vary slightly from day to day.
 
But this is being really nit-picky--though I did it once last week with a 3-9x centerfire scope on a .22 rimfire and shot a 50-yard, 5-shot group that measured .28". This is kind of fun!
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