I've recently picked up a SWFA fixed 0 power scope. It has a focus from 10 to infinity. It also has an adjustment on the eyepiece, that has a + and a -. The problem is this.
When I am focusing on an object at say 300 yards, the adjustment is on the ten mark. It seems that everything I try to focus on, only will focus on or near the 10 mark. Do I need to adjust the +/- adjuster to get it straightened out?
Also, does anybody have the paperwork or user manual that they could copy for me?
Thanks!
Adam
I can't help you with the paperwork or manual - (email SWFA and request those items from them), but as far as the "focusing" problems you're having it sounds like you haven't set the Ocular (Diopter) to the correct setting for your eye. The Ocular/Diopter is set by turning the rubber-coated ring at the very rear of the Ocular Bell (the end of the scope closest to your eye). The Ocular/Diopter used to set the reticle focus ONLY - it IS NOT used to focus the target image. Setting the Ocular/Diopter is the very first thing that should be done once the scope is mounted. Without the Ocular/Diopter being set correctly and fine-tuned specifically for your eye you will
"chase the focus" as you have been. If you set the Ocular (Diopter) carefully and precisely for you eye that should eliminate the focusing problem you're having.
Parallax isn't the same as focus, but it is closely-related. Parallax error occurs when the reticle and the target don't fall upon the same "plane", causing aiming error and a resulting POI error. The Parallax ring on your scope (the ring that adjusts from
"10" to
"Infinity" on your scope) is used to eliminate parallax error by setting the parallax-free setting to fall on the same plane as the reticle. Environmental conditions notwithstanding, with the Ocular/Diopter precisely set for you eye and the Parallax setting correct for the distance that you're shooting at the target should be in perfect focus.
The SWFA 20X42mm is a fixed 20X so there's no magnification to set to maximum, but other than that the correct procedure for setting the Ocular/Diopter is listed below. The procedure is the same for both fixed and variable power scopes regardless of scope manufacturer, type (knob or ring), or location (Objective Bell, Side mount, or Rear-mount).
NOTE: If the scope is a fixed power unit skip steps 1 as it does not apply.
(1) Turn the magnification ring to maximum (highest power).
(2) Turn the Parallax focus to "Infinity" (the symbol for Infinity looks like a figure eight).
NOTE: Most non-side focus scopes use a ring on the objective bell to adjust parallax, and the distances are usually numbered. Side focus Parallax adjustment knobs may or may not have distances marked.
(3) Turn the Ocular Lens (Diopter)/Eyepiece all the way in (on PMIIs' that's counter-clockwise).
(4) Aim the scope at a cloudless section of the sky (you don't want anything except sky in the view, or else your eye will naturally attempt to focus on the object(s) in the view beyond the reticle. Also, the human eye is drawn to movement: Movement distracts the eye, and clouds are often in motion.
(5) Look at something nearby, but not too close, then look through the scope at the reticle. If the reticle is out-of-focus turn it a bit to begin to focusing the reticle, but look away from the scope.
Never look at the reticle for more than a couple of seconds when adjusting the eyepiece (if you look at the reticle for more than a second or two your eye will naturally begin to adjust to bring the reticle into focus - and you don't want this to happen.
You want to be able to look through the scope and see a sharply focused reticle immediately with your eye relaxed.
This cannot be achieved by continuously looking through the scope and turning the eyepiece into focus in one continuous motion because your eye will have already begun to adjust.
Note that the threads on Diopter adjustments are normally very fine, so you may have to turn the Diopter more than you might expect before any appreciable difference in reticle focus is discernible. You will most likely have to make several small adjustments before you get the reticle perfectly and finely-focused for your eye, but it is very important that you do so. Sometimes the reticle looks fine, but when extra time is spent fine-tuning the Diopter setting shooters' often discover that fine-tuning the Diopter makes a difference. A lot of shooters'
"chase the focus" because they didn't set their Diopter adjustment correctly when they initially set-up the scope. Some even (incorrectly) use the Ocular/Diopter adjustment to focus the target image because they never learned the correct way to set the Diopter is used to reticle focus.
Remember, look away every few seconds and make small adjustments to dial-in the Ocular/Diopter/Eyepiece focus. Once you have achieved this, you should not adjust the eyepiece at all,
except to maintain sharp reticle focus as your vision changes over time
(it always does). You may want to put a pen mark on the eyepiece indexed to the index dot on the scope tube - if the tube doesn't have an index mark use a pencil. That way, if someone else shoots your rifle and adjusts the Ocular you know where to return the adjustment to.
If you cannot achieve simultaneous reticle and image focus after following the above directions for Ocular/Diopter/Eyepiece Focus, it is
possible that there is a problem with the scope.
NOTE: Setting the diopter at the
extreme end of it's adjustment range in either direction can affect the image focus. Also, since all of the lenses in a scope except for the reticle are curved, when using aggressively canted bases (as suggested by S & B for their PMII line) the eye may be pushed out of center of the lens very slightly blurring the reticle, although good eye alignment and head position pretty much eliminate this. I wear glasses (20/15 corrected) and I don't have this problem and I use 45 MOA bases with my PMII 5-25X[56] scopes. The quality of the lenses and coatings, and the user's vision, i.e. astigmatism, can also affect the reticle focus.
Keith
