I need schooling on parallax

Slowbalt

Slowbalt

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Can someone please explain like I am five how to deal with parallax?

Background: I started developing my marksmanship by shooting in a few Mapleseeds last year, and discovered a few things:

- Contrary to my belief, high magnification is NOT an advantage for most shooting

- Parallax is real. I started with regular scopes (Parallax setting at 100 yards) and after deciding to bite the bullet and get an adjustable objective scope, my groups at 25 yards considerably tightened up.

- I am looking into acquiring a few low power optics and find that there are very few with any with adjustable objective. Is parallax any less of an issue with low power (Let's say 2.5x and under)?

Any good resources? I looked but have a hard time getting clear answers...
 
The magnification needed really depends on what you're shooting. I found that for precision rimfire my 2-8x didn't have enough magnification, and 16x was better. But that was off bipod/bags/barricade/etc. When shooting unsupported I'd dial it way back.

For the same objective diameter, the worst-case parallax error is exactly the same regardless of magnification, it's just harder to see.

That said, the parallax error is linearly related to objective size, and low magnification scopes often have smaller objective lenses, so that *will* reduce the parallax error.

Just as an example, for a scope with a 20mm objective lens with parallax fixed at 75 yd, your absolute worst-case parallax error starts out at around 9mm at 10yd, drops to 0 at 75yd, rises to 3mm at 100yd, and hits 17mm at 200yd. With a 50mm objective lens, all of those errors would be 2.5x larger.
 
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You can always find out at what range your scope is parallax free at, and shoot at that range. Your manual should state this distance. Alternatively, fix your rifle in place and align it with targets at differing distance while peering through the scope and moving your head until the crosshairs stop drifting all over the target.
 
Cbf123 said:
Just as an example, for a scope with a 20mm objective lens with parallax fixed at 75 yd, your absolute worst-case parallax error starts out at around 9mm at 10yd, drops to 0 at 75yd, rises to 3mm at 100yd, and hits 17mm at 200yd. With a 50mm objective lens, all of those errors would be 2.5x larger.
Click to expand...


How to calculate this?
 
I can't help with the math related to the optics, but some experience on targets - your sights and your aiming point need to "match" each other. So, for example, the long range double aperture target guys will tell you that it is important to have the correct amount of white around the round black bull to centre properly in their front aperture - not enough white showing, or too much, and you would start loosing points - your groups would enlarge - that is why they had a selection of aperture sizes for that front sight to match the lighting of the day. I found for standard cross hairs in a scope it is similar - at 100 yards, instead of a black "dot", try aiming at a white square that is surrounded by a black rim - say 1" wide black rim, with a 2"x 2" or 3" x 3" white square inside. Your cross hairs will create the visual of four white squares when you are perfectly centered - if you are off in any direction, it is immediately obvious that the "squares" are now rectangles. That gives a very repeatable sighting point. Black cross hairs on a black "dot" sometimes get "lost" in there, and difficult to be as precise, in my small experience. I learned this with a Weaver K3 scope with a 3 MOA dot reticle - Best target to use were 5" black circles, with 4" white centers. That dot reticle would settle right onto the white, and it was quite repeatable to get that white "rim" exactly even, all around the 3 MOA dot. Not target quality, but the little 243 was a very accurate rifle - with that K3 scope, I shot many 3 and 5 shot groups 5/8" to 7/8" inch, multiple times.
 
You will get parallax on a 1 x scope as well, and a red dot on my handgun will move if you move your head.
I think money fixes some of it, as most problems in life.
 
Try distancing your eye back until the scope starts closing in on the side evenly and always center the cross hair dead center every time and it'll help alot
 
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