focal planes

Discussion in 'Long Range Scopes and Other Optics' started by Richwv, Aug 9, 2011.

  1. Richwv

    Richwv Member

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    I am looking o buy a new variable scope and had a question about focal planes. It will mainly be used for hunting right now but someday may hopefully serve double duty asa medium to long range competition scope. I thought I understand the difference but am not sure. A lot of things I read say the point of impact changes at different magnificfations in a rear focal plane, i understand how the holdover dots on a mil dot reticle would change but I don't understand how the center of the crosshairs would change their POI? I like the advantages of a 2nd focal plane reticle not being as large at high mag or small at low mag, but do not want to have to take all hunting shots at the same magnification I sighted it in on.
     
  2. ICANHITHIMMAN

    ICANHITHIMMAN Well-Known Member

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    Well personaly I have never owned any quality optic that was not in the first focal plane. I have never had issue with the thicker lines at all. I have 2 Horus Vision, Leupold and a US optics scopes.

    The POI does not shift in a second focal plance scope, the substensions change when you turn down the power. Mils are a set distance, but in a second focal plane optic that is only true at the scope highest power setting. when you back the power down the substension changes. You can work around this if you are sufficnetly trained. Does that help at all?

    Jon
     

  3. kcebcj

    kcebcj Well-Known Member

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    Your point of impact only changes when the distance from the muzzle to the target changes. For instance let's say you sight your rifle dead on at 200 yards while having the power set to 10. Now when you crank it down to 4 and your still shooting at 200 yards' it will hit in exactly the same place just harder to see the bull but you have a better field of view. This holds true for both 1st and 2nd plane scopes.

    I would suggest you go to the web site of the scope you are looking to buy and down load the user manuals for both the 1st and 2nd focal plane scopes. They explain pretty well the difference between the two sub tensions. It may get a little technical but it's not brain surgery.

    Here is a link to the Viper PST scope user manuals for their scopes. If your undecided maybe these will help. They are at the left at the bottom.

    Vortex Optics - Viper PST 4-16x50 FFP EBR-1 MOA Reticle
     
  4. MHO

    MHO Well-Known Member

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    You will be much happier with the FFP. Good luck. As the previous thread, check out the vortex site. Also the PST Viper is a great scope. Own one and soon will have two.
     
  5. Richwv

    Richwv Member

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    Thanks everyone, yes that did help. I understood how any elevation or windage marks on the reticle would change because as I change magnification the space between them would also change. I had just read many places the point of impact also changes and that did not make sense to me. Thanks again for all your help and clearing things up for.
     
  6. rjackh

    rjackh Well-Known Member

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    he said it right
     
  7. Mikecr

    Mikecr Well-Known Member

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    As far as function, if you intend to range with a laser range finder and dial your solutions with turrets, go SFP with a simple med-fine crosshair(if you can get it).
    If you intend to range and hold-off with reticles, go FFP, and whatever reticle you think you can do both with and still hit a small killzone.

    Either way, if you're hunting, don't buy into cheap tactical wannabe junk, but focus on field functions(what you actually need).

    Given that armageddon is not upon me yet(I can still buy batteries), I prefer laser ranging, dialing elevation(in 1/4moa), and holding off for wind(in inches). I prefer a med-fine crosshair like NF's CH1, that works perfect in the field for varmints. Not too small/large, and simple.
    My solutions are taken from a printed off click card carried along.
    I use either MK4 or NXS scopes ~25x.
    My hunting guns are atleast 1/2moa cold barrel accurate(for x distance) off a Harris bipod, and I always position myself to within killzone requirements given this accuracy, or I don't take a shot.
    This is not Hollywood. I get one shot per groundhog, and I can engage multiple GHs at ~30-60sec intervals with my system, provided situations support it.

    I could not range groundhogs with a FFP scope. I could not even see a GH behind the reticle of FFP scopes I've looked through, much less hold-off between hashes with the target aspects GHs typically provide. Maybe that would be different if my targets were pakistanis..
     
  8. Richwv

    Richwv Member

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    Thanks, My initial intentions were to get a VX III with drop turrets and a nikon range finder. I see Zeiss has a rebate programon turrets thru end of year so I might do a conquest and save a couple months for the range finder. I have heard alot if good about the conquest line of scopes but do not have any experience with them. I have only had good experiences with lisping and will probably stay with them. Thanks again for all he info.
     
  9. ICANHITHIMMAN

    ICANHITHIMMAN Well-Known Member

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    I'm a leupold whore myself but tell us your budget and we can help.
     
  10. Richwv

    Richwv Member

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    I have $900 now but also want to get new rings. I have savage original equip rings now.
     
  11. westcliffe01

    westcliffe01 Well-Known Member

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    To your original question:
    Thee are 2 different images in your scope. The image of the target, which is focused by the side focus (move the image focal plane forward and backwards, with the idea that it is focused sharply on your retina). The second is the image of the reticle. If the reticle image plane and the target image plane do not coincide, then the point of impact will shift if you move your eye off the exact optical centerline of the scope.

    To avoid this state of affairs, the recommendation is to point the scope at a featureless surface (plain untextured wall or open sky with no clouds). Then position yourself behind the scope, close the eye, and open it briefly to see if the reticle is in sharp focus. Adjust the eyepiece focus in or out to get the reticle to look as sharp as possible when viewed briefly (if you stare at it, you eye will try to correct for out of focus and fool the brain). When you get it as good as possible, then point at a high contract target and adjust the side focus until the target is sharp. Probably want to do the same routine (look briefly through the scope, then close the eye, repeat) since if you stare at the target the brain will try to correct.

    When the target appears to be in focus (without having adjusted the eyepiece, only the side focus), now align the rifle carefully with a spot on the target and fix the rifle position (gun vice or whatever means you have). Now without touching the rifle or changing the point of aim, move your eye away from the center of the scope and see if the position of the cross hairs moves off the point of aim. Move the eye left, right up / down to see that it stays aligned with the point of aim. If it stays aligned, then all is well for that target distance. Now the procedure has to be repeated at other distances. Obviously at long range it make a bigger difference, but the good thing is that as one approaches infinity the degree of focal shift becomes smaller and smaller on the side focus, whereas a relatively large correction is needed for intermediate distances (100-500yds).

    One of the things to check is whether the scale on the side focus matches in any way the actual distance to the target. Len says that it generally does not, even on high $ scopes. That means one needs a kind of "cheat sheet" for the scale on the side focus wheel, because in the field one seldom has a high contrast target, so after rangeing one needs to simply rotate the side focus to match the range as quick as possible.
     
  12. Code4

    Code4 Well-Known Member

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    It has been explained to me that early variable scopes used a 'worm gear' to shift magnification which ment the reticle moved in a corkscrew fashion as power went up or down. I don't know how it is done now.

    I believe even today German Zeiss scopes can only guarantee a max of 1/2" (The best in the industry) change of POI at 100 yards between max and minimum magnifications with their 2nd focal plane scopes.

    This is all 3rd hand.
     
    Last edited: Aug 12, 2011
  13. Mikecr

    Mikecr Well-Known Member

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    I don't believe this.
     
  14. Code4

    Code4 Well-Known Member

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    If you can post a written guarantee from a Manufacturer please do.