Reticles on frontr rear focal plane, why?

Discussion in 'Long Range Scopes and Other Optics' started by EXPRESS, Mar 31, 2004.

  1. EXPRESS

    EXPRESS Well-Known Member

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    Why is it that most scopes have the reticle on the rear focal plane so that when you turn the X up, you get a bigger reticle, which I find so very annoying in most scopes other that what I'd consider for brush and low mag work?

    When you're shooting long range or target it's so nice to have a reticle that stays the same, it also means your ranging doesn't change with the magnification.

    Where are the advanteges?
     
  2. Randy in Va

    Randy in Va Well-Known Member

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    This is too complex to try to repeat here. Your best option is to look at the complete story at the website for US Opticsat
    http://www.usoptics.com/usOptics101.htm

    and look at the section on front/rear tradeoffs.
     
  3. Dimitrios

    Dimitrios Well-Known Member

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    [ 03-31-2004: Message edited by: Dimitrios ]
     
  4. Mikecr

    Mikecr Well-Known Member

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    You got it backwards. The FRONT focal plane type presents the problem growing reticle.

    It's a euro/sniper thing, most of which are mildots. Simple marketing. But as you've figured out(congratulations),these offer little precision, long range potential unless the mildots are in extremely fine subtension(<.25mils).

    Go with Nightforce or Leupold. Ignore the rest.
     
  5. Dimitrios

    Dimitrios Well-Known Member

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    <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> It's a euro/sniper thing, most of which are mildots. Simple marketing. But as you've figured out(congratulations),these offer little precision, long range potential unless the mildots are in extremely fine subtension(&lt;.25mils). <HR></BLOCKQUOTE>

    The Premier reticle GEN2 is .20mil and so is the Klein reticle on some of the S&B scopes, i think thats prety good.
    Personaly i like these FFP reticles...
     
  6. RuffHewn

    RuffHewn Well-Known Member

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    Express, just to be sure we all are speaking the same language: A forward or 1st focal plane reticle magnifies with the tgt so that both maintain same relative size, ranging aids or holdover marks are accurate at any magnification. With a rear or 2nd focal plane reticle only the tgt magnifies so the reticle is relatively smaller as magnification is increased. Is that also your understanding of the two reticle locations?

    If not a 1st plane reticle, then give me a fixed magnification scope. I have the IOR 2.5-10x with illum MP8 in the 1st focal plane on my .300WSM. With my SMK190 load sighted in at 750 yds I can use mil hold-unders regardless of magnification. At 4x I can take out nuisance stray cats at 50 to 100 yds by holding 5 mils low. If I am looking for feral hogs at long range with the scope on 10x and my quarry appears in the shooting lane at 100 yds then the same -5 mil hold is valid. POI shift a magnification is changed is lessened or nonexistant with a 1st focal plane scope. The poster is absolutely correct that stated that the mil dot reticles in many 1st plane scopes are too thick to allow adequate precision for many situations. However the MP8 thin lines are only .05 mil thick. Judging by the 16x IOR MP8 I believe even a 6-24x 1st plane scope could be usable with that reticle design.

    If I must assign an advantage to the 2nd focal plane reticle it is during low light close range work at low magnification. Another advantage only valid for magnifications that approach or exceed 20x with the previously mentioned overly thick mil dot patterns is that a 1st plane reticle would likely obscure too much of the target. That is also the reason that in many high magnification variable magnification mil dot scopes the mils are 1 milliradian at 10x.

    [ 03-31-2004: Message edited by: RuffHewn ]
     
  7. EXPRESS

    EXPRESS Well-Known Member

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    I think I'm confused here.
    Aside from that yes, I can see i had it round the wrong way, thanks.

    I have a Nightforce with NP-1RR reticle that only maintains my holdover points and rangefinding capabilities at 15x. Change it and it all goes out the window.

    Consequently I use it as if it were a fixed power scope.

    Wasn't this supposed to be a front focal plane scope that maintains relativity to target?
    Does it have to do with the fact that is it an irregular reticle?
     
  8. DMCI

    DMCI Well-Known Member

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    I agree with Randy in VA, this is a complex subject, but let me see if I can distill it down.

    1. Rear(2nd)Focal Plane Variables: (Leupold and other US manufacturers)

    a. Reticle is same size at any magnification. Mil Dot subtension changes with power.

    b. Scope good for hunting without ranging because of same size reticle at any power.

    c. Reticle not best for ranging and/or Mil Dots. Often calibration is required to see at what power "mil dots" are Mildots.

    2. Front(1st) Focal Plane Variables: (S&B, USO, and many European Scopes, not for US market.)

    a. Reticle changes size with power. Not best for hunting because reticle can grow and cover target. Europeans have developed special reticles to address this issue such as post, etc.

    b. Good for MilDot reticle because subtension is the same for any power. A Mil is a Mil regardless of magnification setting.

    c. Disadvantage is that with low power, reticle can become very small, so dots, etc are difficult to see.

    There you have it in a nutshell.

    [ 04-01-2004: Message edited by: DMCI ]
     
  9. Randy in Va

    Randy in Va Well-Known Member

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    Very good DCMI but I think you missed a major disatvantage to rear focal plane scopes. As USO states "Why front or rear focal plane placement? Question: What are focal planes and what is the difference between putting the reticle in the front or rear focal plane? Answer: Only in a variable power scope is the reticle placement a major problem. In the rear focal plane, or behind the power changing lens system (erector tube), was the first solution that occurred to optical engineers, and most American scopes are still being built that way. Unfortunately, this apparently ideal solution has a very serious flaw.

    Any tolerance change in the centration of the lens system and their spherical/longitudinal movement with the power change, will shift the point of impact. A variation of one thousandth of an inch will move the zero point approximately one inch at 100 yards. Since the mechanical parts that hold the power changing lens system slide inside each other, (some allowances are made for temperature changes, manufacturing tolerances and wear), there must be some movement made to accommodate this. Consequently this lateral and vertical movement will often shift zero by as much as several inches as power is changed." This would be a good thing for a prarie dog over 300 yards!!!
     
  10. Mikecr

    Mikecr Well-Known Member

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    With the NP-1RR, Nightforce has given you an option to perform limited range estimation with the power set to 15x. Some NF reticles(like the R2) offer both range estimation, and drop compensation potential at a set power. Or, being second plane, you can crank up the power and really get precise. I'm content to use laser ranging and turret adjustments. Unless in a real tactical situation, warranting passive ranging, You could too. Do you need mildots?
    I have both types in hunting/target reticles.
    -A 1st plane Swarovski with TDS. An excellent dear scope.
    -A 2nd plane leupold w/Premier Reticles fine crosshair. This is perfect for long range varminting.
    -Although possible, I couldn't imagine using either scope in the others application. Anyone doing this is handicapped in my opinion.

    I'm glad that both types are offered. You just have to setup with what you REALLY need. Rather than what seems 'cool'.
     
  11. Guest

    Guest Guest

    There are several more problems; however I will mention only a couple. To begin with, a Scope manufacturer of caliber, such as USO will build / assemble a first focal plane reticle correctly. That is to say that the reticle will be placed properly in the erector tube, producing a correctly calibrated reticle. Schmidt Bender does likewise. However there are other manufactures out there that appear to be incapable of achieving this. In addition, whereas the interior components of the USO's are credible, there are other manufacturers whose are not. Once the interior components fatigue, everything will come unraveled including the calibration of the reticle as well as the click adjustments.

    [ask Marty Bordson of Badger ORdinance. It happened to an associate of his he was shoting with last week]

    The next problem that I have personally encountered with poorly manufactured first focal plane scopes is the fact that when on lower power, the reticle will appear to "fish-bowl". If you have ever had a first focal plane reticle before you may know what I mean.

    When utilizing a second focal plane reticle, I set the calibration myself by marking the exact location of power that precisely measures 3.6” at 100 yards. With Night Force, I have not needed to mark the settings as they have proven to be correct.

    [ 04-09-2004: Message edited by: W ]
     
  12. sakofan

    sakofan Well-Known Member

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    This kind of goes out to the IOR people that are here.

    Why, after finally getting into the US shooting market, is IOR going to rear focal plane reticle placement?? [​IMG]

    I dont understand all I know about that one.
    But, the new line of IOR's, are I believe RFP. Anyone explain that one???...sakofan..
     
  13. Jim Maloney

    Jim Maloney Well-Known Member

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    sakofan,

    It's all about giving people what they want. Most guys expect to see a RFP reticule in a scope, it's what us American are used to. IOR was geting a lot of returns because the reticules weren't what people were expecting. That is what prompted the change to RFP reticules.

    FFP reticules don't work well in higher power variables either. Say the 6-24x50 for example, if it were FFP the reticule would barly be visible at 6x and would look like a telephone pole at 24x.

    FFP reticule can be special ordered in any IOR scope but I would hate to see how much $$$ that would cost. [​IMG]

    Jim
     
  14. sakofan

    sakofan Well-Known Member

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    Thanks, Jim. Got the pic too...sakofan..WOW!! Love the new eye piece!