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 ]
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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!!!
Still playing King of the Hill
Beware the high ground
[Reaching for wallet] You wouldn't happen to be a betting man would you?
Impossible means not done YET!
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'.
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.
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]images/icons/shocked.gif[/img]