For those who might be interested in a simple method of remembering what the hell first plane and second plane reticle location means: just think that Europeans are the older or "first" countries and they prefer that their reticles and objects change equally in size as the power is increased or reduced (as in Swarovski, Zeiss, Schmidts etc). If these scopes have range-estimating reticles they will work on any power setting.
America is the "second" country in age and Americans prefer that their reticle stays constant while the object increases or decreases in size. Mildots or whatever only work on one power setting, usually the highest (unless you cut the power in half of course, then you times by 2).
Not my idea, was told to me by an American representative of a European scope company.
I just read this yesterday on Gerards site about his Exbal program;
The basic concept is that the program will use the "holdover" value associated with each reference bar to calculate the distances at which the bullet will strike a "point blank range" target. The point blank target is defined by a circle whose diameter is specified by the user. There is the Zero range at which the bullet would strike the center of the target. Secondly there is the "MIN" range at which the bullet would strike at the top of the circle. And finally there is a "MAX" range at which the bullet would strike at the bottom of the circle.
The reticle specifications for four different reticles are pre-defined. The user has the option of specifying any other reticle configuration. These specifications consist of holdover values for each bar or dot along the verticle axis and a units of measure - Minutes of Angle (MOA), Inches per hundred yards (IPHY), of Mil Radians (MILS).
Finally there are specifications to define the scope being used. They consist of the maximum power and the reticle location. A reticle located in the first focal plane grows or shrinks along with image size when the power is changed. This is common in the Eurpoean scopes. A reticle located in the second focal plane stays the same size as the power and image size changes. This is common in American scopes.
When the second focal plane location is specified, Exbal calculates the actual holdover values that correspond to the actual (operating) power setting. A power factor is also shown, it is the ratio of the operating power to the maximum power. (Note: The power factor can be used to adjust "come ups" computed for the main cross hair when the scope is not at full power setting.)
There are two optimize functions. The first determines the sight in distance (main cross hair) so that that a specified reference bar or dot will strike the center of the circle at a distance specified by the user.
For scopes with reticles located in the second focal plane there is an additional option to determine the power setting needed so that a specified reference bar or dot will strike the center of the circle at a distance specified by the user.
S1 and myself are saying the ame thing, just using different terminology. When I refer to first focal plane, I further explain it as a magnifying reticle. These reticles grow and shrink with change in magnification. For example, the new Gen II mildot in the first focal plane (magnified) will not be entirely visible on a 10X scope set at 10X. Most likley you'll need to dial the power back down to 7X to see the entire reticle. BUT,, the mil spacing will be a correct 1mil between dots on any power setting, from 3 to 10,, the space between the dots will always be 1 mil.
The second focal plane reticles could be used to mil on half power, but you'd have to colminate it to ensure that you are at exactly .5 mils between dots and mark it on the power ring. I wouldn't trust the ring to be exact.
So,, call it what you like it,,, but with a second focal, non-magnified scope, if your max power setting is 42, and you dial back to 31,, you will likley have a very hard time ranging accuartely The magnified reticle eliminated this. The R2 may have overcome this in some way,, but I'm not expierenced with it and would cead that answer to someone who uses the system,, ahhh 'em
After reading what S1 said I got to thinking, at 42X this should give you 1 moa spacing between the vetical bars. Because reducing my 5.5-22 by half down to 11 increases the spacing to 4 moa between bars.
It stands to reason the 42 set twice as high would give you exactly 1/2 the moa it's calibrated for at 21x, which should be 1 moa spacing. This actually would be a good thing for ranging, just larger numbers. Size of target in inches divided by moa is the formula NF gives. Divide both numbers in half just gives you smaller numbers to do the math with, as S1 suggested. You instead use 1/2 the size of target in inches divided by number of "lines", this a much faster way.
Now if you have a 1 moa spacing you could use the formula of "twice" the size of target divided by number of lines (which are now 1 moa apart not 2 moa).
Dividing by the number of lines makes it easy to break up the in between area into a decimal, it's alot easier than breaking up the 2 moa span into a decimal... way easier. Try it.