1st focal plane???? help

In FFP, the reticle subtension doesn't change in size although it appears to as you change your magnification. If you have an MOA reticle and have hash marks 1 MOA apart. they will be 1 MOA apart at 6x, 12.3x, 24x, 32x. It doesn't matter where your power setting is.

In SFP, the reticle changes according to the power setting you're on. There will be a certain power that the reticle is calibrated to. If you have a 1 MOA hash marks, your scope may be set to calibrate at 24x. At 24x the hash marsk are 1MOA apart. If you are at 12X, they are 2MOA apart, 6X are 4 MOA apart. It requires a little math to understand your holds with SFP.
 
i will try. and i'm no expert so someone correct me if i am wrong.

The 1st focal plane is actually the end of the scope closest to the target (objective end). Think of it as the first plane of glass that the light from the target hits when entering the scope.

2nd focal plane is the plane of glass closest to the eye (ocular) end of the scope.

The main thing about focal planes when it comes to scopes is which plane the reticle is located on. If the reticle is on the 1st focal plane, the reticle will be magnified when turning the power of your scope up. Therefore, if you have a drop compensator in your scope, the yardage values will NOT CHANGE with a first focal plane scope when you adjust the power of the scope.

However, if the reticle is in the second focal plane (the end closest to the eye), which is the most common in scopes, adjusting the power WILL AFFECT the yardage values on a bdc reticle. for example, if you have a hash mark under your main crosshairs that is zeroed for 400 yards on 3x power, changing the scope to 9x power will take you from 400 to say 300 yd zero. thats just an example, so don't think that's always the case.

I'm sure there are guys on here that know a lot more about the physics of the focal planes. but i figured i'd chip in since i was bored.
 
First Focal Plane: The size of the reticle increases as you increase power on an adjustable power scope. The reticle will be bigger on 20x than on 4x

Second Focal Plane: The size of the reticle remains the same whether you are on 4x or 20x.


Second focal plane is typically used for hunting and benchrest/paper punching. First focal plane is used more for tactical shooting or any situation where range estimation calculations and precise holdover are crucial.

If you google first focal plane vs second focal plane you'll have enough reading for days.
This link has pictures that show a first focal plane reticle on different powers:
http://www.longrangehunting.com/forums/f18/first-focal-plane-second-40995/
 
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Arcorey...so if im understanding correctly. 1st or 2nd wont affect me when using a ss 10x42. no change of magnafication so no worries. thanks for the insight.
 
That is correct. This is why many of the old mildot scopes like the Unertl were made as straight 10x for the snipers. No change in subtension size, no additional math, much easier. Mil it and drill it
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. I have a Vortex Viper PST in 6x-24x SFP. It is set for 24x. There are indicators at 12x, 8x, and 6x on the power ring to show that it is 2x the subtension value at 12 magnification, 3x at 8 times magnification and 4x for the 6x magnification. If you are looking at mil for your strait 10x, it will always be 1 mil subtension regardless of distance.
 
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Originally Posted By: ARCOREYIn FFP, the reticle subtension doesn't change in size although it appears to as you change your magnification. If you have an MOA reticle and have hash marks 1 MOA apart. they will be 1 MOA apart at 6x, 12.3x, 24x, 32x. It doesn't matter where your power setting is.

In SFP, the reticle changes according to the power setting you're on. There will be a certain power that the reticle is calibrated to. If you have a 1 MOA hash marks, your scope may be set to calibrate at 24x. At 24x the hash marsk are 1MOA apart. If you are at 12X, they are 2MOA apart, 6X are 4 MOA apart. It requires a little math to understand your holds with SFP.

Very good explanation.
 
If you want to confuse yourself some more, or possibly gain greater understanding, try this: Type "infinity parallax" into the PM Google search box. The first thread shown is from a guy asking about the infinity setting on an AO scope. If you go to that thread one of the first few responses has a link to a snipershide article. It will give you a few more definitions of FFP and SFP, as well as some other interesting aspects of how a scope works.

I'm fairly new here and don't know how to do direct links.
 
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