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1st plane vs. 2nd plane reticles

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2008 at 10:33
McKinneyMike View Drop Down
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I am trying to decide which of the two types of reticles would be preferable for a variable power scope.  If I understand correctly, a 1st reticle will not change point of impact as power varies and the reticle size will also not vary as power is adjusted up or down.
  If these two facts are true, why would I consider buying a 2nd plane reticle scope?  I maybe misinformed so I ask you to correct me if my information is not correct. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2008 at 10:39
Dogger View Drop Down
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Have a look at this older thread, may help answer some questions.  A well made SFP variable should not change point of impact when changing mag.
 
Welcome to the OT!
 
 
Copied the following from the Leupold FAQ site:
 

11. What is the difference between a front focal plane (1st focal plane) reticle and a rear focal plane (2nd focal plane) reticle?

Most riflescopes utilize a rear focal plane reticle design, creating a situation where the apparent size of the reticle does not change as the magnification is adjusted. In these scopes, the amount of target area covered by the reticle is inversely proportional to magnification; as the magnification is increased, the amount of target area covered by the reticle is decreased. This can be seen by looking through a variable magnification scope and increasing the magnification setting. As the power is increased, the apparent size of the target is increased, but the reticle appears to remain the same size; the result is that the reticle covers less of the target when the magnification is increased.

Rear Focal Plane Reticles – In general, hunting scopes are designed with rear focal plane reticles; this allows the reticle to appear bolder and heavier when set to low magnification, but appear thinner and more precise when set to high magnification. Most hunters set variable magnification scopes to a mid-level magnification for general carry situations, reducing magnification in low-light or heavy cover situations, and increasing magnification for longer, more precise shooting solutions. Rear focal plane designs allow the reticle to appear bolder in low light, making them easy to see and faster to acquire when the light is fading. This same property is advantageous in situations where heavy cover may be encountered, allowing easy differentiation between the reticle and vegetation. If a longer distance shot is to be taken, the magnification can be increased, creating a situation where the reticle covers less of the target, allowing the user to be more precise. If a front focal design were used, hunters would notice that in low-light or heavy-cover situations, the reticle would become much smaller and more difficult to see on low magnification; right when they need the reticle to be bold and easy to acquire.

Front Focal Plane Reticles – Many tactical groups prefer front focal plane designs because common tactical reticles serve a dual purpose: a point of aim and a means of measurement. Reticles such as a mil dot are based on a specific subtension and require exact feature spacing to be accurate; if this type of reticle is used in a rear focal plane design, the scope must be used on a single, specific magnification (typically high power). Placing this type of reticle in a front focal plane design allows the operator to use the scope on any magnification while retaining the exact spacing of the reticle features.




Edited by Dogger - November/15/2008 at 10:57
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2008 at 11:08
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Your first point is true of any well-made scope: point of impact does not change as power changes.  This is true of SFP or FFP.

Your second point could be interpreted to be accurate or inaccurate.  An FFP reticle changes in size proportional to the change in magnification - meaning (if using a mil dot reticle): an object observed to subtend 3 mils at lowest power will subtend 3 mils at highest power and at every power in between.  To accomplish this, the observed size of the reticle changes as the magnification changes.  With a SFP reticle, the observed size of the reticle never changes, so an object observed to be 3 mils at low power will subtend 10 mils at higher power.  This is why SFP ranging reticles must range at a specific power - not at all powers. (That power is usually 10X or max power.)

For hunting, I do not prefer SFP reticles simply because the reticle is difficult to see at low power (or is excessively large at high power - or both.)  With SFP,  I can always see the reticle and am always ready for the sight picture I get.


Finally, if hunting in low light and you decide to get a FFP, I recommend you get it illuminated.  I've lost a few FFP reticles in low light, and jacking up the magnification (to better see the reticle) simply makes the image darker.

If you need to range with your reticle or the power range is not too great, FFP can work well.  If it is a hunting rig and/or has a large magnification range, I wouldn't use FFP unless you need to to range targets or adjust fire with the reticle.


More info on what you plan to do with the scope would be helpful.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2008 at 15:44
Dale Clifford View Drop Down
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point of impact changes with sfp, and depends on the magnification range of the variable as long as cateris parebius, the poi will elevate as the mag power is decreased, this is main theme behind the zeiss rapid Z, leos, varmits and bc reticles and swaros tds reticles and online computer adjustments.  where this occurs is a function of the ballistic flight path of the bullet.

poi doesn't change with ffp
sfp cost about $600 less than ffp all things being equal
ffp reticles gain their biggest advantage in group shoots, ie. tactical swat teams where every one is reading off the same sheet of music.  there is no accuracy advantage. to ffp
the reticle increases in size depending on the ration of the erector assembly, thus a 3x9 ffp will magnify the reticle 3 times a 3x18 will magnify 6 times. you must decide if you like that or not.
 
sfp reticles don't have to be at either the highest magnification or even one set by the company, all you need to know is the ratio of the bars in the reticle and the change, increasing mag. will decrease values  etc.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/17/2008 at 01:45
8shots View Drop Down
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all you need to know is the ratio of the bars in the reticle and the change, increasing mag. will decrease values  etc.

 
Or you could look at a target 100 meters away with a 1 inch grid. Then slowly turn your scope through its magnification range and note how the reticule bars changes at each power setting. From this a handy cheat sheet can be drawn up.
For example I have observed that on 20 x my second bar is exactly 2 inches below my first or main crosshair at 100m. I know that my bullet drops 4 inches at 200yds. So when the target is 200yds away I set the scope on 20x and use the second crosshair.


Edited by 8shots - November/17/2008 at 01:45
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/17/2008 at 07:25
Dale Clifford View Drop Down
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Originally posted by 8shots 8shots wrote:

all you need to know is the ratio of the bars in the reticle and the change, increasing mag. will decrease values  etc.

 
Or you could look at a target 100 meters away with a 1 inch grid. Then slowly turn your scope through its magnification range and note how the reticule bars changes at each power setting. From this a handy cheat sheet can be drawn up.
For example I have observed that on 20 x my second bar is exactly 2 inches below my first or main crosshair at 100m. I know that my bullet drops 4 inches at 200yds. So when the target is 200yds away I set the scope on 20x and use the second crosshair.
 
this is the same method swarovski uses, by the way. from a ballistic program of the load one is using, take the reading for the drop between 200 and 300 yds, this "factor" will be the same for a large group of loads and calibers, then build a drop chart from this. swaro provides a set of stickers with this hit factor with their scopes, one can also range with the "factor". set the top bar on the top of the target, find the bottom match and divide the factor into the known target height x 100 to get yds. distance.
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