Please explain the advantages or dis advantages of first focal plane.

[DalesCarpentry]

Hi I am seriously considering buying a new Vortex Viper PST. I would like to know the advantages or dis advantages of a first or second focal plane of a scope. This is the scope I am considering.
http://www.vortexoptics.com/product/vortex-viper-pst-6-24x50-riflescope-with-ebr-1-moa-reticle/reticle
Thanks very much and take care Dale

[sscoyote]

Dale the advantage of the 1st focal plane reticle is that the subtensions don't change as magnification is changed. In other words downrange zeroing  and rangefinding with the reticle can be accomplished at any power and it will still be 1 MOA between stadia lines. The disadvantage to 1FP reticles is that the reticle itself gets smaller as power decreases, and can be an issue to some. 1st FP reticle are also referred to as magnifying reticles.

[diggler1833]

Answer your phone Dale. 

Sorry, didn't leave a message this time.

[sscoyote]

Dale, the best place to learn reticle-rangefinding with 1st and 2nd focal plane scopes is oftentimes right out the window of your house--discreetly of course. I used to have an "optics lab" using stds. out the front window of my house. The road ran straight away from it to beyond 1000 yds., and i just measured all the road signs along it and lasered them back to the house. These were my optical stds., if u will, where i did most of my research for reticle-rangefinding. The biggest conclusion i came up with from this "reserach" is that the 2 most important concepts to understand is the inversely proportional nature of reticle subtension vs. magnification using multi-stadia 2nd focal plane reticles, and the versatility of the "modified" mil-ranging formula. I've actually made money off those concepts.

[mrbigtexan]

tell me more

Dale, the best place to learn reticle-rangefinding with 1st and 2nd focal plane scopes is oftentimes right out the window of your house--discreetly of course. I used to have an "optics lab" using stds. out the front window of my house. The road ran straight away from it to beyond 1000 yds., and i just measured all the road signs along it and lasered them back to the house. These were my optical stds., if u will, where i did most of my research for reticle-rangefinding. The biggest conclusion i came up with from this "reserach" is that the 2 most important concepts to understand is the inversely proportional nature of reticle subtension vs. magnification using multi-stadia 2nd focal plane reticles, and the versatility of the "modified" mil-ranging formula. I've actually made money off those concepts.

[DalesCarpentry]

Answer your phone Dale.  

Sorry, didn't leave a message this time.

I did great conversation tonight. Thanks Dale

[sscoyote]

MBT, if you're asking about the making money off these concepts part, it was from a magazine article, and another one soon. Although understanding the mil-ranging formula's application to a 3 MOA TK Lee reticle did net me a hit in a silhouette match at unknown distances i probably wouldn't have had otherwise.