Mil-Dot Question - Confused

[tlk]

How is it that mil dot reticles from different power scopes can be used to determine distance with the same formula? With the higher magnification isn't the target larger and therefore taking up more of the mildots? Or is it that the mildots are spaced differently depending upon the power of the scope? Even then, how would you determine distance in a variable power scope?

Thanks.

 

[NomadPilot]

Or is it that the mildots are spaced differently depending upon the power of the scope?

Yes, that. The mildot reticle in a 22x scope is not the same as a 15x scope.

Even then, how would you determine distance in a variable power scope?

With a second focal plane reticle, the subtensions are only correct at one power setting, usually the highest. If you're not on that setting, you have to do a little figuring. i.e. With a 22x scope at 22x, the mil-dots are 1 mil apart. If that same scope is set on 11x, your dots are 2 mils apart.

Learn More About Mil-Dots in Rifle Scopes

 

[theodore]

Yep! VERY few scopes are made in the front focal plane. A Cabelas I have visited is 100% second focal plane scopes. Don't know about other Cabelas. Sale people didn't understand this but they were friendly.

"the mildots are spaced differently depending upon the power of the scope?"- Second focal? YES -need to calculate the difference, a MIL could now be worth 15 MIL! Depends on scope power range difference.

"the mildots are spaced differently depending upon the power of the scope?"- First focal? N0, any power will not be a problem.

 

[sscoyote]

TLK-- You're going to have to go through a bit of an education here when it comes to multi-stadia reticles in 2nd and 1st focal plane scopes. As has been mentioned most optics use a reticle in the 2nd FP. When u change the power in this type of scope the IMAGE gets bigger while the reticle remains the same size. Which means that the measurment (subtension) between stadia points change as power is changed. This can easily be seen with any scope with a plex-style reticle right out the window of your house. Discreetly pick a tgt. at any distance. While keeping the center X on any point on that tgt. change the power and note where the plex post tips line up on that tgt. As u increase the power the post will get higher on the tgt., or more importantly, the subtension between X and PPT gets smaller. This is why u can only rangefind at 1 power, unless u know what the subtension is at some other power. So in 2FP optics the mil-dot is only accurate at 1 power...BUT it can be used at any other power using the mil-dot mil-relation formula by punching in the subtension at any power u choose. To save time study my last posting on this thread to understand how that works--

http://www.longrangehunting.com/forums/f18/mrad-vs-moa-52395/index5.html

If u have a multi-stadia reticle that's located in the 1st focal plane the reticle changes size as the power is changed. Consequently the measurement between stadia points doesn't change with the power (u can rangefind and downrange zero on any power). U will know if u have a 1st FP reticle as it will catch u by surprise the 1st time u look thru it and change the power.