I was looking at the Vortex line and have a question.

[Va varminter]

What does first focal plane reticle mean?

[Hotshot]

I don't have a great scientific answer for you, but I might be able to explain in practical terms.

Most of the traditional scopes that we use for hunting and target shooting have the reticle in the second focal plane. When we adjust the variable power of the scope, the reticle does not change.
When the reticle is in the first focal plane it changes proportionally when the power is changed.
The value would be best used for a tactical application where the reticle is used for ranging at high or low powers depending on the situation.

The ranging feautes of BDC, Balistic mil-dot, Varmint hunter reticle, etc. are true at only one power setting.

[Va varminter]

So the reticle stays the same size in relation to target no matter how much the target is zoomed in or out? Thick cross-hairs cover up small targets as bad at 16x as they would at 4x? That does not sound like a good thing.

[Critter]

Chief advantage of the 1FP design in my view is that the calibrated reticles (those with angular subtension information in the reticle) do not loose calibration as power is changed. This is a significant benefit to those (mainly professionals) functioning under operational time constraints or mental pressure. Having to change power setting to get a true range estimate can be fatal, unless you leave your settings on that particular power setting which limits the capabilities of the scope.

I note that almost all fixed power scopes are FFP. Most low cost hunting scopes are 2FP as there are manufacturing benefits.

One thing that I would like to see in the future, is a digital power scale in the reticle run off the reticle illumination battery.